Malolactic Fermentation

Grapes contain three acids: Citric, Malic and Tartaric. Malolactic fermentation (MLF) is a process in winemaking in which tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Many red wines benefit from a malolactic fermentation. Chardonnays also get that buttery taste from a malocatic fermentation.

We recommend malolactic fermentation on fresh juices rather than wine kits which contain potassium sorbate and effect the viability of malolactic bacteria.

Here are many FAQs from White Labs (our source for Malolactic culture) website:

General Instructions

Wait for fermentation to reach a gravity of approximately 5 Brix, towards the end of fermentation. Warm culture to room temperature and inoculate must. If one inoculates at the beginning of fermentation, the yeast and WLP675 could compete for resources and may cause a stuck fermentation. To determine the completion of the MLF (malolactic fermentation), monitor the depletion of malic acid. The accepted value for a completed MLF is around 30ppm. Inoculations larger than 59 gallons To inoculate larger volumes, we recommend inoculating with a larger culture. If time is not an issue, one can propagate the bacteria to larger volumes, but keep in mind that malolactic bacteria is a slow-growing, fastidious organism. Depending on the size of the propagation, it could take weeks to grow. Propagation Instructions White Labs recommends allowing 7 days for tenfold growth. The best media for propagation is apple or grape juice (or must, if available), supplemented with fructose, malic acid, and nutrients such as that contained in MRS broth. Approximately 2% of the total volume of media can be composed of finished wine, in order to acclimate the bacteria to alcoholic conditions. We recommend an incubation temperature of 73F. More information on propagation can be found under FAQ questions below. Optimal pH The optimal pH is approximately 4.0, but WLP675 will handle a pH of 3.3 in red wines and 3.1 in white. Additional Information WLP675 has a high tolerance to low pH (3.0), low temperature environments (down to 55F, and high alcohol percentages (up to 15% alcohol by volume). SO2 The SO2 tolerance = 10ppm

Potassium metabisulfite

Q: If I use your cultures to induce Malolactic fermentation after the primary, is it okay to still use potassium metabisulfite prior to the start of alcoholic fermentation to kill the wild yeast? If so, should I use less than normal (50mg/L)?

A: Yes, you can still add the metabisulfite as you normally would. The amount that is used at the beginning to inhibit the wild yeast will eventually dissipate once fermentation begins so it will not affect the malolactic fermentation that occurs later on.

Sulfite Tolerance

Q: What sulfite level will Malo tolerate?

A: The amount of free SO2 should be at 10mg/L or less in order for the Malolactic to survive.

Using Malolactic in conjunction with wine kits

Q: We are a winery and we use wine kits. The info on your website mentions that you do not recommend use of this type of fermentation with the wine kits because the kits use potassium sorbate. My question is this: the potassium sorbate is added at the stage of clarification and stabilization. If I do not add the potassium sorbate until after the MLF is complete (or not at all), is it o.k. to use this process with the wine kit? How long does MLF take?

A: The Malolactic can be added successfully, if the potassium sorbate is added after completion. Malolactic fermentation usually takes 4-6 weeks to finish (30ppm malic acid).

Are additional nutrients needed?

Q: I wanted to know if any nutrients are needed for using the WLP675 Malo bacteria culture. My retailer offers no special nutrients for this product, and I would like to know what is needed, if anything.

A: There are no nutrients needed for WLP675, although adding yeast extract or a complete yeast nutrient can help aid the MLF.

Minimum temperature

Q: What is the minimum temperature that I need to maintain for WLP675 Malolactic?

A: 60F is the recommended low, however this strain can tolerate down to 55F.

When do I add Malolactic?

Q: Do you add WLP675 Malolactic bacteria to wine before it is pressed from the skins or after it is pressed? Also, if the sugar level (brix) is 0, is it bad for the skins to remain in contact with the juice while the bacteria settles in?

A: The bacteria should be added before pressing, at around 5 Brix. If the wine is already down to 0, it should be okay for a few days with the Malo added without adversely affecting the finished wine.

What occurs if added after pressing?

Q: I am an amateur wine maker. My local wine shop suggested that I try your Malolactic cultures. I crushed cabernet grapes and fermented them for 7 days. Your instructions make it sound like I should have added it to the must and let it ferment longer before pressing the must. Please let me know if I have done this wrong.

A: It is best to add the Malo before pressing so that the bacteria will have some sort of nutrients to work with. If the culture is added after pressing, it may just take a little longer to begin MLF, but should be enough to take off (although slowly). In addition, adding yeast extract or a complete yeast nutrient can help the fermentation be successful, even after pressing.

Malolactic & Filtering:

Q: Can WLP675 Malolactic tolerate the action of racking the wine or running it through a filter with a mechanical impeller type pump?

A: It can tolerate the filter, depending on the filter size. If it is larger than .2 micron, it should still be able to flow through the filter.

Propagating Malo in larger quantities

Q. You were very helpful last year when I had some questions about my White Labs bacteria and I wanted to ask a few more questions as the grapes are soon here. I plan to purchase 5 vials of the WLP675 and propagate the bacteria to satisfy 100 gallons of Cab/Merlot/Cab Franc blend. For propagation, should I use 1/4 distilled water, 3/4 apple juice and make a 500ml batch and then split it? This is what you suggested when I used only 2 vials. Will I need to add more than a 1/4 tsp of malic acid?

A. If you plan on using the 5 vials to propagate, I would recommend using a larger juice batch at least 1 liter. In this case, you would also need to double your addition of malic acid. If your propagation media volume is too small, you could risk competition for nutrients between the bacteria, resulting in lower cell growth.

Mouth feel, aroma and taste

Q: Can you tell me what affects it has on mouth feel, aroma and taste and whether it produces significant amounts of volatile acids or biogenic amines?

A: It does not produce significant amounts of either. Because it converts malic acid to lactic acid, it reduces the harsh, astringent mouth feel that can sometimes be present in new red wines. In general, it rounds out the flavor characteristics of the wine, but it does not produce much in the way of flavor components that would be noticeable in wine.

When to add the malo?

Q: Is 5 brix the surest sign to know the best time to add the malo?

A: The 5 Brix is a rule of thumb that we recommend, but the malo will work fine in a wider range than that.

Source White Labs



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