Yeasts & Fermentation Flashcards
Who discovered yeasts, when?
Louis Pasteur (Circa 1860)
What are the favourable conditions for yeasts?
12-30degrees c
What are some unfavourable conditions for yeasts in the fermentation process?
- High acid
- Too much alcohol
- Lack of oxygen
- Extreme temperatures
What is pied de cuve?
Already-fermenting wine that can be used to kick-start the fermentation process
In what situations would you need to add yeast?
- When rain fall has been substantial prior to picking
- If you want more control over the alcoholic fermentation
- If you want to ensure that fermentation reaches its full course
- If you want to raise alcohol content
- If you want to make a sparkling wine
In what forms can you buy yeast?
- Diluted slurry
- Cake
- Gelatin sheets
- Dried
- Freeze dried
What are some examples of features of lab-made yeasts?
- Resist higher alcohols
- Alcohol yield
- Ability to bring out certain aromas
- Tendency to produce lower levels of acetic acid and ethyl acetate
At what temperature does yeast completely die?
-20c
At what percentage of sugar in the must does fermentation slow and then halt?
Slows at 30%, halts at 60%
Why do high levels of tannins slow the fermentation process?
They stick to the yeast membrane
At what ABV do natural yeasts tend to die?
15-15.5%
How much CO2 is produced from 1hL of must?
4.5hL
What is the most widely used strain of lab made yeasts?
Saccharomyces
What are 3 features of lees contact?
- Higher acid
- More texture
- Complexity of aromas (brioche, toast, bread, butter)
What is the definition of alcoholic fermentation?
The transformation by yeasts and sugars contained in grape must into ethyl alcohol and carbon dioxide
What is chaptalization?
Adding sugar during the fermentation process to increase potential alcohol
What are the two main forms of chaptalization?
- Sugar
- Rectified concentrated grape must (RCGM)
What are some physical signs of alcoholic fermentation?
- CO2 bubbles
- Temperatures in vats rise
- Colours change, juice becomes darker as pigment is more soluble in in alcohol
- Density of liquid decreases
- Volume of liquid increases as heat and CO2 dilate the liquid
What are some physical signs of alcoholic fermentation?
- CO2 bubbles
- Temperatures in vats rise
- Colours change, juice becomes darker as pigment is more soluble in in alcohol
- Density of liquid decreases
- Volume of liquid increases as heat and CO2 dilate the liquid
What are some chemical signs of alcoholic fermentation?
- Conversion of glucose to ethanol
- Creation of other alcohols (sometime, e.g ethanol, methanol)
- High ethers (aromatic molecules)
- CO2 release
How much does CO2 is produced per gram of sugar?
1/4 litre of CO2
