Winetech Technical Yearbook 2022

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of white grape must and the reduction of esters, respectively. To prevent this, winemakers implement a pre-fermentative clarification step which reduces this risk by eliminating most of these enzymes. The clarification also lowers the risk of the production of off-flavours caused by excessive concentrations of higher alcohols and sulphur-containing compounds. Due to these benefits, clarification has become a standard step during white winemaking. However, winemakers should be wary of the consequences of over-clarifying. Indeed, clarification also eliminates lipids, and excessive clarification may result in a stuck fermentation due to lipid deficiency. WHY DO WINE YEASTS NEED LIPIDS? Lipids are found in membranes such as the plasma membrane. In addition to the cell wall, membranes are vital for maintaining the structure and functioning of the cell. Moreover, lipids can

serve as energy reserves in yeasts to be utilised during times of starvation. Lipids are also indirectly involved in nutrient transport and the yeasts’ tolerance to stressors, such as ethanol and cold temperatures. Therefore, alcoholic fermentation cannot progress in the absence of lipids. THE NITTY-GRITTY OF LIPID PRODUCTION IN WINE YEASTS Yeasts primarily produce ergosterol (the yeast version of the human cholesterol and the plant phytosterols), and fatty acids – of particular importance are unsaturated fatty acids (the yeast version of omega acids). It is important to note that the main wine yeast, Saccharomyces cerevisiae only produces unsaturated fatty acids with one double bond along the fatty acid chain. On the other hand, commercially relevant non- Saccharomyces

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WINETECH TECHNICAL YEARBOOK 2022