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advances in enology > Yeast And Wine > Flashcards

Yeast And Wine Flashcards

1
Q

Yeasts have two different Metabolisms

A

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

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2
Q

ATP

A

The principal molecule for storing and transferring energy in cells.

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3
Q

Respiration and glycosis

A

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

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4
Q

YEAST REHYDRATION & ACCLIMATION

A

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.

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5
Q

Acclimation

A
  • 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.
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6
Q

What happens with no oxygen during ferm

A

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

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7
Q

Crabtree Posititve

A

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

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8
Q

Crabtree positive yeast (3)

A

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

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9
Q

Crabtree negative

A

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

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10
Q

What kind of yeasts can we use in Wine Making

A

Crab-tree Positive yeasts

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11
Q

Four phases of Yeast

A
  1. Lag Phase
  2. Exponential Phase
  3. Stationary Phase
  4. Death Phase
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12
Q

Lag phase

A

Respiration doesnt stop completely

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13
Q

Exponential Phase

A

Respiration stops

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14
Q

Stationary Phase

A

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

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15
Q

Death phase

A

If too many cells die, fermentation will stop

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16
Q

3 Most common yeast

A
  1. Metschnikowia pulcherrima
  2. Saccharomyces bayanus
  3. Saccharomyces cerevisiae
17
Q

Saccharomyces bayanus

A

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

18
Q

Metschnikowia pulcherrima

A

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

19
Q

Active Dry Yeasts (ADY)

A

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.

20
Q

Active dry yeast (4)

A
  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
21
Q

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

A
  • Quick start for the fermentation
  • Total consumption of sugar
  • Ethanol tolerance
  • Wide range of temperature
  • Low nutritional requirements
22
Q

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

A
  • Low production of Volatile Acidity
  • Good Production of secondary aromas
  • Release of primary aromas
  • Good production of glycerol
  • Low production of H2S
23
Q

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

A
  • Resistance to Copper ( And other inhibitors)
  • Production of Glutathione
  • Production of Mannoproteins
  • Demalicating action
  • Acidifying action
24
Q

3 – Technological characteristics: special yeasts

A
  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.
25
Q

Two breeding techniques for Yeasts

A

Sexual and Asexual

advances in enology (19 decks)

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