Ch 7 -Fermentation And Alcohol Flashcards
What are the two types of fermentation in winemaking?
Alcoholic (AF) and Malolactic (MLF)
What is alcoholic fermentation? What does it produce in addition to alcohol?
This is the conversion of sugar into alcohol by the action of the yeast. It also produces flavours and heat.
Between what temperatures will yeast action and fermentation take place?
Between 5 and 35 deg celsius.
Why is S. Cerevisae suitable for wine fermentation?
Tolerates high levelof alcohol and SO2
When will AF stop normally? For other reasons?
It will normally end when all sugar has been consumed by the yeast.
Other reasons are :
Yeast runs out of other nutrients it needs;
Temp exceeds 35 deg;
Temp falls below 5 deg;
Sugar content may be too high - if extreme may have difficulty or not start at all.
When might a winemaker wish to stop AF before all sugar is converted?
To create a sweeter wine.
How might AF be stopped by winemaker?
Kill or remove yeast.
How can yeast be killed?
Add SO2;
Add grape spirit;
Reduce temperature below 5 deg.
How can yeast be removed from wine?
Filtration from wine temporarily chilled below 5 deg.
What are two important ways a wine maker can control AF?
Choice of yeast;
Temperature management.
What choices can be made on yeast and what influences this?
Ambient yeast or cultured yeast.
Ambient yeast can produce complex flavours but can be be difficult to control and can vary between batches.
Cultured yeast performs consistently and produces attractive flavours.
What happens if fermenting wine gets too hot?
Yeast are killed.
How does fermenting at lower temperature influence the wine style?
Fermentation at lower temperatures avoids loss of volatile (floral) aromas and encourages fruity flavours in white wines.
Why are higher temperatures required for red wines?
Heat is necessary to release tannins and colour from the black grape skins.
How has heat management technology contributed to winemaking?
Many vats have heating/refrigeration systems built in making temperature control easy and contributing to the quality and consistency of modern winemaking.
