When the heat is on, yeast fermentation runs out of puff

摘要

1. The 2008 vintage in southern Australia experienced an increase in cases of stuck fermentation.rn2. The March heatwave was a key factor. Yeast does not thrive in extreme heat or cold, or indeed when subjected to rapid changes in temperature.rn3. Heat stress, transport delays and refrigeration problems gave unwanted microbes a head start, further compromising yeast activity.rn4. High sugar levels led to high amounts of ethanol, which can be toxic to yeast, leading to higher residual suga levels in wine. Higher nutrients can stimulate Brettanomyces/Dekkera yeast during maturation.rn5. Low YAN levels after persistent drought also had an impact.rn6. Simple strategies such as keeping bins and equipment clean, monitoring pH and using the right yeast and nutrients, can give winemakers the upper hand.