Yeasts & Fermentation

Question 1

Who discovered yeasts, when?

Answer 1

Louis Pasteur (Circa 1860)

Question 2

What are the favourable conditions for yeasts?

Answer 2

12-30degrees c

Question 3

What are some unfavourable conditions for yeasts in the fermentation process?

Answer 3

• High acid
• Too much alcohol
• Lack of oxygen
• Extreme temperatures

Question 4

What is pied de cuve?

Answer 4

Already-fermenting wine that can be used to kick-start the fermentation process

Question 5

In what situations would you need to add yeast?

Answer 5

• 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

Question 6

In what forms can you buy yeast?

Answer 6

• Diluted slurry
• Cake
• Gelatin sheets
• Dried
• Freeze dried

Question 7

What are some examples of features of lab-made yeasts?

Answer 7

• Resist higher alcohols
• Alcohol yield
• Ability to bring out certain aromas
• Tendency to produce lower levels of acetic acid and ethyl acetate

Question 8

At what temperature does yeast completely die?

Answer 8

-20c

Question 9

At what percentage of sugar in the must does fermentation slow and then halt?

Answer 9

Slows at 30%, halts at 60%

Question 10

Why do high levels of tannins slow the fermentation process?

Answer 10

They stick to the yeast membrane

Question 11

At what ABV do natural yeasts tend to die?

Answer 11

15-15.5%

Question 12

How much CO2 is produced from 1hL of must?

Answer 12

4.5hL

Question 13

What is the most widely used strain of lab made yeasts?

Answer 13

Saccharomyces

Question 14

What are 3 features of lees contact?

Answer 14

• Higher acid
• More texture
• Complexity of aromas (brioche, toast, bread, butter)

Question 15

What is the definition of alcoholic fermentation?

Answer 15

The transformation by yeasts and sugars contained in grape must into ethyl alcohol and carbon dioxide

Question 16

What is chaptalization?

Answer 16

Adding sugar during the fermentation process to increase potential alcohol

Question 17

What are the two main forms of chaptalization?

Answer 17

1. Sugar
2. Rectified concentrated grape must (RCGM)

Question 18

What are some physical signs of alcoholic fermentation?

Answer 18

• 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

Question 19

What are some physical signs of alcoholic fermentation?

Answer 19

• 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

Question 20

What are some chemical signs of alcoholic fermentation?

Answer 20

• Conversion of glucose to ethanol
• Creation of other alcohols (sometime, e.g ethanol, methanol)
• High ethers (aromatic molecules)
• CO2 release

Question 21

How much does CO2 is produced per gram of sugar?

Answer 21

1/4 litre of CO2