Wine and Protein | Managing Causes of Haze and Allergies

Wine contains protein. Many people are surprisingly unaware of this fact.

Some might say, "I know about that. Proteins are added as fining agents, right?" That's correct. However, wine also contains proteins that don't originate from fining agents.

One might think, "If drinking wine provides protein intake, that sounds healthy," but in winemaking, protein is a troublemaker. Unfortunately, there are almost no benefits to having protein present in wine.

This article examines proteins that can pose significant problems for wine, organizing information about their origins and management methods.

Origins Beyond Fining Agents

Fining agents are one major reason why wine contains protein, but they're not the only source.

Grapes themselves also contain protein.

There are various reasons why grapes contain protein. Research has shown that in some cases, grapes produce certain proteins as a defense mechanism against pathogenic organisms like fungi. The amount produced varies depending on grape variety, climatic conditions of the vintage, and the presence of pathogenic organisms they're defending against. Drought stress and the degree of rot are considered to have particularly significant impacts.

Additionally, when wine undergoes extended aging in containers with settled lees from finished fermentation, the yeast cells decompose. These decomposed yeast cells can also serve as a source of protein.

Two Reasons Why Protein Is Unwelcome in Wine

Reason 1: Allergenic Properties

One reason is that proteins are, broadly speaking, allergenic substances. Animal proteins commonly used in wine fining, such as casein and albumin, are classified as proteins requiring attention as allergens. From a consumer health perspective, some countries and regions already mandate labeling these proteins on wine labels.

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Reason 2: Wine Haze Formation

The second reason proteins are unwelcome is that they cause wine to become hazy. Proteins sometimes create a white, cloudy haze in wine. While this isn't as problematic in red wines, it can represent a serious quality defect in white wines, rosé wines, and sparkling wines.

Why Does Wine Become Hazy?

Think about making a fried egg. You crack an egg into a frying pan. The egg white is still transparent. Then, as heat is gradually applied, the white part becomes white, true to its name.

Egg whites (albumin) are precisely what's used as fining agents in wine, and their main component is protein. The reason egg whites turn white in fried eggs is due to the heat denaturation properties of protein. In wine, however, proteins bind with polyphenols and metals present in the wine to form colloids, which then precipitate out, becoming visible as a white, cloudy haze.

Incidentally, heat-induced protein precipitation does occur in wine, but when the reaction temperature exceeds 60°C, this becomes more problematic than the haze itself. If protein haze appears due to heat, such wine would be better used for mulled wine or other heated wine preparations.

While egg whites invariably turn white when cooked, the situation with wine is more complex. A high protein content doesn't necessarily mean haze will develop. Research shows that protein haze in wine depends on the types of proteins present and the wine's chemical composition, making it more or less likely to occur.

Protein Management in Winemaking

Ultimately, proteins present in wine are targeted for removal. However, during winemaking processes, proteins are sometimes intentionally added. Even in these cases, they are removed at the end.

The approach can be broadly divided into three cases:

1. Removing proteins naturally present in wine to prevent haze formation
2. Proactively adding proteins to bind with phenolic compounds also present in wine, causing them to precipitate, thereby preventing future haze formation from protein-phenol interactions
3. Adding proteins to remove phenolic compounds, regardless of future haze potential

The use method commonly known as fining agents corresponds to case 3 above. However, case 2 essentially accomplishes the same thing. The difference lies in the amount added. Note that in both cases 2 and 3, because residual added proteins are undesirable, protein removal treatment is typically performed after the addition treatment in most cases.

Methods for Protein Removal

Traditional Method: Bentonite

The most common method for removing proteins from wine uses a clay mineral called bentonite. This method has been practiced for ages, and bentonite still provides the highest protein removal efficiency. No alternative method has been found that surpasses it.

However, recent efforts have focused on finding alternatives to bentonite. The reasons include avoiding wine impact, losses, and disposal costs associated with spent bentonite. Candidates range from microfiltration and flash pasteurization to more obscure methods, but among these, enzyme utilization has attracted the most attention.

New Approach: Enzyme Utilization

The idea of using enzymes to break down proteins isn't inherently novel. Digestive enzymes work to help us absorb proteins consumed in our diet. The challenge lies in finding the right type of enzyme.

Various searches for enzymes to break down wine proteins have been conducted. Enzymes from the yeast Saccharomyces cerevisiae and from Botrytis cinerea, known as the causative agent of gray rot, have been tested. However, none showed promising results. This is because grape proteins have high resistance to these enzymes.

This situation has changed over the past decade. An enzyme capable of acting on the robust protein structures found in grapes has been discovered. This enzyme is called Aspergillopepsin (AGP).

Koji Fungi Gaining Attention in the Wine Industry

This AGP enzyme was actually discovered from Aspergillus niger, a black koji mold very familiar in Japan.

Enzymes from koji fungi are utilized in sake and shochu production. In these alcoholic beverages, koji fungi are grown directly on rice, the raw material, accumulating enzymes within the ingredient before mixing with sake rice for use. In wine, however, koji isn't grown on grapes; only the enzymes are utilized.

While this enzyme is derived from sources other than grapes, its use is already spreading, particularly in Australia, and the EU approved its use in 2021.

Characteristics of AGP

Advantages

AGP's advantage lies in its ability to remove wine proteins more efficiently than other enzymes. Unlike bentonite, it doesn't affect wine taste or aroma, and its use doesn't generate losses or secondary disposal costs.

Limitations and Challenges

However, more efficient utilization of AGP requires combination with short-time heating methods. Non-heated use limits protein removal rates to about 20%, while combining with heating methods increases removal rates to approximately 90%.

Even when combined with heating methods, AGP's final protein removal rate remains lower than bentonite's, and it's ineffective against some proteins, requiring bentonite co-treatment for their removal. Therefore, AGP cannot serve as a complete replacement for bentonite.

AGP utilization is more important when viewed not as a replacement for bentonite, but as a pretreatment to reduce bentonite requirements and associated wine impact, and as one long-term preventive measure after bottling.

Summary | How to Assess Protein Risk

While we've discussed the risk of wine haze when proteins are present in wine, how this risk is assessed varies considerably among individual winemakers. For example, the author always measures protein levels before bottling wine, but rarely performs bentonite treatment based on these results.

This isn't because no treatment is needed due to absence of proteins. In most cases, proteins are present to some degree. The decision not to treat comes from weighing wine impact from bentonite use against the risk of protein residue. Many winemakers make similar judgments.

However, this doesn't mean protein residue risk should be taken lightly. Except for certain wine categories, haze in white wines or rosé wines leads to complaints and potentially renders hundreds or thousands of bottles unsaleable. From a safety standpoint, protein removal treatment should be performed even if it means accepting some quality reduction.

Winemakers constantly struggle between their reluctance to intervene and the risks of not doing so.

In this context, AGP utilization—which, within tested parameters, doesn't affect wine sensory evaluation—represents a potentially groundbreaking preventive measure. Perhaps in the future, we might see AGP listed on wine labels instead of egg whites.

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