Oxidative Damage: Process & Prevention

Last Updated: 5/2022

Applies to: Winemakers looking to understand how oxidative damage occurs and how a variety of winemaking tools prevent it. This article offers options for preventing oxidation while reducing the use of SO2.

Oxidative damage in wine is responsible for browning, loss of varietal aroma, and bruised apple/sherry off-aromas. Ultimately these effects diminish wine quality and shorten shelf-life. Damage can occur when oxidation goes unchecked, triggering a series of reactions known as the oxidation cascade.

Damage can be prevented by disrupting the oxidation cascade. Sulfur dioxide is commonly used for this purpose, however other innovative enological tools can also be used. An understanding of the oxidation cascade is necessary to understand how all of these tools work.

The Oxidation Cascade

The process of juice and wine oxidation is often described as “the oxidation cascade” because it occurs as a string of reactions. Preventing oxidation involves limiting quinone formation and/or limiting the reactions quinones can participate in. The oxidation cascade can be classified into two main groups of reactions:

1. Quinone Formation - Grape phenolic compounds are converted to quinones.

Quinones can be produced from susceptible grape phenolic compounds in one of two ways: enzymatically or chemically. In the enzymatic mechanism, polyphenol oxidase enzymes (e.g., laccase and tyrosinase) convert susceptible phenols into quinones. In the chemical mechanism, oxygen reacts with transition metals like iron and copper to form radical oxygen species (highly reactive). These radical oxygen species can then oxidize susceptible phenols into quinones. The chemical mechanism is shown below:

2. Quinone Reactions - Quinones react with many compounds in juice and wine.

Quinones are highly reactive and can interact with many compounds in juice and wine (see Figure on the right). Some of these interactions cause oxidative damage (browning, off-aroma production, loss of varietal aroma, etc...).

  1. Browning occurs when quinones react with polyphenols in wine, producing brown pigments which are especially visible in white and rosé wines.
  2. Oxidative aroma production occurs via the Strecker degradation. In this reaction, quinones and amino acids interact to form aldehydes like methional and phenylacetaldehyde which have aromas of bruised apple and sherry.
  3. Quinones can trap aromatic thiols, resulting in a loss of wine varietal aroma.

Preventing Oxidative Damage

Preventing oxidation involves limiting quinone formation and/or limiting quinone reactions.

Sulfur dioxide (SO2) is commonly used to protect must and wine from oxidation. SO2 prevents quinone formation by inhibiting polyphenol oxidase enzymes. SO2 also prevents quinone reactions by directly binding with quinones and ensuring they cannot interact with other juice and wine compounds. However, SO2 can have a negative impact on wine sensory properties and can delay the onset of malolactic fermentation. Additionally, SO2 has been of particular concern to consumers desiring “low chemical input” wines.

Fortunately, there are several tools that can act as alternatives to SO2 in preventing oxidation including yeast derivative nutrients, tannins, and non-Saccharomyces yeast. These tools disrupt the oxidative cascade at different points:

GLUTASTAR™ is a yeast derivative nutrient rich in antioxidant peptides that react with quinones, limiting quinone reactions. GLUTASTAR was developed for its extreme antioxidant protection and contains a variety of antioxidant peptides including glutathione. Glutathione is a tripeptide that can exist in two forms: reduced and oxidized. Only the reduced form (glutathione sulfyhdryl or GSH) can interact with quinones and prevent them from participating in other reactions. Although GLUTASTAR is rich in GSH, it is more effective than GSH alone due to its unique profile of additional antioxidant peptides.

INITIA™ is a non-Saccharomyces yeast that rapidly consumes large amounts of oxygen and lowers copper levels, thereby limiting quinone formation. INITIA, a selected strain of Metschnikowia pulcherrima, consumes large amounts of oxygen to synthesize polyunsaturated fatty acids (PUFA) necessary for its cell membrane construction. M. pulcherrima contains approximately 100 times more PUFAs than Saccharomyces yeast, and unlike Saccharomyces yeast, cannot uptake PUFAs from the environment. Synthesizing PUFAs requires a significant amount of oxygen, leaving the environment oxygen depleted.

ESSENTIAL ANTIOXIDANT™ is a tannin that scavenges metal ions and quinones and inhibits laccase, disrupting the production of quinones and limiting the reactions they can participate in.

Choosing Antioxidant Products

While GLUTASTAR, INITIA, and ESSENTIAL ANTIOXIDANT all offer antioxidant protection, each have functions that differentiate them:

  • GLUTASTAR provides textural impact
  • INITIA provides microbial control prior to fermentation
  • ESSENTIAL ANTIOXIDANT combats laccase due to high Botrytis load and adds antioxidant protection during aging

Note: These products can be used in combination to maximize antioxidant properties and lower SO2 use throughout the winemaking process. However, these products do not completely replace the use of SO2 - GLUTASTAR and ESSENTIAL ANTIOXIDANT do not offer antimicrobial protection, and INITIA only offers antimicrobial protection prior to fermentation.