Winetech Technical Yearbook 2022

I

NOVEMBER

ISTOCK

IT IS HARVEST TIME and the grapes have been picked and destemmed. Sugars are looking good, and the Yeast Assimilable Nitrogen (YAN) is on target. The recipe for a perfect vintage. The grape juice is prepared and ready to ferment – what could go wrong? Fast-forward to the post harvest celebration. The sounds of Méthode Cap Classique popping open can be heard over excited chatter as the bubbles flow. The fires are lit, and everyone has the best time rejoicing in a successful harvest. Not so fast … and in stomps a sullen and puzzled winemaker. It is the fermentation tanks, and the bubbles are, in fact, not flowing. The fermentations have become sluggish. With the risk of stuck fermentation, there is nothing to rejoice about as of yet. Perhaps there was something no one had considered. Something like vitamins, and specifically thiamine? WHAT IS THIAMINE? Thiamine (also known as vitamin B1) is one of the most essential micronutrients required by yeasts. They need this water soluble vitamin to grow, reproduce and, more importantly for winemakers, ferment. Unlike us mammals, most yeasts, including Saccharomyces cerevisiae , can synthesise their own vitamin B1. This is great, because thiamine and its biologically active forms are essential cofactors for central carbon (sugar) metabolism pathways. These include the ethanol-producing glycolysis, the pentose phosphate pathway for aromatic amino acids, and the organic acid-yielding tricarboxylic acid pathway. Without thiamine, several enzymes of these pathways simply cannot function. Thiamine can also protect yeasts during stressful fermentation conditions by playing an antioxidant role. This provides a defence against free radicals and can prevent oxidation – both are welcome news for winemakers. IMPACT ON AROMA PRODUCTION Beyond its impact on fermentation, thiamine deficiency can also alter aroma compounds produced by the yeasts. This vitamin is important for amino acid breakdown, such as during the production of some aromatic compounds in the Ehrlich pathway. These include some esters, volatile fatty acids and

The role of thiamine in sluggish fermentations and crushed dreams

HERE IS SOME USEFUL INFORMATION ON PREVENTING THIAMINE DEFICIENCIES FROM SLOWING YOUR FERMENTATIONS.

BY JAMES DUNCAN & BENOIT DIVOL

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WINETECH TECHNICAL YEARBOOK 2022