Volatile Constituents of Malt Vinegar

Abstract

Gas liquid chromatography was used to fractionate the alcohols, esters, carbonyls and acids in commercial malt vinegars. A qualitative and quantitative study was made using a variety of stationary phases. Porapak Q was found to be the column packing material of choice. Acetaldehyde, ethyl acetate, ethyl alcohol,iso-butyl acetate, n-propyl alcohol, n-butyl acetate, iso-butylaleohoi, n-amyl alcohol, acetoin, propionic acid and acetic acid were identified in a variety of malt vinegars. The origin of these volatiles was investigated by their addition to laboratory acetifications, which enabled an assessment to be made of the probable metabolic routes responsible for the formation and breakdown during acetification. The esters were found to be formed during the initial alcoholic fermentation and not during subsequent acetification. In addition three distinct processes of malt vinegar manufacture were examined to ascertain whether these pathways were operative in commercial practice. Both propionic acid and acetoin concentrations were found to be lower by the Fring's and continuous processes.Increased aeration occurs but lower concentrations were found withlaboratory acetifications, otherwise the pattern and character of the volatiles were the same. Samples obtained during the commercial processes were stored to investigate changes during ‘maturing’. No increase was found in the number or concentrations of the volatiles. There appeared to be little change in general volatile characteristics of vinegar during‘the maturation’ process, although a decrease was found in the lower boiling point volatiles. During the growth of mycoderma on wort, n-propyl and n-amylalcohols increased in concentration. Such an increase would suggest a 'secondary fermentation’ by instant strains of bacteria or yeast arising in the production of both alcohols. Finally the efficiency of continuous acetification in towershaped fermentors was investigated in relation to optimum substrate, temperature and aeration. The estimation of p02 was found to be the most suitable parameter for the control of continuous acetification in tower fermentors.