Yeast And Wine

Question 1

Yeasts have two different Metabolisms

Answer 1

Fermentative Metabolism –> Ethanol –> 2 ATP
2. Respiratory Metabolism –> Biomass (no ethanol) –> 36 ATP

Question 2

ATP

Answer 2

The principal molecule for storing and transferring energy in cells.

Question 3

Respiration and glycosis

Answer 3

During the glycolysis, glucose is broken down to produce 2 molecules of 3 carbons, the pyruvate.

Question 4

YEAST REHYDRATION & ACCLIMATION

Answer 4

During the phases of rehydration and acclimation, the respiratory metabolism should be pushed by increasing the amount of dissolved oxygen (DOT) and avoiding high concentrations of sugar, which would stimulate fermentation due to the Crabtree effect.

Question 5

Acclimation

Answer 5

• The cell senses the environment via protein molecules on its surface, i.e. the cell membrane.
• A proper acclimation procedure allows a stepwise contact between the yeast population and a new environment, grape must in our case. This procedure stimulates the growth even in the early phases of fermentation, thus reducing the length of the lag- phase.

Question 6

What happens with no oxygen during ferm

Answer 6

If however no oxygen is present in the environment, yeast degrade pyruvate by converting it into ethanol.

Question 7

Crabtree Posititve

Answer 7

Certain yeasts possess the ability to produce ethanol even in presence of oxygen !!!
Yeasts demonstrating this phenomenon are characterised as Crabtree-positive.

Question 8

Crabtree positive yeast (3)

Answer 8

Saccharomyces cerevisiae
1. Ferment sugar in addition to respiration
2. In presence of oxygen
3. Above a critical [sugar]

Question 9

Crabtree negative

Answer 9

However, not every yeast exhibit this phenomenon. Therefore, yeast consuming sugar only under the respiration pathway are characterised as Crabtree-negative.

Also they use solely the respiration pathway

Question 10

What kind of yeasts can we use in Wine Making

Answer 10

Crab-tree Positive yeasts

Question 11

Four phases of Yeast

Answer 11

1. Lag Phase
2. Exponential Phase
3. Stationary Phase
4. Death Phase

Question 12

Lag phase

Answer 12

Respiration doesnt stop completely

Question 13

Exponential Phase

Answer 13

Respiration stops

Question 14

Stationary Phase

Answer 14

To control the number of
living cells, methilin blue can be used
to color dead cells.

Question 15

Death phase

Answer 15

If too many cells die, fermentation will stop

Question 16

3 Most common yeast

Answer 16

1. Metschnikowia pulcherrima
2. Saccharomyces bayanus
3. Saccharomyces cerevisiae

Question 17

Saccharomyces bayanus

Answer 17

More capable to overcome osmotic pressure,
used in sparkling wine making. Used for wines
made from very sweet grapes.

Question 18

Metschnikowia pulcherrima

Answer 18

Very famous. It is a yeast that is able to respire,
it is able to get a lot of flavors. Used in production of aromatic grapes. It has the enzymatic pull
able to cut flavor precorsurs

Question 19

Active Dry Yeasts (ADY)

Answer 19

dried yeast culture, with a humidity lower than 8%, with a granted number of live cells higher than 1010 UFC/g and with a maximum number of yeasts belonging to different species lower than 105 UFC/g.

Question 20

Active dry yeast (4)

Answer 20

1. Allows complete fermentations
2. Minimizes the production of off-flavors related to the fermentative activity(H2S, volatile acidity, etc.)
3. Technological features which are more suitable to specific types of winemaking processes and/or wine styles
4. Allows a greater repeatability of the process and
   products which are more constant year by year

Question 21

Which are the best features for a winemaking yeast? (Fermentative attributes) (5)

Answer 21

• Quick start for the fermentation
• Total consumption of sugar
• Ethanol tolerance
• Wide range of temperature
• Low nutritional requirements

Question 22

Which are the best features for a winemaking yeast? (Aromatic attributes) (5)

Answer 22

• Low production of Volatile Acidity
• Good Production of secondary aromas
• Release of primary aromas
• Good production of glycerol
• Low production of H2S

Question 23

Which are the best features for a winemaking yeast? (Technological Attributes) (5)

Answer 23

• Resistance to Copper ( And other inhibitors)
• Production of Glutathione
• Production of Mannoproteins
• Demalicating action
• Acidifying action

Question 24

3 – Technological characteristics: special yeasts

Answer 24

1. Antioxidant Action - Protects white wines from oxidative damage (browning, loss of aroma).
2. Demalicating Action - Lowers the overall acidity of must without producing lactic acid.
3. Acidifying Action - Enhances the acidity of musts with high content of sugar and low content of acids.

Question 25

Two breeding techniques for Yeasts

Answer 25

Sexual and Asexual