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JOURNAL OF BIOSCIENCE AND BIOENGINEERING Vol. 106, No. 4, 317–323. 2008 DOI: 10.1263/jbb.106.317

© 2008, The Society for Biotechnology, Japan

REVIEW
Beer Volatile Compounds and Their Application to Low-Malt Beer Fermentation
Michiko Kobayashi,1 Hiroshi Shimizu,2 and Suteaki Shioya1*
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka565-0871, Japan1 and Department of Bioinformatic Engineering, Graduate School of Information Science and Technology, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan2
Received 27 August 2007/Accepted 24 June 2008

Low-malt beers, in which the amount of wort is adjusted to less than two-thirds of that in regular beer, are popular in the Japanese market because the flavor oflow-malt beer is similar to that of regular beer but the price lesser than that of regular beer. There are few published articles about low-malt beer. However, in the production process, there are many similarities between low-malt and regular beer, e.g., the yeast used in low-malt beer fermentation is the same as that used for regular beer. Furthermore, many investigations into regular beer areapplicable to lowmalt beer production. In this review, we focus on production of volatile compounds, and various studies that are applicable to regular and low-malt beer. In particular, information about metabolism of volatile compounds in yeast cells during fermentation, volatile compound measurement and estimation methods, and control of volatile compound production are discussed in this review, whichconcentrates on studies published in the last 5–6 years.
[Key words: beer fermentation, esters, higher alcohols, yeast metabolism]

Low-malt beers, in which the amount of wort is adjusted to less than two-thirds of that in regular beer and the malt carbon source is compensated by adding sugar syrup, are popular in the Japanese market. Moreover, new alcoholic beverages that taste like beer, inwhich a nitrogen source extracted from materials other than wort and sugar syrup is used, are acceptable. The liquor tax on Japanese alcohol beverages depends on the percentage of malt. Therefore, beverages with low concentration of malt are taxed at lower rates than beer made from all malt wort. In low-malt beer, volatile compounds produced by yeast metabolism are important for approximating theflavor of regular beer. During low-malt and regular beer fermentations, as by-products of yeast metabolism, sugars in wort are converted to ethanol and volatile compounds, such as higher alcohols and esters. The volatile compounds are different from aromatic compounds in malt and hops, and many of them cause undesirable flavors when their concentration exceeds certain thresholds. Some volatilecompounds are reduced in concentration during maturation, which follows fermentation. However, a fraction of higher alcohols, esters, and other carbonyl compounds remain, thereby affecting the flavor of the final product. Therefore, it may be necessary to keep the concentrations of volatile compounds in the final
* Corresponding author. e-mail: shioya@life.sojo-u.ac.jp phone/fax: +81-(0)6-6879-7444317

product below their taste thresholds so that they do not produce salty, sweet, bitter, or acid flavors. A major difference between low-malt and regular beer fermentations is that the free amino acid nitrogen (FAN) concentration in low-malt beer wort is low at the beginning of the low-malt beer fermentation process. After nitrogen source depletion, proliferation of yeast cells ceases. Thus,the amount of FAN in the wort affects the number of yeast cells proliferated. To make fewer yeast cells consume the same amount of carbon sources than those in regular beer fermentation, yeast cell activity has to be maintained by increasing the temperature. However, high temperature fermentation can result in higher concentrations of volatile compounds. Therefore, it is important to know the...