It is quite often that we have plenty of roasted meat left over after Sunday lunch. Most of this is kept in the fridge for sandwiches or cold salad afterwards. It sometimes happens that there is a particular off-note associated with the meat which makes it unpalatable. That note is commonly called “warmed-over flavour” (WOF) and its one of the principal reasons for loss of quality in any cooked, chilled or frozen meat product. The term ‘warmed-over flavor’ was first used by Tims and Watts in 1958 when they noticed these oxidised flavours developing rapidly after short periods of refrigeration.

The subject has been studied for many years by food research institutes because of the economic losses to the meat processing industry.

It’s been an issue for the fast food service outlets in particular because precooked meats offer convenience and reduced labour costs during preparation. It is usually associated with reheated meats that have been chilled or refrigerated for 2 full days (48 hours) or less. The flavour can also develop in pre-cooked frozen meats after a few weeks. The flavour is usually described as cardboard, stale and rancid but there is great variation amongst sensory panellists as to how it’s described.

The causes are associated with the breakdown of lipids in the meat generally through oxidation. This is helped by the subsequent release of iron in the haemoglobin and myoglobin within the meat muscle, which catalyses these degradation reactions further. Whilst the primary products of oxidation have little sensory impact, it is the componentry from the secondary reactions which is most problematic. The components generated are a variety of aldehydes and ketones, lactones and unsaturated hydrocarbons which have very low sensory thresholds (Byrne et al., 2002).

To reduce the impact of warmed-over flavour, meat processors add preservatives such as antioxidants. These are usually tocopherols, BHT (butylated hydroxytoluene), BHA (butylated hydroxyanisole) and propyl gallate (Shahidi et al., 1987). They are very effective at mopping up oxygen which generates the free radicals that contribute to the flavour reactions. Nitrites and some sodium salts of phosphate (pyrophosphate and mexametaphosphate) are also added to prevent iron from catalysing the reactions too.

More information about the phenomenon is to be obtained from the National Pork Board (www.porkboard.org) (Brewer and Decker, 1998)

I’d be interested to know from readers what home practices they use to keep processed meat suitable for consumption after its been stored in the fridge, and how long they keep it at chill temperatures before tasting it again.

References
 

Brewer, M.S., Decker, E. (1998) What is “Warmed-Over Flavor “? National Pork Board (USA). Fact Sheet
Byrne, D.V., Bredie, W.L., Mottram, D.S., Martens, M. (2002) Sensory and chemical investigations on the effect of oven cooking on warmed-over flavour development in chicken meat. Meat Sci., 61 (2) pp. 127-39
Shahidi, F., Rubin, L.J., Wood, D.F. (1987). Control of lipid oxidation in cooked meats by combinations of antioxidants and chelators. Food Chem. 23 pp. 151-155.