Malolactic Bacteria

WLP675 Malolactic Cultures
Malolactic Fermentation is the conversion of malic acid to lactic acid by bacteria from the lactic acid bacteria family.  Lactic acid is less acidic than malic acid, which in turn decreases acidity and helps to soften and/or round out some of the flavors in wine.

These liquid cultures are available in vials to inoculate 6 gallons or 1 liter sizes to inoculate 60 gallons.

Please note: We recommend caution with using WLP675 with wine kits, which contain potassium sorbate and effect the viability of malolactic bacteria. Under FAQ questions below, you will find instructions for using WLP675 with wine kits.

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 30˚C. 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 55˚F or 12˚C), and high alcohol percentages (up to 15% alcohol by volume).


The SO2 tolerance = 10ppm

Best Before

The “best before” date is approximately 6 months after testing and packaging by White Labs.


Adding 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’s pressed from the skins or after it’s 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 doesn’t 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 doesn’t produce much in the way of flavor components that would be noticeable in wine.  

Best before dates

Q: The WLP675 Malolactic vial I purchased has been expired by 5 months. I have a one 6 gallon fermenter of Cab Sav at 8 brix. Would this malo still be okay to use?

I have a second vial with the same date -- should I use both in the same 6 gal fermenter in case they are "probably " viable but possibly getting weak? Can too much be used?

A: The malolactic vial is quite a bit past its expiration date. We usually give it about a 6 month window upon packaging for maintaining proper viability levels. This vial could be at best, 11 months old. If you cannot purchase a new vial that has not expired, the only way you can know for sure if the bacteria is still viable is to make a small starter with the vials. To do this, use 1-2 liters of apple juice with ~0.5 g of yeast extract and sterilize it by boiling. Place into a sanitized container with a lid, cover and let cool down to room temp. Add your vial to this in as sterile a manner as you can, replace the cap tightly and let grow for 5-7 days in a warm place. After this period, if you shake it up and pressure starts to build in the container, you know you’ve got growth. If not, the culture would not have been viable.

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

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.

Which quantities to buy?

Q: I plan on doing my malolactic fermentation in five gallon carboys and racking into larger barrels after the fermentation. Should I purchase the 1-liter amount or vials and propogate?

A: 1 liter is good for 100 gallons, otherwise you can use one vial in each 5 gallon carboy. If you want to propagate, you would use the 1:10 step up ratio to attain 650-750mls of malolactic culture (that would be 2-3 vials into 650-750mls for one week).