Technique

It’s Lysozyme Time

Home winemakers have an important new resource in the ongoing battle against spoilage organisms — it’s called lysozyme. Discovered in the 1920s and used for decades in the pharmaceutical, dairy and cheese industries, this natural protein has come into increasing use in the wine industry in the past decade. It’s now available in home-scale quantities, giving amateur winemakers a means of reducing sulfite use while still protecting the health of their wines.

Lysozyme is an enzyme found in the protective fluids (tears, saliva and mucus) of most animals. Commercial lysozyme is isolated from egg whites. Lysozyme kills certain types of bacteria by attacking their cell walls. It’s effective against most eubacteria, but not against archaebacteria or eukaryotes. (Eubacteria are “ordinary” bacteria; archaebacteria are thermal-vent bacteria and their relatives. Eukaryotes include animals, plants, protists and fungi, including yeast.)

Lysozyme works against a range of lactic-acid bacteria that can affect wine stability, including Oenococcus, Pediococcus and Lactobacillus, all of which produce off-odors in wine. Lysozyme also kills Leuconostoc, the bacteria responsible for transforming malic acid into lactic acid during malolactic fermentation. It does not interfere with yeast.

Lysozyme can “clean up” batches of wine infested with unwanted lactic bacteria. It is increasingly used in a preventive mode, to stop problems before they can start. Lysozyme is also used to delay or prevent malolactic fermentation, an important consideration for some white wines. It also aids the stability of wines that are bottled without filtration and could therefore be subject to bacterial action in the bottle.

In home winemaking, sanitation issues can be difficult to control, accurate testing may be hard to come by and sterile filtration is virtually impossible. So lysozyme has great potential. It provides a terrific alternative to sulfite additions, particularly for delaying or preventing malolactic fermentations in white wines, which always requires threading a needle between too little (leading to an unwanted malolactic fermentation) and too much (leading to the nose burn of over-sulfited wines). Within recommended ranges, lysozyme has no discernible sensory impact on wine aroma or taste, and leaves no toxic residue. All of which led one home winemaker colleague of mine to extol lysozyme as a “magic bullet.”

For the record, lysozyme is not omnipotent and it by no means eliminates the need for sulfite additions. First of all, lysozyme does nothing to prevent oxidation and browning; for this, sulfur dioxide is still required. Similarly, lysozyme is no help against many of the nasty organisms on the winemaker worry list — such as Acetobacter, the vinegar bacteria, or Brettanomyces and other rogue yeasts — that require some combination of SO2 and sterile filtration. Finally, there are even some strains of lactic acid bacteria, including certain malolactic bacteria, which are resistant to lysozyme, and can only be controlled with sulfites or sterile filtration.

Here are some guidelines and suggestions for lysozyme use.

Preparation: To prepare the enzyme, add one part lysozyme (in powdered or crystalline form) to 5–10 parts tepid water. Stir gently, as shaking or rough mixing will produce foam and “gumballs.” Allow time for the lysozyme to dissolve completely, then add to wine or must, stirring gently with a sanitized utensil.

Timing and dosage: It’s up to you to decide whether to use lysozyme as insurance at every step along the way, or simply use it for known problems or intentional stylistic decisions. The effective dosage varies with the size of the bacterial population and the tannin level of the wine, so the numbers below are given as ranges.

For translating the ranges below, adding 100 parts per million (ppm) means 0.1 gram of lysozyme for each liter of wine (or 0.013 ounce per gallon); 250 ppm means 0.25 g/L (or 0.033 ounce/gallon). Even though it mixes measuring systems, my rule of thumb is that one gram per gallon is a hair over 250 ppm.

At the crush: Add 50–150 ppm lysozyme to red grape must or white grape juice. The lysozyme addition should be made after any addition of SO2, to allow the SO2 to diffuse and bind. Used this way, lysozyme will inhibit lactic acid bacteria and delay the onset of malolactic fermentation, thereby reducing any competition with the yeast for nutrients during the alcoholic fermentation.

Stuck fermentations: For red wines, add 150–400 ppm lysozyme. For whites, add 300–500 ppm, then restart fermentation with a new yeast culture. Stuck fermentations with rapid lactic acid bacteria buildup are great breeding grounds for volatile acidity. Fighting the lactic acid bacteria with heavy sulfite additions can also inhibit yeast fermentation activity, keeping it stuck. In contrast, lysozyme targets the bacteria and lets the yeast do its thing.

Preventing malolactic: Once primary fermentation is complete, malolactic activity can be blocked with an addition of 250–500 ppm of lysozyme. This dosage will also stop a malolactic fermentation in progress, resulting in a partial malolactic conversion. For wines that received a small lysozyme treatment at the crusher, inoculation with a malolactic starter should work normally after the alcoholic fermentation has run to completion.

Aging stability: For wines that go through a malolactic fermentation, wait until this fermentation is complete, then add 250–500 ppm of lysozyme to prevent lactic acid bacterial activity during aging.

Bottling: For unfiltered or lightly filtered wines that have not already been treated with lysozyme, an addition of 250–500 ppm can be done a few weeks before bottling for greater stability. In the bottle, free SO2 becomes bound and less effective over time. Lysozyme’s effectiveness decreases at a slower rate.

In all these situations, lysozyme does its work in about a week or ten days, at which point testing or further treatment can be done.

Blending: Blending different wines means that lysozyme treatment has to be reconsidered, or perhaps redone. For example, if a malolactic white wine is blended with another non-malolactic wine, the resulting blend will need a lysozyme addition to remain stable. If the stylistic goal is a partially malolactic-fermented wine, mixing batches in this way is probably the most practical method. It offers more control than starting a malolactic fermentation, then stopping it, in a single batch. The same is true if a treated wine receives a significant amount of topping with a wine untreated with lysozyme.

Testing: In a commercial setting, lysozyme treatments are accompanied by several rounds of testing: to determine which problem bacteria are present, and in what numbers; to determine if any resistant strains are present, requiring different treatment; to make sure the killing action worked and the bacteria are eliminated; and to determine if a malolactic fermentation happened according to plan.

For home wineries, testing for malolactic activity should at least be done. (In my book, bottling anything without knowing its malolactic status is a serious leap of faith.)

If testing indicates that a lysozyme addition has not prevented malolactic activity, the problem may be a resistant bacterial strain and sulfite control may be the only option. With stuck fermentations, testing could determine the lactic bacterial load and therefore indicate the appropriate lysozyme addition. However, if a fermentation is truly stuck, and testing isn’t available, don’t be afraid of lysozyme additions at the upper end of the ranges above.

Clarification and fining: Because lysozyme is a protein, it can contribute to protein haze in some wines when they are stored at warmer temperatures. Its killing action can also result in some precipitation of the lees. Precipitation, if it does appear, normally shows up in a few days and the wine can simply be racked for clarification. Be cautious and allow at least a couple weeks between a final lysozyme addition and bottling.

Fining: Bentonite neutralizes enzymatic activity, including that of lysozyme. The same is true for carbon fining agents, oak chips and high tannin levels. Yet for good heat stability, and the prevention of cloudiness, bentonite may need to be part of your winemaking routine.

For non-malolactic wines, treat with lysozyme first to kill bacteria, then fine with bentonite later — but remember that the killing power of the lysozyme has been greatly reduced. A light second addition of lysozyme can serve as insurance. For reds and whites that do go through malolactic, fine with bentonite after fermentation is complete, then treat with lysozyme later for barrel and bottle stability.

The same logic applies to oak chip additions. Let the lysozyme have two weeks to kill malolactic bacteria; test to make sure; add oak chips for whatever duration is appropriate; rack the wine off the chips and then protect the wine with a second treatment.