Enzyme Activity in Wine: Natural and Added Enzymes

What Are Enzymes and Why Do They Matter in Wine?

Enzymes are biological catalysts, protein molecules that accelerate specific chemical reactions without being consumed in the process. In winemaking, enzymes play critical roles at every stage, from juice extraction and clarification to aroma release and color stability. Some are naturally present in grapes and yeast, while others are added by winemakers as commercial preparations.

Understanding enzyme activity helps winemakers optimize juice yield, improve clarity, enhance aroma expression, and manage color. Enzyme additions are among the most cost-effective interventions available, yet they remain underutilized by many home winemakers who are unfamiliar with their chemistry and application.

How Enzymes Work

Enzymes function by lowering the activation energy of a chemical reaction, making it proceed faster than it would spontaneously. Each enzyme has an active site that binds to a specific substrate (the molecule being transformed), forming an enzyme-substrate complex. After catalysis, the product is released and the enzyme is free to bind another substrate molecule.

Enzyme activity is influenced by temperature (activity increases with temperature up to a point, then the enzyme denatures), pH (each enzyme has an optimal pH range), substrate concentration (activity increases with substrate availability up to the enzyme's maximum rate), and the presence of inhibitors (substances that block or reduce enzyme function).

In wine, the relevant pH range is 3.0-3.8 and temperatures during processing range from 10-30°C. SO₂ can inhibit some enzymes, particularly oxidases. Ethanol also affects enzyme activity, generally reducing it at higher concentrations.

Natural Grape Enzymes

Polyphenol Oxidase

Polyphenol oxidase (PPO), also called tyrosinase, is the most important endogenous grape enzyme from a winemaking perspective. PPO catalyzes the oxidation of phenolic compounds (particularly caftaric acid and coutaric acid) to quinones, which then polymerize to form brown pigments.

PPO activity is highest immediately after crushing, when grape cells are disrupted and the enzyme comes into contact with its substrates in the presence of oxygen. This is why rapid sulfiting at crush is critical for white wines: SO₂ inhibits PPO activity and reduces quinones back to colorless phenolics, preventing browning.

PPO activity is destroyed by fermentation because ethanol denatures the enzyme. This means that once fermentation begins, PPO is no longer a concern. However, the oxidative damage done before fermentation can persist in the finished wine.

Laccase

Laccase is an oxidase enzyme produced by Botrytis cinerea, the mold responsible for both noble rot and gray rot. Unlike grape PPO, laccase is resistant to SO₂ inhibition and can oxidize a wider range of phenolic substrates. Laccase remains active even after fermentation, making it a persistent threat to wine quality.

Grapes infected with Botrytis carry laccase into the must, where it can cause severe and rapid browning, particularly in white wines. The only effective way to deal with laccase is to remove it, either through bentonite fining (which adsorbs the enzyme protein) or through flash pasteurization at 70°C.

Pectinases

Grapes naturally contain some pectinase enzymes, but their activity is generally insufficient for effective juice extraction and clarification. These endogenous pectinases begin breaking down pectin (a structural polysaccharide in grape cell walls) upon crushing, but commercial pectinase additions dramatically accelerate and complete this process.

Commercial Enzyme Additions

Pectinases: The Workhorse of Winemaking Enzymes

Pectinase preparations are the most widely used commercial enzymes in winemaking. Pectin is a complex polysaccharide that forms the "glue" holding grape cells together and contributes to the viscosity and haziness of grape juice. By breaking down pectin, pectinases improve juice yield, accelerate settling and clarification, and enhance extraction of color and aroma compounds trapped within grape cells.

Pectinases are a family of related enzymes including polygalacturonase (which cleaves the pectin backbone), pectin esterase (which removes methyl groups from pectin), and pectin lyase (which breaks the pectin chain through a different mechanism). Commercial preparations contain mixtures of these activities optimized for winemaking conditions.

For white wines, pectinase addition at crush improves juice yield during pressing and promotes rapid settling (debourbage), allowing cleaner juice to be fermented. For red wines, pectinase enhances color and tannin extraction by breaking down skin cell walls, releasing pigments and phenolic compounds more efficiently.

Glycosidases: Releasing Bound Aromas

Many grape aroma compounds exist as glycoside-bound precursors, in which the volatile aroma molecule is attached to a sugar that renders it odorless and non-volatile. Glycosidase enzymes cleave this sugar linkage, freeing the volatile compound and enhancing wine aroma.

The most important glycosidase targets in wine are terpene glycosides (releasing linalool, geraniol, and other floral compounds in aromatic varieties) and norisoprenoid glycosides (releasing beta-damascenone, TDN, and other complex aroma compounds).

Yeast naturally produce some glycosidase activity during fermentation, and acid hydrolysis slowly releases bound aromas during bottle aging. Commercial glycosidase preparations can accelerate this process, releasing bound aromas during or after fermentation. They are most beneficial for aromatic varieties like Muscat, Gewurztraminer, and Riesling.

However, glycosidase activity is inhibited by the low pH and high sugar content of grape must. These enzymes work best in finished wine with lower sugar and slightly higher pH. Some modern preparations have been specifically selected for activity at wine pH.

Lysozyme: An Enzymatic Antimicrobial

Lysozyme is an enzyme derived from egg whites that destroys Gram-positive bacteria by hydrolyzing their cell wall peptidoglycan. In winemaking, lysozyme is used to control lactic acid bacteria without relying solely on SO₂.

Lysozyme is effective against Oenococcus oeni, Lactobacillus, and Pediococcus, making it useful for preventing unwanted MLF in white wines or for protecting wines during the vulnerable period after primary fermentation when SO₂ levels may be low. It has no effect on yeast or Gram-negative bacteria (like Acetobacter), so it is a targeted antimicrobial rather than a broad-spectrum one.

The typical dosage is 250-500 mg/L. One limitation is that lysozyme is a protein and can contribute to protein haze in white wines, so it may need to be removed by bentonite fining before bottling. Winemakers must also consider that lysozyme is derived from eggs, which may require allergen labeling.

Beta-Glucanase: Improving Filterability

Beta-glucanase enzymes break down beta-glucans, polysaccharides produced by Botrytis cinerea that clog filters and make wine extremely difficult to clarify. Wines made from botrytized grapes (both noble rot and gray rot) often contain enough beta-glucan to make filtration practically impossible without enzymatic treatment.

Beta-glucanase is also useful during sur lie aging, where it accelerates the breakdown of yeast cell walls (which contain beta-glucan), promoting the release of mannoproteins and other autolysis products that enhance wine body and mouthfeel.

Enzyme Application in Practice

Dosing and Timing

Commercial enzyme preparations come with manufacturer recommendations for dosage and application timing. General guidelines include:

Pectinases should be added at crush for both white and red wines, at rates of 1-3 g/100 kg of grapes. Allow several hours (or overnight for white juice settling) before proceeding to the next step.

Glycosidases are best added during or after fermentation, at rates recommended by the manufacturer. Some preparations are designed for must, while others are optimized for finished wine.

Lysozyme should be added after primary fermentation if the goal is to prevent MLF, or at crush if early bacterial control is needed.

Temperature and pH Considerations

Most commercial wine enzymes are optimized for activity at 15-25°C and pH 3.0-3.8, which aligns well with typical winemaking conditions. Lower temperatures slow enzyme activity but do not destroy it, so cold-stabilization temperatures may require longer contact times. Very high temperatures (above 60°C) denature most wine enzymes.

SO₂ levels below 100 mg/L total generally do not significantly inhibit commercial enzymes, though very high SO₂ can reduce activity. Ethanol above 13-14% may also reduce enzyme effectiveness.

Avoiding Unintended Consequences

Some commercial enzyme preparations contain cinnamyl esterase activity as a side effect. This enzyme releases vinyl phenols from hydroxycinnamic acid precursors, which are the same precursors that Brettanomyces uses to produce 4-ethylphenol. While the enzyme itself does not produce Brett aromas, it liberates precursors that could amplify Brett character if the yeast is present. Look for commercial preparations certified as having low or no cinnamyl esterase activity.

Frequently Asked Questions

Do I need to add enzymes for home winemaking?

Enzyme additions are not strictly necessary, but they can significantly improve wine quality. Pectinase is the most valuable addition for home winemakers, improving juice yield, clarification speed, and extraction efficiency. It is inexpensive, easy to use, and beneficial for virtually all wines. Other enzyme additions (glycosidases, lysozyme) are more specialized and may not be needed for every batch.

When should I add pectinase?

Add pectinase at crush or at pressing for the best results. For white wines, add to the juice before settling; for red wines, add to the must before fermentation. Adding enzyme before fermentation gives it time to work on the pectin while the must or juice is still in contact with grape solids. Allow at least 4-12 hours for the enzyme to act before proceeding.

Can I add enzymes after fermentation?

Yes, some enzymes work effectively in finished wine. Glycosidases for aroma enhancement are often added post-fermentation. Beta-glucanases for improving filterability work in wine. Pectinases can be added post-fermentation to help with clarification, though they are most effective at the crush stage. Check the specific product's recommendations for optimal timing.

Do enzymes affect wine flavor?

Enzymes themselves do not directly contribute flavor, but they influence flavor by releasing aroma precursors (glycosidases releasing terpenes), improving extraction (pectinases releasing skin compounds), and removing haze-forming proteins and polysaccharides. When used correctly, enzyme additions generally improve wine quality and expression without introducing off-flavors.

Are enzyme additions considered "natural" winemaking?

This depends on the specific regulatory framework and philosophy. Many certified organic wine programs allow certain enzyme additions, while others restrict or prohibit them. The natural wine movement generally avoids all enzyme additions, relying on endogenous grape and yeast enzymes. Commercial winemaking uses enzymes widely and considers them standard processing aids rather than additives.