Temperature control

Question 1

Why is it important to keep freshly picked grapes cool

Answer 1

cooler temperatures delay the onset of oxidation and also slow or stop microbial spoilage. It will also stop spontaneous fermentation from the ambient (yeast shut’s down around 4C)

Question 2

How would you chill whole bunches?

Answer 2

In a refrigeration unit. It is a slower process than heat exchange.

Question 3

Why would you pick a heat exchanger over a refrigeration unit for chilling partially crushed grapes?

Answer 3

Because a heat exchange needs liquid to work effectively. It’s a quick process, but wouldn’t work on whole bunches.

Question 4

At what temperatures are fruity white wines usually fermented?

Answer 4

15C

Question 5

For a more savoury, less fruit driven white wine, what temperature range would you aim to ferment at?

Answer 5

17-25C

Question 6

What will the temperature of the must naturally do during fermentation?

Answer 6

Go up. Fermentation is a living process, therefore heat is given off. The chemical reaction is :
sugar + yeast + oxygen = alcohol + heat + CO2

Question 7

With warmer temperatures, what happens to the volatile aromas in wines

Answer 7

They tend to get swept away with the CO2. They are very light, so a lower temperature, slower fermentation will preserve them. (It’s important to note that they won’t last long in relative terms - fruity wines should be drunk within a year to make the most of the fruit flavours)

Question 8

What is a standard temperature for fermentation of fruity, low tannin red wine?

Answer 8

20C

Question 9

For a wine with greater levels of tannin and extraction, what temperature might you expect the fermentation to take place at?

Answer 9

30C

Question 10

How come red wines can have higher temperatures than whites for fermentation?

Answer 10

The Polyphenols present in reds protect against oxidation, so they can tolerate higher temperatures.

Question 11

What is the benefit of reducing the temperature at the end of the fermentation for red wine?

Answer 11

It will reduce the extraction of tannin, which is much more easily dissolved in alcohol. The warmer the ferment, the more extraction. Therefore if the temperature was not checked at the end - when there is the highest proportion of alcohol, the extraction of tannins would increase significantly.

Question 12

What temperature range would you expect for rosé fermentation?

Answer 12

12-16C - cooler temperature as the retention of fruity flavours is important. Most rosés are designed to be drunk within a year. The flavour profile desired is low-med alcohol, med-high acidity, plenty of fruit.

Question 13

How would you grow grapes with higher acidity in a warmer climate?

Answer 13

• Plant at a higher altitude
• Pick a slope with an aspect that is not full sun. A slope that faces into the morning sun will be cooler than a slope that gets afternoon sun.
• Pick earlier. The risk of this option is that the aromas and flavours might not be fully developed.

Question 14

How can you maximise solar radiation in a cool climate

Answer 14

• Aspect: a vineyard on a slope will have a favourable angle for catching maximal solar radiation in a cool climate
• Orientation: East will allow for morning sun to dry the dew and warm the soil, and reduce the risk of fungal infection. South (S, SE, SW) facing slopes will increase sun exposure and slightly advance budburst, thus extending the ripening season.
• Water: a body of water will reflect the heat and light back onto the vineyard, increasing the overall radiation exposure.
• Canopy management: ensure the grapes are not overshadowed, but keeping enough leaves to help the plant photosynthesise.

Question 15

At what temperature does budburst occur

Answer 15

10C

Question 16

What is the ideal temperature range for photosynthesis (think of t-shirt weather)

Answer 16

18-33C

Question 17

What is the temperature range for fruit set (think of childbearing age)

Answer 17

26-32C

Question 18

At what temperature do acid levels stop decreasing during ripening

Answer 18

15C

Question 19

What is the ideal temperature range for anthocyanin synthesis (higher education - get your colours!)

Answer 19

15-22C

Question 20

What is the ideal temperature in the last month of ripening for rapid acid level decrease?

Answer 20

> 21C

Question 21

For every 100m, what is the loss in temperature?

Answer 21

0.6C

Question 22

What is the cycle frequency of El Niño?

Answer 22

3-7 years