Reductive Winemaking

Question 1

3 Main objectives for Reductive wines

Answer 1

1. Expression of varietal fruit character
2. Enhance freshness and vibrancy
3. Absence of 2 factors: oak and microbial spoilage

Question 2

Reductive wine making is suitable for 4 main things

Answer 2

1. Aromatic white wines
2. Also used for wines not known to be very aromatic
3. Red wines made to be consumed young
4. Warm climate red wines with light structure

Question 3

What is the Redox potential

Answer 3

Ability to gain electrons

Question 4

Oxidizing agents vs. reductive agents

Answer 4

Oxidizing agents have a positive redox potential
Reductive agents have a negative redox potential

Question 5

3 aspects of Reductions

Answer 5

1. Loss of oxygen
2. Gain of hydrogen
3. Gain of Electrons

Question 6

3 aspects of oxidation

Answer 6

1. Gain of oxygen
2. Loss of Hydrogen
3. Loss of electrons

Question 7

What is glutathione

Answer 7

It is a tri-peptide, being a natural antioxidant that blocks oxidation mechanisms. It is naturally present in grapes and is produced and released by yeasts during lysis. (Another positive effect of lees aging).

Question 8

What is sparging?

Answer 8

introduction of stripping gas, usually nitrogen, introduced in fine bubbles. The oxygen moves from the wine to the bubbles and then in 6 seconds is transfered to the atmosphere.

Question 9

What are all of the antioxidants that can be added to the wine? (4)

Answer 9

1. Ascorbic Acid and erythorbic acids
2. Glutathione
3. Tannins
4. Biological antioxidants (Yeast cells)

Question 10

Addition of Ascorbic acid and how it works

Answer 10

It reacts with oxygen to form hydrogen peroxide, which can then react with SO2. It must be used with free SO2 to scavenge Hydrogen peroxide.

Question 11

Are yeast cells highly oxidative or reductive?

Answer 11

Highly reductive

Question 12

Rules for temperature for reduction (3 concepts)

Answer 12

1. Cold temperature: more oxygen dissolved, but oxidation reactions are slower
2. Warm temperatures: less oxygen dissolved, reactions are faster
3. Best strategy is to exclude oxygen and keep temperatures low

Question 13

5 basic rules for grape and must handling

Answer 13

1. Work fast
2. Work cold
3. Protect the Juice
4. Low phenol extract
5. Clarify the juice

Question 14

5 basic rules for fermentation for a reductive wine

Answer 14

1. Neutral or enhancing yeast
2. Rapid initiation of fermentation
3. Ferment cold
4. Consistent and complete fermentation
5. Minimise sulphide production

Question 15

Importance of using neutral or enhancing yeast

Answer 15

We want to use neutral yeasts when we have an aromatic or semi-aromatic variety. We can use enhancing yeast when we have a neutral variety. Neutral strains do not dominate varietal character - lower ester production. We want to work with yeast strains that can release bound aroma precursors

Question 16

What can we do for a rapid initiation of fermentation

Answer 16

We need active and healthy yeast. And it is good to prepare a starter so that the yeast can be in the best condition as oxygen is needed for the production of sterols.

Question 17

Importance of fermenting cold

Answer 17

It is necessary for the retention of fruit characters and we want to ferment around 10-15 C

Question 18

4 Basic rules for stabilization and preparation for bottling

Answer 18

1. Remove yeast and add antioxidants
2. Minimize operations, exclude air, and remove oxygen
3. Keep cold bottle quickly
4. Monitor oxygen

Question 19

Why do we need to remove the yeast and add antioxidants

Answer 19

We need to remove the yeast as too much can promote sulphide. And we need to add SO2 and Ascorbic acid