Baijiu – the Spirit of China

Many many years ago, when I was a student, I celebrated a Chinese New Year with some of my Chinese lab colleagues. Handed round was a clear, highly alcoholic liquor which appeared like vodka or a clear gin but they called baijiu. I downed a few and thought this probably wont catch on because we have our own versions of heavy spirit. Years and years later, it’s a drink that is still largely unknown in the West but is extraordinarily popular in its country of origin, China. Something like 10 billion litres are sold annually which makes it the most widely consumed spirit of all time. We now know of 14,000 distilleries producing just this liquor.

Historically, baijiu (or shaojiu) has been brewed and distilled for well over two thousand years. By the way, the Chinese have been producing liquor of one form or another for over nine thousand years so its not a surprise that baijiu may well have developed one of these earlier drinks. The national liquor of China has a mystique all its own. It started so it is said during the Western Han dynasty which is from 202 BCE to 8 AD. That piece of information was found inscribed on the tomb of Haihunhou.

Baijiu is prepared conventionally from a number of grains. It could be sorghum alone or mixtures from rice and wheat, corn, millet, peas as well as with sorghum. It relies on a fermentation of these grains using a fermentation starter. Juiqu is what a yeast starter is to beer and lager – each one has its own characteristics. Juiqu is also mixed with grains to convert starch and other carbohydrates to sugar and then ferment it to alcohol. The process is typical of a solid-state fermentation

The liquor is based on highly individualistic fermentations with each producer relying on trade secret to produce their particular unique brand of spirit. The divisions are reminiscent of different qualities of soy sauce or Japanese sake and this reflects not only these myriad fermentations but the post-processing options available to the brewer. The alcohol content varies from anywhere between 40% and 55%.

Baijiu then comes in three traditional forms. There are others produced in other parts of the Far East but authenticity is everything with this spirit (Liu & Sun, 2018). The officionados consider 12 aroma types:-

(a) Strong (or Luzhou-flavor); (b) Soy sauce. Moutai (or Maotai-flavor); (c) Light (or Fen-flavor); (d) Rice; (e) Chi; (f) Drug; (g) Zhima; (h) Nongjiang; (i) Feng; (j) Heavy fragrance; and (k) Laobaigan (Xu et al., 2017).

Strong Aroma Baijiu is said to be closest to the traditional, original or classic liquor. Distilleries predominate in Sichuan province. It relies on a simple grain fermentation which is based on one ingredient or on a mixed grain fermentation which relies on many types. Some of the most expensive have been blended in pits for centuries. It has a sweet and fruity taste.

The Guojing sesame-aroma liquor is becoming the predominant sort (Hong et al., 2020). It was accidently discovered when the People’s Republic of China was founded in the mid-part of the 20th century.  

One of the most famous baijius in the world is Moutai, which is produced in the town of Maotai in China. It commands a high price because of its particular fermentation and distilling process. A lot of fake moutai is produced so looking out for counterfeits is important.

One of the top 10 is Yanghe Daqu baijiu which is one of the strong aroma types. IOt was developed in the Sui and Tang dynasties but became much more popular in the Ming and Qing dynasties. It has been named a nation-level liquor three times. The alcohol level is 52%.

The Fermentation

The method of baijiu-making is based on solid-state fermentation and
distillation. This includes mixing sorghum grains, water, and a fermentation agent called jiuqu, daqu, xiaoqu, or mijiu. It is followed by incubation and solid-state fermentation in an underground pit or buried jar for long periods of time. the flavour development depends on a great many factors:-

• the type and age of the materials for fermentation
• The Qu – a mixture of bacteria, molds and yeast
• the aging process as well as the age itself
• the age of the pit
• the type of fermentation

Rather like gin, a vast range of distillates are created (Jia et al., 2020) through a combination of these processes.

When I heard there were 508 microbial species involved in generating flavour and aroma, it was apparent that anybody trying to understand the complexity of the product would have a job for life.

Qu

Qu is the Chinese term for bacteria, yeast and molds. It is the classic starter culture which has many uses in a great deal of Chinese undistilled beverages too. The mold is Aspergillus which means it serves a similar function to koji that is required for miso, shochu and saki production. This mold breaks down starches in the grins to its component sugars in a process of saccharification. The yeast produces alcohol from the sugars generated whilst the bacteria produce various flavours.

Taking Strong Aroma Baijiu as a basic example of fermentation, the materials for fermentation are predominantly sorghum, rice and glutinous rice, corn and wheat. These are ground to leave just the grains and husks. The husks are important to flavour development. Hot water is added to soak the grains to make them suitable for fermentation. They are soaked for up to 20 hours to make sure the grains swell.  These grains are mixed with the husks.

The starch in the grains starts to breakdown through enzymic action similar to the malting process in beer brewing. To encourage this process the grains are steamed. As with any ‘fermentation’ the moisture level is controlled.

The whole mixture cools with workers spreading the grains out in warehouses so they cool evenly.

The Qu is added at a fermentation temperature and blended into the grains. There is a 24 hour fermentation period at a constant temperature. The blending process means that the grains come into contact with as much as Qu mixture as possible. The whole lot including old mash are blended and poured into stone pits.  The ratio of fresh to old mash is a closely guarded secret.

In this part of the process, he fermentation to alcohol begins properly. The stone pits help to maintain and even temperature throughout.

Following fermentation, the mash is transferred to a a distillation tank. It is then distilled. The spirit cut means that the spirit head and tail is ‘cut’ from the heart. Different qualities and quantities are generated this way. 

Analysis

A vast number of articles have been written about the flavour of baijiu and they probably cover every method ever invented. We have:-

• chromatography with mass spectrometry (Dong et al., 2020; Yan et al., 2020; Zhang et al., 2020).
• spectroscopy
• colourimetric sensor arrays – a powerful technique which also includes rapid extraction and sophisticated data management because of the complex analytes (Chen et al., 2020; Xu et al., 2020; Yalcin et al., 2020).

Aroma and Flavour

Every spirit is unique in flavour and aroma and baijiu is certainly no different. Trying to uncover the flavour of baijiu is really a thankless task because there are so many different types. It is fair to say that no one product represents another. Like whisky, preference is all in the beholders tongue.

Freshly distilled Baijiu is characterised by undesirable flavour characteristics which can be described as peppery, harsh, pungent, green, and unpleasant. Aging is critical for developing the desirable flavours (He et al., 2021)  .

One study found nearly 1900 different volatile compounds which included a plethora of  organic acids including acetic, lactic, malic, tartaric, and linoleic acids. There are esters such as ethyl acetate, ethyl lactate, and ethyl hexanoate, alcohols, aromatics, ketones, heterocycles, nitrogenous compounds,  aldehydes, terpenes, sulfur compounds, acetals, and lactones (Liu & Sun, 2018). There are over 510 esters of various sorts in the drink and this may be as much to do with the 508 different microbial species as any other.

Groups of flavours have been examined in some detail over the years. The esters always make a significant contribution (Xu et al., 2022). A number of volatile sulphur compounds are known which are potently odour active (Fan and Qian, 2005; 2006; Fan et al., 2012).

Aging baijiu produces more acids, various long-chain ethyl esters, terpenes and pyrazines.

Fake products have always been with us but trying to outwit the counterfitters can be challenging at best. A simple colourimetric sensor array method was developed by Ya et al., (2012) as a method.

Nutritional Properties.

We wouldn’t normally make claims for any alcoholic product but interestingly, the fermentation produces some intriguing small peptides. One peptide is a tetrapeptide called  Ala-Lys-Arg-Ala, which is especially known to come from sesame flavor-type baijiu. This and others will induce antioxidant defense
mechanisms (Yang et al., 2010; Wu et al., 2017).

References

Chen, H., Wang, S., Fu, H., Chen, F., Zhang, L., Lan, W., Yang, J., Yang, X., & She, Y. (2020). A colorimetric sensor array for recognition of 32 Chinese traditional cereal vinegars based on “turn-off/on” fluorescence of acid-sensitive quantum dots. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 227, 117683

Dong, W., Guo, R., Lin, W., Liu, M., Shen, C., Sun, X., Sun, B., & Deng, B. (2020).  Polyamine-modified magnetic graphene oxide nanocomposites and HPLC-MS/MS allow the determination of two indolic derivatives in strong-aroma types of base baijiu. Journal of Agricultural and Food Chemistry, 68, pp. 3594–3606

Fan, Q., Wang, X., Zhao, Y., Zheng, F., Li, H., Zhang, F., Zhang, Y., & Chen, F. (2019). Characterization of key aroma compounds in Laobaigan Chinese baijiu by GC × GC-TOF/MS and means of molecular sensory science. Flavour and Fragrance Journal, 34, 514–525

Fan, Y., Zhang, L., Jia, J., Chen, H., Fu, H., & She, Y. (2020). Development of a triple channel colorimetric paper sensor array based on quantum dots: A robust tool for process monitoring and quality control of basic liquors of Baijiu. Sensors and Actuators B: Chemical, 319, 128260.

Fan, W.L., Qian, M.C. (2005). Headspace solid phase microextraction and gas chromatography-olfactometry dilution analysis of young and aged Chinese “Yanghe Daqu” liquors. J Agric Food Chem 53(20) pp. 7931–8

He, Y., Chen, S., Tang, K., Qian, M., Yu, X., & Xu, Y. (2021). Sensory characterization of Baijiu pungency by combined time-intensity (TI) and temporal dominance of sensations (TDS). Food Research International, 147, 110493.

Hong, J., Tian, W., & Zhao, D. (2020). Research progress of trace components in sesame-aroma type of baijiu. Food Research International, 137, 109695.

Jia, W., Ma, R., Hu, L., & Mo, H. (2022). Synergy of physicochemical reactions occurred during aging for harmonizing and improving flavor. Food Chemistry: X , 17 100554.   .

Jia, J., Wu, M., Wang, S., Wang, X., Hu, Y., Chen, H., Yu, Y., Shen, C., Fu, H., & She, Y. (2020). Colorimetric sensor array based on silver deposition of gold nanorods for discrimination of Chinese white spirits. Sensors and Actuators B: Chemical, 320, 128256

Jin, G., Zhu, Y., & Xu, Y. (2017). Mystery behind Chinese liquor fermentation.  Trends in Food Science & Technology, 63, pp. 18–28.

Li, W.; Chen, S.-J.; Wang, J.-H.; Zhang, C.-Y.; Shi, Y.; Guo, X.-W.; Chen, Y.-F.; Xiao, D.-G. (2018) Genetic Engineering to Alter Carbon Flux for Various Higher Alcohol Productions by Saccharomyces Cerevisiae for Chinese Baijiu Fermentation. Appl. Microbiol. Biotechnol. 102, pp. 1783–1795

Li, J., Li, L., Zhang, J., Huo, D., Hou, C., Zhou, J., & Luo, H. (2019). Metal ions regulated Ag NPRs etching colorimetric sensor array for discrimination of Chinese baijiu. Sensors and Actuators B: Chemical, 297, 126715

Li, H., Qin, D., Wu, Z., Sun, B., & Sun, X. (2019). Characterization of key aroma compounds in Chinese Guojing sesame-flavor baijiu by means of molecular sensory science. Food Chemistry, 284, pp. 100–107.

Liu, H., & Sun, B. (2018). Effect of fermentation processing on the flavor of Baijiu. Journal of Agricultural and Food Chemistry, 66(22), pp. 5425–5432 (Article).

Wang, J., Chen, H., Wu, Y., & Zhao, D. (2022). Uncover the flavor code of strong-aroma baijiu: Research progress on the revelation of aroma compounds in strong-aroma baijiu by means of modern separation technology and molecular sensory evaluation. Journal of Food Composition and Analysis, 104499.  .

Wu, J.; Huo, J.; Huang, M.; Zhao, M.; Luo, X.; Sun, B. (2017) Structural Characterization of a Tetrapeptide from Sesame Flavor-Type Baijiu and Its Preventive Effects against AAPH-Induced Oxidative Stress in HepG2 Cells. J. Agric. Food Chem. 65, pp. 10495–10504.

Xu, Y., & Ji, K. (2012). Moutai (maotai): Production and sensory properties. Alcoholic Beverages, 25(S60), pp. 315–330 (Article) 
Xu, Y., Sun, B., Fan, G., Teng, C., Xiong, K., Zhu, Y., & Li, X. (2017). The brewing process and microbial diversity of strong flavour Chinese spirits: A review. Journal of the Institute of Brewing, 123(1), pp. 5–12 (Article). 

Xu, Y., Zhao, J., Liu, X., Zhang, C., Zhao, Z., Li, X., & Sun, B. (2022). Flavor mystery of Chinese traditional fermented baijiu: The great contribution of ester compounds. Food Chemistry, 369, 130920.

Ya, Z.; He, K.; Lu, Z.; Yi, B.; Hou, C.; Shan, S.; Huo, D.; Luo, X. (2012) Colorimetric Artificial Nose for Baijiu Identification. Flavour Fragr. J. 27, pp. 165–170 (Article)

Yan, Y., Chen, S., He, Y., Nie, Y., & Xu, Y. (2020a). Quantitation of pyrazines in baijiu and during production process by a rapid and sensitive direct injection UPLC-MS/MS approach. LWT – Food Science and Technology, 128, 109371.

Yan, Y., Chen, S., Nie, Y., & Xu, Y. (2020b). Characterization of volatile sulfur compounds in soy sauce aroma type baijiu and changes during fermentation by GC x GC-TOFMS, organoleptic impact evaluation, and multivariate data analysis. Food Research International, 131, 109043.

Yang, T.; Li, G.; Wu, L.; Zhuang, M. (2010) Research on Health Factor in Liquor & Breeding of Health Factor-Producing Bacteria and Its Application in Liquor Production (I) Research on Health Factors in Chinese Liquor. Liquor-Mak. Sci. Technol. 12, pp. 65–69