If you’ve ever wondered how peanut butter is made then this article describes how and frankly it’s quite straightforward (Woodroof, 1983). It’s quite a common question for degree courses looking to check understanding on the production of this classic nut spread.
A peanut butter is very simple: a dispersion of peanut oil in peanut solids released due to grinding of roasted mature, shelled, washed, and blanched peanuts.
Cultivation Of Peanuts
Naturally you need peanuts! Most peanuts in 2020 were grown in China (41%), then India (14%), USA (7%), followed by Brazil, Argentina, South-Eastern Asia and Turkey. Similar amounts are consumed in these countries according to TOMRA (2020 report).
Probably just under a thousand varieties of peanuts are grown throughout the world!
Roughly about 2 million tonnes are grown in the USA such as in the South-West states of Oklahoma and Texas, and in the South-East states such as Georgia, Louisiana and Alabama (USDA, 2011).
Some Asian countries such as China, Taiwan and Vietnam have started developing their own cultivars for both the whole nut and processing market.
Of the varieties that come to mind for peanut butter, Spanish and Runners are preferred –chosen for their consistency in size and flavour. Most processors use one type or the other, although a third called the Virginia type is now being added to help with quality.
A peanut from a processor point of view comes in two parts; the kernel and hull. The kernel is a rich source of edible oil (43 to 55%) and protein (28%) whilst the remainder is carbohydrate. The kernel usually makes up about 70% by weight of the whole peanut in a shell.
The oil is made up of fatty acids, 80% of which are unsaturated. Most peanut genotypes contain roughly 50% by weight of oil. Peanut oil is composed of roughly 80% unsaturated fatty acids, with oleic (18: 1ω9) comprising an average of 50% and linoleic (18ω6) 30% of the total fatty acid composition (Mercer et al., 1990).
Protein Content
Peanuts contain between 21.5% and 28.6 w/w protein using the N x 5.46 factor. The same level is found in unstabilised peanut butters.
Peanut Polyphenolics
Peanuts are a good source of antioxidant polyphenolics, such as p-coumaric acid, that may be contributing factors to potential health benefits of their consumption. The presence of antioxidants is helping to fuel the peanut ‘story’ and is contributing greatly to the story regarding the significant health benefits of peanuts.
Tocopherols & Carotenoids
As with most nuts, peanuts contain a variety of all the tocopherols – (α-, β-, γ- and δ-) as well as carotenoids (α- and β-carotene, zeaxanthin, lutein, cryptoxanthin and lycopene).
These nuts also contain plenty of p-hydroxybenzoic acid and the amino-acid tryptophan.
For a product to be labeled as peanut butter, it should contain 90% peanuts while the remaining 10% is comprised of seasonings, sweeteners, emulsifiers, and/or stabilizers (US FDA, 2002).
History Of Peanut Butter
Peanut paste was prepared by the ancient Incas and Aztecs simply by grinding peanuts they had roasted on a fire.
Then in the mid-1880s, 1894 to be precise, Marcellus Gilmore Edson of Canada patents a peanut paste prepared by milling his roasted nuts between two heated metal plates. In 1895, Dr. John Harvey Kellogg patents a process for producing peanut butter which is very smooth and suited to patients with eating difficulties.
In 1903, a doctor called Dr. Ambrose Straub in Missouri patents the first peanut butter making machine.
Varieties
Runner, Virginia, Spanish and Valencia are all typical varieties. The Runner accounts for 85% of US production and is also the most suitable for peanut butter manufacture.
Harvesting Peanuts
Peanut plants are allowed to mature before being mowed. The plants are turned upside down using special machines called peanut inverters. These dig, shake and place the peanut plants, with their peanut pods on top, into rows for field curing.
This process relies generally on open-air drying backed up by solar drying. The pods are separated using a thrasher and deposited in hoppers.
Further mechanical drying is needed to reduce moisture content and there may be further drying needed.
Farmers’ Stock Peanuts
At some point buyers will be introduced to the purchasing set up managed by the farmers. Farmers’ stock peanuts are those the grower will sell to a buyer. Thee are also harvested peanuts that have not been shelled, cleaned or crushed.
The unshelled peanuts are inspected and graded at this point to establish quality and then a price.
Peanuts will be sold for further processing as loose kernels or as in-shell kernels. What is unwanted is foreign material including stones, insects, immature pods. There are other conditions attached which all have penalties associated with them. The USDA for example has a very comprehensive protocol on the purchasing of peanuts.
Grading is conducted at specific points such as buying stations and shelling plants. Most often a few miles from the growing spot.
A pneumatic sampler withdraws a representative quantity of peanuts from the drying wagon. This sample is analysed by the USDA inspector who determines the meat content, size of pods (for Virginia &Valencia), damaged kernels, foreign material, and kernel moisture content. Once the grade is established, the loan or commercial value is determined from USDA price support schedules.
Peanuts are graded very carefully and there are penalties in place if the amount of foreign material is over 4 per cent. As the ratio increases, the penalties also rise.
In this standard, grades are defined by the number of groundnuts counted in one ounce (e.g. 38/42). The size is added to the name of the groundnut type or variety. It’s usual to see the grading as 38/42, 40/50, 50/60, 60/70, 70/80 and so on.
In Europe, the main concerns are the presence of mycotoxins. The level of aflatoxin B1 for example in groundnuts intended for direct human consumption must not exceed 2 μg/kg and the total aflatoxin content (B1, B2, G1 and G2) must not exceed 4 μg/kg. However, a higher aflatoxin content for groundnuts is allowed if the products are not intended for direct human consumption. In such cases, the groundnuts must be sorted or treated before they are placed on the market.
Other elements to be considered are the presence of pesticides and whether any proscribed types have been used. There is also a need for making sure peanuts are free of foodborne diseases like salmonella and E. coli.
Europe currently has no system of grading peanuts and relies on the USA classification system.
Food safety certification is a must but not obligatory. European importers rely on some form of food safety certification. Certification needs to be recognised by the Global Food Safety Initiative (GFSI) and will include the following programmes:
- International Featured Standards (IFS)
- British Retail Consortium Global Standards (BRCGS)
- Food SafetySystem Certification (FSSC 22000).
The page ‘Entering the European market for groundnuts‘ is one of the best guides on this subject.
Pricing Of Peanuts
Salt roasted peanuts are 6 to 10 Euros per kg. but the commonly imported kernels are far cheaper. In 2019 the prices quoted were:-
- Argentina Runners split – 1.2 to 1.3 Euros per kg
- USA Runner – 1.2-1.3 Euros per kg.
- China Hsuji – 1.3 to 1.5 Euros per kg.
The ratio of farmers’ stock to shelled peanuts has been of the order of 25 per cent in many cases because of the losses incurred through poor quality supply and storage, The main issues have been insect damage which may account for up to 8 per cent of losses although a 3 per cent loss is most likely.
Purdue University (West Lafayette, IN. USA) developed the Purdue Improved Crop Storage bags which are plastic bags that reduce oxygen supply and stop insect damage.
The other issue is poor harvests especially due to cold snaps.
In 2017, the USDA reported a total of 1.28 billion lbs. of actual farmer stock, of which 514 million pounds were shelled peanuts. That ratio is 40% and has risen to 52% in 2020. The equivalent farmer stock in 2020 was 2.12 billion and the ratio to shelled peanuts on that basis was 32%. Roasting stock is always a fraction of the shelled peanut stock.
In 2020, there was a roasting stock of 37.3 million pounds versus 717 million pounds of farmer stock equivalent of shelled peanuts. That is only 5 per cent.
Peanut Drying
After harvest, the moisture content of a peanut can be very high, ranging from 30％ to 55％ on wet basis. Peanuts must be dried in time to allow safe storage and usage if they are not to be shelled. The moisture content is reduced to 12 per cent or below. It is not easy to achieve in the field so the pods are often dried at the farm. A typical dryer usually consists of either storage trailers with air channels along the floor or storage bins with air vents.
Fans blow heated air (approximately 35°C [95°F]) through the air channels and up through the peanuts.
Further cleaning may occur depending on their eventual use.
If the peanuts have to be dried before processing then a variety of methods are employed such as solar drying, hot air drying, microwave and radio-frequency drying.
Hot air drying processes are performed in traditional bin dryers or semitrailers with heated air passing through the bed of peanuts (Lewis et al., 2018).
Peanuts are dried to final moisture levels of between 7 to 10 percent.
The moisture content for raw peanut kernels prior to roasting should ideally be about 8.0% w/w to 8.5%w/w. Most drying processes get the moisture content down to 2%w/w (Bagheri et al., 2019).
Preparing The Peanuts By Shelling
Most manufacturing sites are placed close to the sites of cultivation. Once the peanuts are harvested, they must be shelled within a month of picking otherwise they can become mouldy and develop mycotoxins.
The shells used to be discarded but are now being processed further as structural materials. The nuts are cleaned and then packed into 2,000 lb. sacks for transport to the processor. The peanut sacks are loaded into bucket conveyors which take them through the whole process.
All impurities such as sticks, stems, leaves and insects are removed by sieving and gravity separators which rely on discrimination through size and weight. Peanuts are particular dense which makes them ideally suited to this type of separation from extraneous matter. The operation relies on screens, blowers and magnets to remove a great variety of detritus.
Most operations are one- or two-person with easily transportable units that can handle up to 3,300kg/hr. In the USA, their are some operators handling up to 5 tons/hr. In a year, a large-scale processor will handle thousands of tonnes.
The shelling operation has not changed significantly from the early 20th century with much of the development occurring in the 1930s to 50s.
The peanuts in their shell are rolled against iron grates either parallel or perpendicular to flow. Some operators use rubber tyres and wood. the iron grate system is the most effective.
The peanuts are screened at the same time as the shells are discarded or aspirated. Air separators may also be used for shell aspiration.
All peanut kernels are then are graded for size, colour and any defects. They are usually packed into 2,000 pound bags for transport to the processor.
Peanut Roasting
To develop the classic ‘peanutty’ flavour, the peanuts are roasted.
Roasting is also a key step in enhancing the texture, colour and overall palatability of those products made from peanuts.
The peanuts are either roasted dry or in oil. It’s also either a batch or continuous process.
The other critical factor is moisture content which affects the development of flavour especially during roasting.
The batch roaster has the advantage over continuous roasting of being adjusted for varying moisture contents.
The colour of the roasted nut depends on a combination of roasting time and temperature. Most processors would argue that time is the most important aspect of this process. The moisture content becomes proportionately lower as the darkness increases. Willich (1952) comments that the efficiency of blanching is unrelated to the degree of roasting.
The roasting colour of peanuts is usually measured by light reflectance in a colorimeter, giving an L-value in a range from 80 (very light or no roast) to 30 (very dark roasted). The Hunter L-value of roasted peanuts used in high quality dry roasted peanuts and peanut butter falls in the range of 50-51 (Sanders et al., 1989).
The dry (air) roasting method is usually through a continuous heater but batch processing is still very effective as mentioned earlier.
Whatever the case, all the nuts must be roasted evenly on all sides and for the same length of time so that the colour as well as flavour is allowed to develop.
Most conventional batch roasters are heated using natural gas flames as with the Bauer roaster (Bauer and Bros. Co.). The equipment is commonly described as a natural gas-fired revolving or drum oven. The rotation of the oven continuously stirs the peanuts to produce an even roast. Oven temperatures are approximately 430°C (800°F), and peanut temperature is raised to approximately 160°C (320°F) for 40 to 60 min.
In others, the burning fuel is prevented from coming into direct contact with peanuts. Some other processors use electricity for fueling the roasting.
In some other cases, roasting is often a double cook process involving a hot air oven – the first at 132 to 143 °C in the first zone and then 171 to 196 °C in the second. In some businesses they are dry roasted at 160 °C for 20–30 min to prepare roasted, salted peanuts. The oil roasting method is shorter at 147°C for 2 minutes (Damame et al., 1990).
A gas-heated roaster such as the model L5 supplied from Probat Inc., Memphis, Tenn. USA. preheated to 175 C is a good pilot-scale unit for roasting batches of 20 to 25 kg of peanuts. Continuous roasters with coolers are now available handling up to 20 MT/hr in some plants.
A medium roast level is obtained at138 °C for 10 mins. and a color lightness (L), end point of 49.2 .
The most up to date technologies now employ infra-red (IR) roasting. In IR roasting, the material is exposed to IR radiation which interacts, penetrates, and transfers thermal energy in the form of electromagnetic waves throughout the material. Hence, heating occurs uniformly throughout the food mass in IR roasting (Bhinder et al., 2019).
Continuous dry roasting involves various equipment. These types of roaster bring scale-up and labour benefits. The peanuts are moved by conveyoring through ovens or by gravity feeding.
Generally, peanuts are roasted by dropping them through extremely hot air and onto belt conveyoring so that drying and roasting are consistent.
One type in particular relies on a stream of countercurrent hot air that roasts the peanuts. In this system, the peanuts are agitated to ensure that air passes around the individual kernels to promote an even roast.
Roasting alters mainly the fatty acid content and levels of alpha (α), gamma (γ), and delta (δ) tocopherols. Less degradation is observed when the roasting temperature is as low as 140°C. It appears to be the optimal roasting temperature and the point where the paste created afterwards is most acceptable but with only the minimal changes to oil and tocopherol content (de Freitas Floriano et al., 2020).
Operators adjust the roasting process via the number of peanuts permitted on the belt which effectively alters their depth, the heated air temperature, belt speed and any returns that must be added back into the process.
Photometry is the main process control technique for checking when roasting or indeed any form of peanut cooking is completed.
All the heat treatments significantly decrease amino acids such as methionine, tryptophan and in vitro protein digestibility (IVPD). The amount of soluble protein however rises as does the acid value of any kernel oil prepared.
Issues With Roasting
If the temperature settings are too high or too low, whole batches can be lost during the process. In some cases it is feasible for mould damage in the batch to be so severe that aflatoxin production is only noticed at a later stage. Likewise, salmonella and other food related microbiological agents have been found in nuts that have been poorly stored although heat treatment should destroy such agents.
Likewise, over-roasting by whatever process can radically alter the sensory quality of the product although mixing is feasible to ameliorate losses.
Other issues arising relate to poor cooling (see later).
The overall peanut losses throughout the process are around 7 per cent.
Cooling
The peanuts are removed from the roasting process and cooled as quickly as is feasibly possible.
These hot peanuts are cooled to about 30 – 35°C in a perforated sieve or fluidised bed so that cool air is blown around them before conveyed to the blanching machines to remove their skins. This prevents the peanut butter having dark spots and blemishes because of skins retained in the butter. At this stage there may be another phase where peanuts are passed through a gravity separator to remove additional foreign material.
Blanching
Dry blanching is used to remove skins. It is usually used for peanut butter production. It removes the kernel hearts because this affects the flavour.
In a dry blanch process, the peanuts are heated to 138C for 25-30 minutes to crack and loosen the skins. The heated peanuts are cooled and passed through brushes or ribbed rubber belts to shed the skins. Screens are needed to separate hearts for peanut halves.
A good unit for this is the Model EX, Ashton Food Machinery Co., Newark, N.J., USA. Most often kernels are blanched for a 2nd time after discarding damaged kernels.
Alternative blanching technologies use water, spin (steam) and air impact but are increasingly being phased out for peanut butter production.
Air impact blanching relies on a horizontal drum containing the peanuts. The inner surface is abrasive and helps remove the skins. Inside the drum, air jets blow peanuts counter to rotation and the air impact loosens the skins. Abrasion and air impact helps with skin removal.
Water blanching relies on peanuts passing on conveyors through stationary blades. These split the skins. Hot water sprays loosen the skins. The skins are separated off by passing the peanuts through canvass pads. Unfortunately water blanching raises the moisture content back to between 6 and 12 per cent.
The skins are usually sent away as animal feed having a generally low nutritional value.
The nuts are usually inspected with an electronic colour sorter which removes uncooked or over cooked nuts, and finally by human eye to check process quality.
Once the whole nuts have passed their quality assessment, they are finely ground to a paste in a peanut mill. Crunchy peanut butter relies on some nuts being diverted to chopping machines which use knives or a less specific form of milling. The chopped nuts are returned to the peanut butter paste before packaging in jars.
Most peanut butter spreads contain 90% peanuts but other ingredients are added to help extend shelf-life or improve flavour. In the early years of processing, it was commonplace for the butter to split into oil and meal phases. Through experience of the process and better control of the raw peanuts and their initial processing it was possible to control many of these issues.
The phenomenon of a ‘horny’ texture occurs if peanut kernels are first re-wetted following water blanching or dip coating. Any subsequent drying and roasting at a high heat creates a harder texture. Warping of the peanut will occur if the kernel contains more than 7 or 8% moisture following curing and storage.
Oil Roasting
Oil roasting is either a batch or continuous process. It causes more damage to nutritional quality and storage stability than dry roasting.
Before roasting the peanuts have to be blanched so their skins are removed. This is the reason we have placed this particular topic after dry blanching.
In a continuous oil roaster, the nuts are placed on a conveyor through a tank of heated oil. the oil is heated to between 138 and 143 C. Roasting time vary between 3 and 10 minutes depending on the level of colour development and flavour quality. Oil roaster tanks rely on heating elements at teh sies to prevent charring of the peanuts on the bottom.
The oil is monitored for quality and is often filtered to remove charred pieces. Roasting oils are usually coconut oil but cottonseed and peanut oil are also used.
To avoid further cooking, the peanuts are rapidly cooled using air either on a conveyor or with cooling boxes.
Peanut Blending
If more than one type of peanut is used in creating a spread, then the roasted nuts are proportioned. These are usually fed via a hooper above the grinder. Sophisticated units might conduct the blending using air jets.
Although single varieties are used, a mixture of Spanish and Virginia peanuts produces very good spreads. One business blends 65% Jumbo and Virginia with 35% Spanish. Variations allow for the production of a uniform spread each year.
Virginia peanuts tend to produce a coarse grained spread so Spanish peanuts are added to improve consistency. On its own, the Spanish nut produces a smooth but overly oily spread. One of the best mixes is a Spanish variety with an equal proportion of some other peanut.
Viscosity Of Peanut Butter
The rheology of peanut butter has been studied because it is directly influenced by the level of grinding or milling.
A paste of 100% peanuts with no additives and thus unstabilised behaves as a Newtonian fluid. If salt, sugar and vegetable oil is added, the rheology of teh paste alters and becomes non-Newtonian (Citerne et al., 2001).
The Milling Or Grinding Process
Milling or grinding is designed to generate a paste which is defined as granular rather than being pasty. Some leaders in the industry have attempted to define consistency as whether it sticks to the roof of the mouth and then relate it to viscosity measurements. If it is ground too coarse, the spread has a very unpleasant gritty texture.
Milling and grinding influence stickiness. To reduce this stickiness, the viscosity of the butter is reduced which is primarily a function of particle size distribution of various solid peanut materials. As the size distribution becomes more uniform or monomodal as it is often termed, so the viscosity falls.
Some producers achieve a reduction in viscosity by increasing the amount of shear force applied which disperses the particles uniformly in any oil as well as potentially increasing the oil content because of the oil released. In some cases oil is added as a functional prop to help in this case.
The other objective in grinding though is to avoid crushing the oil cells to release too much oil which then contributes to separation.
In the earliest years of production, peanut butter was prepared using a one-step production process but was then superseded. There are some producers still using the approach. Any stabilisers and other ingredients are added to the batch before processing.
The double-milling technique is preferable and routinely employed. The first milling process reduces the nuts to a medium grind and then the second generates a fine, smooth-textured butter. In some cases high pressure homogenization or repeated (multi-pass) homogenization is used to generate the paste of desired consistency.
Most equipment is based on grinding plates or a colloidal mill. The peanuts are fed to the mill under a constant and gentle pressure so that texture is as uniform as possible.
Different forms of mill exist. The grinders might be heavy revolving screws that form the internal centre of the mill. This rough but homogenous mass is passed at constant pressure to adjustable and ribbed grinding burrs or discs.
Worn or overly smooth plates produces a product which is too pasty and causes the oil cells to rupture and release too much oil.
Grinding of any sort produces frictional heat which can ruin the product so cooling jackets are often fitted. Cooling always has to be employed if very finely filled pastes are created. Temperature control is now an established process measure for controlling paste viscosity at the point of grinding. It is also critical to monitor the grinding process to avoid causing rancidity and oil separation issues when the product is stored. Checking the quality of the mill or grinding plates is absolutely essential!
Grinding capacity for large-scale manufacturers is of the order of 800 to 1000 lbs per hour per machine.
Preparation Of Crunchy Peanut Pastes
Crunchy peanut pastes are produced by a mix of coarse ground and broken peanut kernels with smooth butter. Many methods exist but the most common work on removing some of the ribs from the grinder so that a small amount of unmilled peanut falls through.
Another approach means roasted peanuts are broken up to 1/8th the size of a whole kernel. A defined amount is then added to the mixture before filling.
Addition Of Stabilisers Etc.
During the milling process, salt and vegetable oil might be added for stabilisation. The proportion of salt added is between 1.5 and 3% by weight. It can be added before grinding in the hopper or at the point of milling using a feed screw. Salt dispersion must be uniform.
A good unit for milling studies is the Morehouse mill (Morehouse Industries, Los Angeles, Calif., U.S.A.) which has a stone clearance of 0.25mm (10 notches) and is maintained at a constant temperature of 77 ºC.
To comply with HACCP, the paste is pumped through a metal detector to identify any metal shards and through a deaerator to remove air/oxygen which can oxidise the oil and reduce shelf-life. The whole process needs to occur rapidly as the paste retains heat and is liable for overcooking.
Filling Operation
In the past, peanut butter was filled into relatively tall thin jars because the butter was warm and needed to cool rapidly.
The current practice is: deaerated peanut butter is passed into rotating refrigerated cylinders or votators in a batch process or continuously through a heat exchanger. The paste is cooled to 60°–40°C by passing the jars through a chill tunnel.
Having cooled the paste it is now viscous but automatically pumped into depositors.
The paste is then capped using an induction sealer which seals an inner layer over the jar mouth to prevent air ingress. Jars are packed, often by hand to provide a final quality inspection service of both label, cap and jar integrity i.e. glass jar is not fractured or plastic jar is not fractured.
Recent packaging innovations now include filling into pouch packs provided by suppliers in the Middle East and Eastern Europe although these are speciality producers.
Samples of each batch must be taken for microbiological testing before the product is released to market. The product is treated as a semi-perishable food and is not that susceptible to spoilage because it has a low moisture content. The shelf-life depends on peanut quality, curing method and storage of the raw kernels.
The Basic Components Of Peanut Butter For Process And Shelf-Life Studies.
The fat, protein, fiber, moisture, and ash content of peanut butter were determined by AOAC Official Method 871.01 (AOAC), 2001.11 (AOAC), 993.21 (AOAC), 2001.12 (AOAC), and 950.49 (AOAC), respectively.
Oil loss is monitored by centrifugation. Any surface oil is removed and weighted as is the residual peanut butter. The oil loss is calculated as the ratio of the weight of the surface oil to the initial weight of peanut butter.
The adhesiveness of peanut butter is usually measured with a texture analyzer. Peanut butter is compressed and the degree of stickiness computed using the compression force measured.
Confocal laser scanning microscopy (CLSM) is an effective means of checking microstructure. Nile Red solution (5g/L) is the best staining material to pick out cells.
Assessing Spreadability
As well as measuring viscosity, the solids content index (SCI) is a useful measure. It is a good method for correlating spreadability and stability of the butter with the amount and and kind of oil stabilizer used.
Here extracted fat is taken from heated peanut butter. A dilatometric method is employed (Fulton, JAOCS 31, 98, 1954). The less solids the fat contains, the higher the spreadability. There is a careful balance however because enough oil must be present to reduce the chance of oil separation.
Types of Peanut Butter
Three types of peanut butter are available:
- The smooth product with even texture and removal of any particulates.
- Regular butter where the peanut fragments do not exceed 1/16 -in. (1.5 mm)
- The chunky type
Crunchy peanut butter is simple to prepare. Peanut kernels are milled to a coarse granular texture but not crushed. Depending on how crunchy the butter is, a portion of peanuts are finely milled. Salt and oleic acid oil is added through the process until a smooth paste is formed.
The coarse peanut mix is added to create a texture based on sensory appeal.
In recent years there has been a move away from using palm oil as a base for increasing the sensory appeal of peanut butter. This is because of extreme environmental concerns.
Process Manufacturers
- Hinds-Bock Corp., Bothell, Washington (filling equipment)
- Buhler Aeroglide, Cary, N.C., (mills, roasters and dryers). The Lico™ mill is used for grinding nuts to a paste. The grinding chamber’s fast rotating pins and corrugated stator allow operation of the mill at lower temperatures and with minimal energy input according to their web-site.
- Langguth America, Waterloo, Ontario. Canada
- MorehouseCowles…supplier of stone mills
- Satake USA, Stafford, Texas
- Romeinse, Leuven, Belgium
- Tomra Sorting Solutions, West Sacramento, California
- AC Horn Manufacturing, Dallas Texas.
- Wolverine
- LMC (Georgia, USA).
Sensory Profiles Of Peanuts And Peanut Pastes
Peanuts are invariably described as having the following flavour descriptors:
- beany/raw….typical of raw peanut kernels
- bitter……….typical of quinine or caffeine
- cardboard…..associated with rancidity
- roasted……..nutty
- earthy………due to crushed peanut hulls
Peanut flavour depends on genetics and this also transfers to the roasting process (Pattee & Giesbrecht, 1990; Pattee et al., 1993,1994, 1995, 2000a).
Carbohydrates are one of the biggest contributors to flavour in the roasting process. Individual carbohydrate components change during growth and maturation. These compounds also alter with storage and seed size as well as being influenced by genotype (Pattee et al., 2000b).
The main carbohydrates of interest are: inositol, glucose, fructose, sucrose, raffinose, stachyose.
The oxidised flavours created during peanut storage before processing are key flavour and aroma compounds and influence roasted notes in particular.
Walradt et al. (1971) identified a host of compounds typical of roasted nuts but also found in peanuts. These were heterocyclic compounds, sulfur compounds, phenols, ketones, esters, alcohols and hydrocarbons among the roasted peanut volatiles. They also focused on pyrazines: propylpyrazines, ethylpyrazines, vinylpyrazines, methoxypyrazines, and cyclopentylpyrazines in roasted peanut flavour.
Around the same time, Koehler et al., (1971) looked at the odour threshold values of various pyrazines in a number of food samples including roasted peanuts and butter.
Crippen et al. (1992) evaluated roasted peanut flavor quality by correlating volatiles with gas chromatography and a descriptive sensory panel. They showed pyrazines, methylbutanal, methylpropanal and sulphur compounds including methanethiol, carbon disulfide and dimethylsulfide which which were related to dark roasted flavors.
Later studies showed the types of compounds found in roasted peanuts included acetic acid (bread, dough, yeasty), methylpyrazine (grilled chicken, savoury), 3,5,dimethylpyrazine (malty, chocolate), ethyl pyrazines, methyl-ethyl-pyrazines which are often characterised as nutty and roasted, benzeneacetaldehyde (floral, caramel), benzothiazole (rubbery, burnt), and 3-methylpyridine (peanut butter, roasted) (Braddock et al.,1995).
In 1997, Joo & Ho examined the pyrazines in a variety of peanut butters of indifferent to high quality. The most abundant pyrazines were 2,5 (or 2,6)-dimethylpyrazine, 2-ethyl-6-methylpyrazine, and pyrazine which comprised 55-79% of the total pyrazine concentration. There were small quantities of thiazoles, oxazoles, pyrroles, and pyridine.
Reed et al., (2002) identified hexanal, octanal, nonanal, 1- methylpyrrole and pyridine as well as a host of novel pyrazines.
In 2010, Chetschik et al., examined the flavour of raw peanuts versus pan-roasted peanut meal. The flavour profile were compared with commercial peanut products. The compounds, 3-Isopropyl-2-methoxypyrazine, acetic acid, and 3-(methylthio)propanal showed the highest odour activity values in raw peanuts. The compounds methanethiol, 2,3-pentanedione, 3-(methylthio)propanal, and 2- and 3-methylbutanal as well as 2-acetyl-1-pyrroline which is associated with popcorn had the highest odour activity values in the meal.
More than 300 volatile compounds had been identified in roasted peanuts (Lykomitros et al., 2016).
It is generally considered that the pyrazines and pyridines are the key roasted peanut notes.
There is some research suggesting that increasing the roasting temperature improves oxidative stability and also shelf-life. It is thought Maillard browning products such as deoxyosones are responsible .
Peanuts have a relatively high oil content. Peanuts are graded on oil content. A ‘normal’ peanut such as a Tegua and T-P will have a normal oil content. High-oleic acid varieties include Granoleico and GO-P.
Peanut butter has similar sensory descriptors but oiliness is often raised as a major sensory descriptor in the paste rather than describing the peanut kernel.
All flavour notes disappear in peanuts on storage. ASLT studies indicate that peanut butter is slightly more stable than whole peanuts. A loss of pyrazines. A decrease in pyrazines during storage of roasted peanuts has been reported in some research (Braddock et al., 1995; Bett & Boylston, 1992) but not all studies (Warner et al., 1996).
Sensory Aspects And Texture
There are a few studies that have looked at peanut butter texture because smoothness and crunchiness are all key sensory attributes. In one study, a factorial design led to the formation of 27 butter types with three levels of grind (fine, medium and coarse), three salt concentrations (0, 0.6 and 1.2%) and three sucrose concentrations (0, 3 and 6%) (Crippen et al., 1989).
As should be expected, as the level of grinding increased so did attributes such as smoothness, spreadability, adhesiveness and preference ratings. However as a negative attribute, the degree of hardness and adhesion to implements increased.
Raising the level of the added sugar reduced adhesion and hardness as well as reducing the texture but this was countered by the addition of salt which helped with swallowing and improved texture.
Storage Issues In Peanut Butter
The final flavour and aroma quality of both peanut and the oil is strongly influenced by oil stability. That also impacts on rancidity of peanut butter.
[1] Rancidity is still a major issue with butter that has gone past its usable shelf-life. This topic is discussed later but. One of the reasons why some butters become more rancid than other is due to inappropriate processing and then poor home storage. Because of the presence of polyunsaturated fatty acids, peanuts are susceptible to lipid oxidation.
[2] Oil separation often occurs in stored spreads with the peanut solids settling under gravity at the bottom. Peanut oil is less dense than the solids which are protein particles and broken nut fragments. The effect becomes more pronounced as the temperature of storage rises.
Referring earlier to taste issues in [1], the free oil often becomes more quickly rancid than if it was dispersed effectively through the butter.
Gravitational settling of peanut solids over time results in hardening in unstabilized peanut butter (Weiss 1983). One of the main descriptors of poor spread is separation as well as reducing its shelf-life!
The oil which is unsaturated fat exists as a liquid because of the presence of so many double bonds.
To overcome separation, various stabilizers are added. The use of stabilizers started to develop in the late 1940s and 1950s (Freeman & Singleton, 1952).
Vegetable oil such as glycerine, hydrogenated vegetable oils, mono-, di- or triglyceride fractions of vegetable oils, or combinations of these, (Gills & Resurreccion, 2000; Totlani & Chinnan, 2007) or palm oil (Aryana et al., 2000, 2003) are used. They are chosen because their melting points are higher than the usual ambient storage temperature. Their presence helps prevent separation of the peanut butter into a harder, more compact paste with a top layer of peanut oil, released during processing.
The oil is usually added to the butter at a temperature above its melting point. When the butter is chilled, crystallization of the stabilizer occurs and prevents separation or at least slows it down markedly (Woodroof, 1983).
One of the reasons why separation is reduced by the addition of an oil is that its presence increases the spatial distribution of cell wall fragments and protein bodies (Aryana et al., 2000).
Whilst their are considerable concerns about the use of palm oils, unhydrogenated forms have been examined to reduce the adverse nutritional impact of consumption of palm oil (Hinds et al., 1994).
Palm oil as with other oils is added between 1.5% and 2.5% w/w of the peanuts used in the spread. The high palmitic acid (46.8%) and stearic acid (4 to 5.5%) content of palm oil (Rossell et al., 1985) enabled the formation of crystals, which are smaller than those of conventional processors (Weiss 1983).
Commercial stabilisers include Fix-X™ from Proctor & Gamble Co. which is a rapeseed, cottonseed and soybean hardstock oil and is added to between 1 and 2.5%w/w. Some producers add corn syrup solids such as Star-Dri® 42R, supplied by A.E. Staley to 6% w/w.
The formation of organogels has been of considerable interest where stabilising peanut butter is concerned. Freeze‐dried hydroxypropyl methylcellulose and methylcellulose were good stabilizers (Tanti et al., 2016).
Accelerated oil separation tests show that palm oil and Fix-X will reduce oil separation considerably with the latter being the most successful.
There is less free oil in unstabilized and palm oil stabilized peanut butter samples held at 0°C compared to any warmer temperature.
Rancidity In Roasted Peanuts And Peanut Butter
Peanut butter and pastes too are susceptible to rancidity (Agbo et al., 1992).
Rancidity is the development of off-flavours that makes a food unpalatable with unpleasant overtones (Labuza, 1971).
The main reasons for rancidity are due to the formation of lipid peroxides which attacks both fats and proteins (St. Angelo & Ory, 1975a,b,c, 1977, Angelo et al., 1975). The fatty acids in both hull and butter are the most susceptible. Oxygen based radicals produce peroxides which go on to produce changes in the conjugated diene content too.
The major catalysts of lipid peroxidation are iron and copper ions which may be present in retained soil and metalloproteins. To reduce their impact, researchers have used chelating agents such as ethylenediaminetetraacetic acid (EDTA) and citric acid solutions.
The best way to reduce oxidative rancidity is to reduce the oxygen concentration around the roasting process and when the peanuts are being stored.
The main measures of rancidity are the peroxide value (PV), a spectrophotometric assay of conjugated diene hydroperoxides and the p-anisidine value, and thiobarbituric acid reactive substances (TBARS).
Typical rancidity notes include a distinctive oxidised and cardboard flavour.
In some cases, edible coatings confer on the peanut a low oxygen permeability which prevents them taking part in reactions. Another method is to store the roasted peanuts in packaging that has an oxygen barrier and the headspace has been nitrogen-flushed.
High Oleic Versus Non-Oleic Peanut Butter Spreads
High oleic peanuts (HOP) are a special type of peanut which is grown throughout the world. They are said to be naturally sweeter than other varieties but also contain more mono-unsaturated fats than normal oleic acid peanuts (NOP). Such peanuts contain 80% oleic acid and 3% linoleic acid. The overall level is about 30% higher (Moore and Knauft, 1989; O’Keefe et al., 1993).
Peanuts with higher level monounsaturated fats are better suited to those trying to maintain a healthier blood cholesterol level. They also have better oxidative stability on storage as we shall explain later in discussion on rancidity.
High oleic acid peanuts also store better than normal oleic acid peanuts (Reed et al., 2002). They used solid phase microextraction–gas chromatography. HOP had better oxidative stability compared to NOP, which had peroxide values 7–10 times higher. HOP peanuts taste more peanutty probably because of the presence of particular pyridines. They did not develop such potent off-flavours; there were lower levels of aldehydes.
Reducing the water activity is critical for all stored nut products because the levels of oxidation and any sensory changes picked up are less obvious.
The roasting of HOP is an important element because if the roasting process is too robust then they produce more of the higher burnt peanut aroma and burnt peanut flavor compared to normal oleic peanuts (Talcott et al., 2005).
Food Safety Issues
Post-process contamination of peanut butter is possible given the way it is handled and stored in the home. The environment is suitable for Salmonella based on challenge studies (Burnett et al., 2000).
Peanut Butter Brands
A number of well known brands have started to muscle in on the nut spread market. KP Nuts launched their sugar-free and palm-oil free peanut butter in the UK, in July/August 2020.
Similarly launched in July 2020, we find Snickers and M&Ms launched by Mars. The Snickers variant is crunchy and contains chocolate pieces. M&Ms have capitalized on their chocolate coated nuts with a peanut spread.
Have you ever tried Marmite? Unilever produced a crunchy and a smooth spread of 90% nut butter and 10% yeast extract. It has polarised consumers in terms of taste but that is what we would expect (and hope). Their versions contain no added sugar or palm oil too. A recent article has looked further at peanut butter launches in the last few years.
References
Adebiyi, A. P., Adeyemi, I. A., & Olorunda, A. O. (2002). Effects of processing conditions and packaging material on the quality attributes of dry‐roasted peanuts. Journal of the Science of Food and Agriculture, 82(13), pp. 1465-1471 (Article).
Agbo, O. F., Anderson, J. C., & Singh, B. (1992). Lipid oxidation of edible peanut pastes during storage with variation of environmental and processing factors. Peanut Science, 19(2), pp. 101-105
, , , & (2000). Microstructure of peanut butter stabilized with palm oil. Journal of Food Processing and Preservation, 24(3), pp. 229–241 (Article).
, , , & (2003). Functionality of palm oil as a stabilizer in peanut butter. Journal of Food Science, 68(4), pp. 1301–1307 (Article)
Bagheri, H., Kashaninejad, M., Ziaiifar, A. M., & Aalami, M. (2019). Textural, color and sensory attributes of peanut kernels as affected by infrared roasting method. Information Processing in Agriculture, 6(2), pp. 255-264.
Bett, K.L. and Boylston, T.D. (1992). Effect of Storage on Roasted Peanut Quality. Lipid Oxidation in Food, p. 322341. ACS Symposium Series 500, American Chemical Society, Washington, D.C.
Bhinder, S., Singh, B., Kaur, A., Singh, N., Kaur, M., Kumari, S., & Yadav, M. P. (2019). Effect of infrared roasting on antioxidant activity, phenolic composition and Maillard reaction products of Tartary buckwheat varieties. Food Chemistry, 285, pp. 240-251.
Braddock, J. C., Sims, C. A., & O’keefe, S. F. (1995). Flavor and oxidative stability of roasted high oleic acid peanuts. Journal of Food Science, 60(3), pp. 489-493
Burnett, S. L., Gehm, E. R., Weissinger, W. R., & Beuchat, L. R. (2000). Survival of Salmonella in peanut butter and peanut butter spread. Journal of Applied Microbiology, 89(3), pp. 472-477.
Chetschik, I., Granvogl, M., & Schieberle, P. (2010). Quantitation of key peanut aroma compounds in raw peanuts and pan-roasted peanut meal. Aroma reconstitution and comparison with commercial peanut products. Journal of Agricultural and Food Chemistry, 58(20), pp. 11018-11026.
Chiou, R. Y., Tseng, C. Y., & Ho, S. (1991). Characteristics of peanut kernels roasted under various atmospheric environments. Journal of Agricultural and Food Chemistry, 39(10), pp. 1852-1856 (Article)
Citerne, G. P., Carreau, P. J., & Moan, M. (2001). Rheological properties of peanut butter. Rheologica Acta, 40(1), pp. 86-96.
Crippen, K. L., Hamann, D. D., & Young, C. T. (1989). Effects of Grind Size, Sucrose Concentration and Salt Concentration on Peanut Butter Texture 1. Journal of Texture Studies, 20(1), pp. 29-41 (Article).
Crippen, K.L., Vercellotti, J.R., Lovegren, N.V., and Sanders, T.H. 1992. Defining roasted peanut flavor quality. Part 2. Correlation of GC volatiles and sensory flavor attributes, p. 211-227. In Food Science and Human Nutrition. Elsevier Science Publishers B.V.
Damame, S. V., Chavan, J. K., & Kadam, S. S. (1990). Effects of roasting and storage on proteins and oil in peanut kernels. Plant Foods for Human Nutrition, 40(2), pp. 143-148 (Article)
de Freitas Floriano, R., Gräbin, K., Rossi, R. C., Ferreira, C. D., & Ziegler, V. (2020). Impact of roasting conditions on the quality and acceptance of the peanut paste. Journal of Texture Studies, 51(5), pp. 841-848.
, & (2000). Sensory and physical properties of peanut butter treated with palm oil and hydrogenated vegetable oil to prevent oil separation. Journal of Food Science, 65(1), pp. 173–180
, , & (1994). Unhydrogenated palm oil as a stabilizer for peanut butter. Journal of Food Science, 59(4), pp. 816.
Juhaimi, F.A.; Ghafoor, K.; Babiker, E.E.; Ozcan, M.M.; Aadiamo, O.Q.; Alsawmahi, O.N. (2018) Influence of storage and roasting on the quality properties of kernel and oils of raw and roasted peanuts. J. Oleo Sci. 67, pp. 755-762
Labuza, T. P., & Dugan Jr, L. R. (1971). Kinetics of lipid oxidation in foods. Critical Reviews in Food Science & Nutrition, 2(3), pp. 355-405 (Article).
Martín, M.P.; Asensio, C.M.; Nepote, V.; Grosso, N.R. (2018) Improving quality preservation of raw peanuts stored under different conditions during a long-term storage. Eur. J. Lipid Sci. Tech. 120, 1800150.
Mercer, L.C., Wynne, J.C., and Young, C.T. 1990. Inheritance of fatty acid content in peanut oil. Peanut Science 17 pp.17-21. .
Muego‐Gnanasekharan, K. F., & Resurreccion, A. V. A. (1992). Physicochemical and sensory characteristics of peanut paste stored at different temperatures. Journal of Food Science, 57(6), pp. 1385-1389.
Ho, C.-T., Jin, Q.Z., Lee, M.-H., and Chan S.S. 1983. Positive identification of new alkyloxazoles, alkylthiazoles and piperidine in roasted peanut flavor. J. Agric. Food Chem. 31: pp. 1384-1386.
Johnsen, P.B., Civille G.V., Vercellotti, J.R., Sanders, T.H., and Dus, C.A. (1987). Development of a lexicon for the description of peanut flavor. J. Sensory Studies. 3 pp. 9-17.
Joo, K., & Ho, C. T. (1997). Quantitative analysis of alkylpyrazines in regular-and low-fat commercial peanut butter preparations. Bioscience, Biotechnology, and Biochemistry, 61(1), pp. 171-173 (Article).
Koehler, P. E., Mason, M. E., & Odell, G. V. (1971). Odor threshold levels of pyrazine compounds and assessment of their role in the flavor of roasted foods. Journal of Food Science, 36(5), pp. 816-818.
Kornsteiner, M., Wagner, K. H., & Elmadfa, I. (2006). Tocopherols and total phenolics in 10 different nut types. Food Chemistry, 98(2), pp.381-387.
Lee, M.-H., Ho, C.-T., and Chang, S.S. (1981). Thiazoles, oxazoles, and oxazolines identified in the volatile flavor of roasted peanuts. J. Agric. Food Chem. 29 pp. 684-686.
Lewis, M.A.; Trabelsi, S.; Nelson, S.O. (2018) Estimating energy costs of nonbeneficial dryer operation by using a peanut drying monitoring system. Appl. Eng. Agric. 34, pp. 491-496
Lykomitros, D., Den Boer, L., Hamoen, R., Fogliano, V., & Capuano, E. (2018). A comprehensive look at the effect of processing on peanut (Arachis spp.) texture. Journal of the Science of Food and Agriculture, 98(10), pp. 3962-3972.
Lykomitros, D., Fogliano, V., & Capuano, E. (2016). Flavor of roasted peanuts (Arachis hypogaea)—Part II: Correlation of volatile compounds to sensory characteristics. Food Research International, 89, pp. 870-881.
Moore, KM. and Knauft, D.A. (1989). The Inheritance of High Oleic Acid in Peanut. J. of Heredity. 80(3): pp. 252-253.
Mugendi, J. B., Sims, C. A., Gorbet, D. W., & O’Keefe, S. F. (1998). Flavor stability of high‐oleic peanuts stored at low humidity. Journal of the American Oil Chemists’ Society, 75(1), pp. 21-25.
Newell, J. A., Mason, M. E. and Matlock, R. S. (1967). Precursors of typical and atypical roasted peanut flavor. J. Agr. Food Sci. 15 (5), pp. 767-772 .
O’Keefe, S.F., Wiley, V.A., and Knauft, D.A. 1993. Comparison of oxidative stability of high- and normal-oleic peanut oils. J. Amer. Oil Chem. Soc. 70(5): pp. 441-550. .
Pattee, H. E., Giesbrecht, F. G., & Isleib, T. G. (1995). Roasted peanut flavor intensity variations among US genotypes. Peanut Science, 22(2), pp. 158-162
Pattee, H. E., Isleib, T. G., Giesbrecht, F. G., & McFeeters, R. F. (2000a). Investigations into genotypic variations of peanut carbohydrates. Journal of Agricultural and Food Chemistry, 48(3), pp. 750-756.
Pattee, H. E., Isleib, T. G., Giesbrecht, F. G., & McFeeters, R. F. (2000). Relationships of sweet, bitter, and roasted peanut sensory attributes with carbohydrate components in peanuts. Journal of Agricultural and Food Chemistry 48(3), pp. 757-763 (Article)
Reed, K. A., Sims, C. A., Gorbet, D. W., & O’keefe, S. F. (2002). Storage water activity affects flavor fade in high and normal oleic peanuts. Food Research International, 35(8), pp. 769-774 (Article).
Riveros, C. G., Mestrallet, M. G., Gayol, M. F., Quiroga, P. R., Nepote, V., & Grosso, N. R. (2010). Effect of storage on chemical and sensory profiles of peanut pastes prepared with high‐oleic and normal peanuts. Journal of the Science of Food and Agriculture, 90(15), pp. 2694-2699 (Article).
Rodriguez, M. M., Basha, S. M. and Sanders, T. H. (1989). Maturity and roasting of
peanuts as related to precursors of roasted flavor. J. Agr. Food Chem. 37 (3), pp. 760- 765
Rossell JB, King B, Downes MJ 1985. Composition of oil. J Am Oil Chem Soc. 62 pp. 221-30.
Sanders, T. H., Shubert, A. M. and Pattee, H. E. (1982). Maturity methodology and postharvest physiology. In: Peanut Science and Technology (Vol. American
Peanut Research and Education Society, Inc.). (H. E. Pattee and C. T. Young, Eds.). pp. 625-627. .
Sanders, T. H., Vercellotti, J. R., Crippen, K. L. and Civille, G. V. (1989a). Effect of maturity on roast color and descriptive flavor of peanuts. J. Food Sci. 54, pp. 475-477
St. Angelo, A. J., & Ory, R. L. (1975a). Effects of lipoperoxides on proteins in raw and processed peanuts. Journal of Agricultural and Food Chemistry, 23(2), pp. 141-146.
St. Angelo, A. J., & Ory, R. L. (1975). Effect of minor constituents and additives upon peroxidation of oil in peanut butter. Journal of the American Oil Chemists’ Society, 52(2), pp. 38 (Article)
St. Angelo, A. J. S., Ory, R. L., & Brown, L. E. (1975). Comparison of methods for determining peroxidation in processed whole peanut products. Journal of the American Oil Chemists’ Society, 52(2), pp. 34-35
, & (2007). Effect of stabilizer levels and storage conditions on texture and viscosity of peanut butter. Peanut Science, 34(1), pp. 1–9 (Article)
U.S. Food and Drug Administration-Center of Devices and Radiological Health (2002) Code of Federal Regulations. Title 21-Food and Drugs.—Sec. 164.150 Peanut butter. Washington D.C.
Walrat, J.P., Pittet, A.O., Kinlin, T.E., Muralidhara, R., and Sanderson, A. 1971. Volatile Components of Roasted Peanuts. J. Agric. Food Chem. 19 pp.972-979.
Warner, K.J.H., P.S. Dimick, G.R. Ziegler, R.O. Mumma, and R. Hollender (1996) ‘Flavor-Fade’ and Off-Flavors in Ground Roasted Peanuts as Related to Selected Pyrazines and Aldehydes. J. Food Sci. 61 pp. 469–472
Weiss, T.J. (1983). Food oils and their uses. Westport, Conn.: The AVI Publishing Co., Inc. p 14.
Willian, D.A.; Goneli, A.L.D.; Souza, C.M.A.d.; Gonçalves, A.A.; Vilhasanti, H.C.B. (2014) Physical properties of peanut kernels during drying. Rev. Bras. Eng. Agr. Amb. 18, pp. 279-286.
Woodroof, J.G. (1983) Peanut butter. In: Peanuts: Production, Processing, Products. 3rd ed. Westport, Conn.: VI Publishing Company Inc. pp. 181-227.
I used this for my essay on food processing. I bet people are copying from this site all the time. I know they recommend it at Michigan State for concise writing in the food course. Keep it going. I think you should write more on ingredients. Seems a bit easier to follow than a massive wiki article.