13.7 General Winemaking Options: Malolactic Conversion

Question 1

What is malolactic conversion?

Answer 1

• AKA malolactic fermentation, MLF, ‘malo’

- the result of lactic acid bacteria converting malic acid into lactic acid and carbon dioxide, produces heat

Question 2

When does malolactic conversion typically occur?

Answer 2

After alcoholic fermentation and occasionally during it.

Question 3

What conditions encourage malolactic conversion?

Answer 3

• 18–22°C (64–72°F)
• a moderate pH (3.3–3.5)
• low total SO2

Question 4

Historically, how did malolactic conversion kick off?

Answer 4

Often happened spontaneously in the spring following harvest as temperatures rose in the cellar

Question 5

Nowadays, how does malolactic conversion kick off?

Answer 5

Can be started by adding (‘inoculating with’) cultured lactic acid bacteria and making sure that the optimum conditions are available

Question 6

What conditions prevent malolactic conversion?

Answer 6

• temperature below 15°C (59°F)
• low pH
• moderate levels of SO2

Question 7

If a producer wants to ensure that malo does not occur, what can they do?

Answer 7

• add the enzyme lysozyme, which kills lactic acid bacteria
• move any batch of wine going through malolactic conversion to another part of the winery to avoid the spread of lactic acid bacteria
• lactic acid bacteria can be filtered out to avoid malolactic conversion taking place

Question 8

What types of wines go through malolactic conversion?

Answer 8

• Red wines routinely go through malolactic conversion

- It is a winemaker’s choice for white wines

Question 9

What are the 4 main outcomes of malolactic conversion?

Answer 9

1. Reduction in acidity and rise in pH
2. Some colour loss in red wines
3. Greater microbial stability
4. Modification of the flavour

Question 10

Why does MLF result in a reduction in acidity and rise in pH? In what types of wines may this be desirable? What is the end result?

Answer 10

• Lactic acid is a weaker acid than malic acid
• May be desirable in overly acidic wines (e.g. Chardonnay grown in a cool climate such as Chablis) but not in wines that are already relatively low in acidity
• It results in a softer, smoother style of wine

Question 11

In what types of wines is a loss of color OK?

Answer 11

Most reds except in very pale red wines

Question 12

How does MLF stabilize a wine? What is the flip side?

Answer 12

• If the wine goes through malolactic conversion during or after alcoholic fermentation, this then prevents malolactic conversion from spontaneously happening later (e.g. when the wine is in the bottle) when it would be undesirable.
• However, in cases where the pH of the wine is high, raising the pH slightly makes the wine more vulnerable to spoilage organisms and may create a wine that is not refreshing because the acidity will have been decreased.

Question 13

When a wine’s ph is high, why might MLF be undesirable?

Answer 13

Raising the pH slightly makes the wine more vulnerable to spoilage organisms and may create a wine that is not refreshing because the acidity will have been decreased.

Question 14

How does MLF affect the flavor a wine?

Answer 14

• slight loss of fruit character may occur
• addition of buttery notes (notably in white wine)
• increase volatile acidity

Question 15

What are the advantages of conducting MLF in small barrels as opposed to large tanks?

Answer 15

• the ability to be able to stir the lees at the same time

- promote better integration of the flavours

Question 16

What are the disadvantages of conducting MLF in barrels as opposed to tanks?

Answer 16

• more work because barrels may be at different temperatures and so will need monitoring individually.

Question 17

Why might a winemaker prefer to promote malolactic conversion at the same time as alcoholic fermentation?

Answer 17

• increase fruity characteristics (or alternately not detract from the final wines)
• reduce production times, saving money as wines can be finished and sold earlier