The role of lipids in brewing: Dissertation

Lipids are an important group of compounds affecting yeast metabolism and the physico-chemical properties of beer.In the present study the role of lipids in brewing was studied in laboratory and pilot scale.The analysis of total fatty acid content of wort was considered as a good method for controlling the separation processes during wort production and for evaluating the quality of finished wort.High concentrations of lipids in wort accelerated fermentation, but increased the loss of bitter substances and decreased the foam stability and the filtrability of beer.If the amount of lipids in wort was too small, the fermentation slowed down and off-flavours occurred.Amounts of fatty acids recommended on the basis of this work are 50 - 100 mg/l in the copper wort and 10 - 20 mg/l in the finished wort.The separation of trub was studied at different temperatures and the removal of trub was most effective at 60 °C.Yeast was enriched with lipids by supplying fatty acids in the wort or by propagating the yeast aerobically.Unsaturated fatty acids incorporated into the cells and into the complex lipids of yeast. They resulted in a reduction of the amount of medium chain length fatty acids in yeast and in beer, increased the synthesis of saturated acids by yeast and decreased the level of esters produced in beer fermentation.Unsaturated fatty acids also decreased the amount of squalene and increased the amount of sterols in yeast.In aerobically grown yeast cells the amounts of sterols and palmitoleic and oleic acids were highly increased compared with anaerobic cells.The greatest difference in the percentage of unsaturated acids between aerobic and anaerobic cells occurred in sterol esters.Traditional, anaerobic pitching yeast was replaced with aerobically propagated yeast, which was rich in sterols and unsaturated fatty acids.A significant reduction in fermentation time and in ester production was achieved.The advantages of aerobically propagated yeast are most noticeable when worts of high specific gravity are fermented.No aeration of wort is required and the risk of oxidation of flavour compounds is eliminated.