Aroma components and their formation in beer
H. Suomalainen and P. Ronkainen
The literature concerning the most important aroma components of beer and their formation is reviewed, and it is evident that little is known about the contributions of the yeast to the aroma of alcoholic beverages. Our own investigations show that the exceptional taste nuance of Finnish lager beer is due to an unusually high content of fusel alcohols and isoamyl acetate, produced by a particular strain of brewer's bottom yeast. Gas chromatography reveals that the same aroma compounds are present in distillates of whisky, brandy, and nitrogen-free sugar fermentations. The central role of yeast in the formation of aroma components has been confirmed by the results of a comparison of the aroma composition of a berry wine of the sherry type with that of original Spanish sherries. Only minor differences are discernible in the composition of alcohols, esters, and acids in the beverages produced from different raw materials. However, when yeast is cultured aerobically in a medium, in which half of the ammonia nitrogen has been replaced either by L( +) valine-, L( +) leucine-, or L( +) isoleuoine-, it is found that the raw material also influences the composition of the fermented product, although to a lesser extent. Isobutyric acid predominates when valine is added; iso-valveric acid predominates when leucine is added, and alpha-methylbutyric acid predominates when isoleucine is added.