Whether it's wine or any other alcoholic beverage, drinks with excessively high alcohol content are often difficult to consume. While there are spirits with extremely high alcohol levels in the world, for wine specifically, the upper limit for enjoying wine as it should be is probably around 12-13% for white wines and 14-15% for red wines.
On the other hand, attention to low-alcohol wines has been growing even stronger recently. Non-alcoholic wines are being sold worldwide and are beginning to gain popularity. We're increasingly seeing non-alcoholic wines appear on winery product lists these days. We also hear opinions like "I love wine, but if I could enjoy the same taste and aroma without alcohol, that would be preferable." Creating wines without raising the alcohol content too much is becoming one of the techniques that winemakers should definitely know.
There are several methods for reducing wine's alcohol content. Some require large-scale equipment, while others involve simple approaches like diluting with water. Not everything is possible due to laws in various countries, but the options available to winemakers are increasing.
As new technologies emerge, there are also techniques that were verified in the past but are no longer discussed today. One such technique is the method using an enzyme called glucose oxidase. There are good reasons why technologies fall out of favor, but today we'll focus on this particular technique.
What is Glucose Oxidase?
Glucose oxidase (GOX), as its name suggests, is an enzyme with the specific property of oxidizing and breaking down glucose, also known as grape sugar. Various microorganisms are said to be capable of producing this enzyme, but industrially, those produced by the black koji mold (Aspergillus niger) seem to be used most frequently.
This enzyme is utilized as a natural biosensor for measuring glucose concentration, as well as for many familiar applications such as removing sugar from eggs, preventing discoloration in potato chips and french fries, and preventing oxidation of animal fats, meat, and fruits.
Incidentally, the fact that honey doesn't spoil easily is also related to this enzyme. Honey contains this enzyme, which works to reduce oxygen from the air into hydrogen peroxide on honey's surface. This hydrogen peroxide acts as an antibacterial agent, protecting honey from spoilage. Glucose oxidase is also a natural preservative.
The Role of Enzymes in Winemaking
In sake and beer brewing, enzyme use is essential for the "saccharification" process, which converts the starch in rice and malt into glucose. In winemaking, however, you might not hear enzyme names mentioned as often. This doesn't mean that enzymes aren't used in wine production facilities. In wine brewing, an enzyme called pectinase is very commonly used. Moreover, for yeast to produce alcohol from grape sugars in the first place, enzymes produced by the yeast are necessary. Even in winemaking, though it's not conspicuous, enzymes are actually inseparable from the process.
Why Does Wine's Alcohol Content Decrease?
Why can using GOX reduce wine's alcohol content? The mechanism is quite simple. This enzyme converts glucose, which serves as the raw material for alcohol, into gluconic acid, which is not a sugar but an acid.
Yeast metabolizes the sugars contained in grape juice into alcohol. At this time, glucose is particularly favored and consumed by yeast. Glucose is the primary raw material for yeast to produce alcohol.
On the other hand, GOX converts glucose into something other than sugar before yeast can take it up, so yeast becomes unable to absorb glucose. From the yeast's perspective, the raw material has disappeared, so it cannot produce alcohol. Since GOX doesn't produce alcohol from glucose, the wine's alcohol content decreases as a result.
Half of the sugars contained in grape juice are glucose. Therefore, theoretically, the amount of alcohol that can be reduced through GOX treatment is approximately 50%. However, since GOX cannot actually break down all glucose, verification results report that reductions of up to about 40% were possible compared to untreated cases.
The Mechanism and Conditions for GOX Breaking Down Glucose
The reaction by which glucose oxidase breaks down glucose in grape juice proceeds in two stages.
In the first step, β-D-glucose is oxidized to D-glucono-1,5-lactone. At this time, hydrogen peroxide is simultaneously generated. GOX functions as a catalyst for oxidizing this β-D-glucose. In the subsequent step, D-glucono-1,5-lactone is hydrolyzed to gluconic acid, but this reaction is not enzymatic, and strictly speaking, GOX is not involved in the reaction.
To obtain low-alcohol wine through GOX treatment, GOX must act on glucose at an earlier stage than yeast in the brewing process. Therefore, the fundamental prerequisite for GOX treatment is processing the juice. Furthermore, for GOX to work more efficiently, high pH and elevated temperature are required. The optimal environment for this enzyme to work efficiently is said to be pH 5.5-6.0 and temperature 30-40°C.
However, merely adjusting pH and managing temperature is still insufficient to maximize this enzyme's utilization. Oxygen supply is absolutely essential.
Glucose oxidase is an enzyme that performs aerobic reactions. Its reaction efficiency depends not only on glucose concentration in the target material but also on oxygen concentration. No matter how well environmental conditions like pH and temperature are arranged, the reaction hardly proceeds under anaerobic conditions. Speaking specifically about winemaking facilities, juice to which GOX is added must be deacidified in advance to raise pH, and considerable aeration must be performed during the enzyme's reaction time. This is one reason why GOX use isn't promoted in winemaking.
The Unavoidable Oxidation of GOX Treatment
Implementing aeration is essential to achieve sufficient results with GOX treatment. When sufficient aeration was performed after enzyme addition, the alcohol content of the finished wine dropped to nearly half, whereas when sufficient aeration wasn't performed, there was only a slight decrease of about 0.7%. On the other hand, juice oxidation caused by this aeration has also been identified as a factor in quality deterioration of the finished wine. Specifically, browning of color and effects on sensory evaluation of taste and aroma have been reported.
The alcoholic fermentation process, essential to winemaking, is conducted under extremely anaerobic conditions. Since yeast metabolizes sugars in grape juice and expels alcohol and carbon dioxide, the grape juice during fermentation contains almost no oxygen. This allows previously oxidized juice to recover to some extent. Past verification reported that juice oxidized by GOX treatment recovered approximately 40% of its condition through alcoholic fermentation. However, conversely, this means 60% remains oxidized.
As a result, sensory evaluation of the finished wine showed weaker fruit flavors and shorter aromatic finish compared to untreated wine. It's also known that acidity increases due to the influence of gluconic acid generated as a result of the enzymatic reaction.
The aeration performed in GOX treatment brings results similar to hyper-oxidation in some ways, but the amount of oxygen introduced differs significantly. Consequently, GOX treatment causes oxidation not seen in hyper-oxidation.
Additionally, it's known that juice oxidized by enzyme treatment requiring excessive aeration, or wine made from such juice, requires larger amounts of SO2. This is due not only to juice oxidation but also to significant effects from hydrogen peroxide and carbonyl compounds generated during treatment. These substances have properties that bind strongly with SO2, naturally increasing the amount of SO2 that needs to be added to wine.
Summary: Why You Need to Know About GOX
Wine's low-alcohol technology is currently one of the most watched technical fields. Approaches aren't limited to brewing aspects; various attempts are being made from cultivation perspectives as well. The background also involves various factors.
What's been strongly emphasized recently is the improvement in grape ripeness due to global warming accompanying climate change. In some regions, grapes have begun ripening early to levels called over-ripeness. Fully ripened grapes contain large amounts of sugar. More sugar becomes raw material for producing more alcohol, and wine alcohol concentration continues to show an upward trend.
On the other hand, what's been discussed for decades already is alcohol's health effects. In a world where people's health consciousness is strengthening, wines with lower alcohol content continue to be sought. For those who drink wine at lunch meetings, to avoid interfering with afternoon work, and for drivers, to avoid interfering with driving, demand for wines with low alcohol content or containing no alcohol at all is by no means small. Furthermore, from an industrial perspective, such technologies are sometimes noted as ways to avoid tax rates based on alcohol content.
Despite increasing attention to these technologies, the method using the enzyme glucose oxidase has been ignored as if completely forgotten. No verification papers of any kind have been published in recent years.
The reason is clear. The drawbacks are significant, including excessive oxidation accompanying treatment and the resulting wine quality deterioration. Additionally, since this involves using an enzyme not naturally contained in grapes, national-level approval is required for use, which also has no small impact.
On the other hand, I personally believe that methods utilizing this enzyme have brewing advantages that are by no means small. In a sense, these are things that can only be achieved because of this enzyme. Having knowledge about this enzyme is meaningful when considering such application methods.
The specific content of the application methods I envision can be found in articles included in the online circle or magazine. Those interested should consider joining the circle or subscribing to the magazine.