It would seem obvious that wine is gluten-free. Wine is made by fermentation, with yeast transforming grape’s sugars into alcohol. Both grapes and yeast are gluten-free. But, there’s more to modern winemaking than fermentation alone. It’s not totally inconceivable that trace amounts of gluten could be introduced. 

Additives, barrel-aging and clarification have been highlighted by some articles as potential sources for gluten contamination. This article looks at each of those to see how much of a risk that really is.

Additives

It is possible to make wine without any additives whatsoever. However, these days, many wines have something added to enhance fermentation, stabilize the wine and/or add flavor. Here are common wine additives:

• Acid: Malic, tartaric or citric acid may be used to balance wines from warm regions.
• Anti-foam: A silicon oil, used in tiny amounts, to reduce foaming during fermentation
• Calcium Carbonate: Reduces acidity
• Diammonium Phosphate: A yeast nutrient which can support fermentation
• Dimethyldicarbonate: An anti-microbial that also reduces SO2 and ensures fermentation is fully stopped.
• Glycerine: Adds body and sweetness
• Grape Concentrate: This is added to some commercial wines to increase color, sweetness and/or alcohol.
• Gum Arabic: Hardened sap from acacia trees and consisting largely of sugars and proteins, it’s a stabilizer, binder and fining agent.
• Lysozyme: An enzyme taken from egg whites which inhibits bacteria and malolactic fermentation
• Oak Chips: If a wine won’t be aged in oak, chips may be added (and later removed) to add flavor and tannin.
• Pectinase: An enzyme that breaks down pectin within plants. In winemaking it both clarifies the wine and aids in extraction of color and juice.
• Sugar: Adding sugar prior to fermentation increases potential alcohol.
• Sulfur: The most widely used additive, it is an anti-bacterial and anti-oxidant.
• Tannins: These are naturally occurring in grape skins, stems, seeds and barrels. Winemakers may add tannin powder to balance ripe, red wines.
• Water: Adding water before fermentation reduces sugar by volume and, thus, potential alcohol.
• Yeast: Winemakers may add yeasts to ensure a successful fermentation.

The list above doesn’t include all possible additives for standard wines, but covers the vast majority. All of those additives are gluten free.

Use of Wheat Flour to Seal Wine Barrels

Paste made from wheat flour is a traditional sealant for barrel heads. The paste isn’t used between staves; the hoops ensure a tight enough fit. If there are trace amounts of gluten on the inside of the barrel due to use of this paste, it is very likely they would be washed away during steam cleaning prior to use of the barrel. Second-use or older barrels will be even less likely to contaminate wine, as the first batch of wine and subsequent steam cleaning would probably clear it away.

To see what gluten might find its way into wine from barrels, Tricia Thompson of Gluten Free Watchdog LLC conducted tests on bottled wines which had undergone lengthy aging in first-use wine barrels known to be sealed with wheat paste. Two different types of tests were run. In both cases, the results were in the lowest range. Gluten, if any existed, was below the detection threshold.

While this indicates gluten contamination of wine through wheat paste may be negligible, that was just one set of tests and is therefore anecdotal. If you are really concerned about gluten content, you might look for wines which have been neither fermented nor aged in wheat paste-sealed barrels. 

Fortunately, the paste is being used less and less. Wax is used instead. Unfortunately, winery websites don’t get into that level of specificity, so you’d have to ask them by phone or email.

If you don’t want to take any chances at all, steer clear of barrels. There are many wines which are fermented and/or aged in concrete or stainless steel. Neither of those introduce any gluten.

Clarification

Clarification removes floating particles from wine, including grape solids, proteins and yeast. Most high-volume and/or widely distributed wines are clarified. It reduces the risk of spoilage and consumers find hazy wines less appetizing. There are three basic levels of clarification: racking, fining and filtration. 

Racking is the least rigorous. It’s essentially like decanting, allowing the wine settle for an extended period and then carefully draining or siphoning it into another vessel without stirring up the sediment.

Fining is the next level of clarification and involves adding a powder or liquid to the top of the wine vessel. As the additive drifts to the bottom, it collects particles, proteins, etc. and carries them to the bottom as well. Since fining requires adding something, it’s theoretically possible gluten could be introduced. In practice though, that isn’t the case.

Here are the most common fining agents. None of them contain gluten.

• Chitosan: Made from shells of shellfish and insects
• Copper Sulfate
• Diatomaceous Earth: Very fine, calcium-rich earth
• Egg whites
• Gelatin: Proteinaceous and usually derived from beef or pork, but sometimes fish
• Gum Arabic
• Inactivated Yeast
• Isinglass: A proteinaceous substance made from fish
• Liquid Carbon: A solution containing carbon powder
• Pectinase
• Polyvinylpolypyrrolidone: A manufactured, chemical compound
• Potassium Caseinate: made from skim milk
• Silica Gel
• Silicon Dioxide
• Sodium Bentonite: A clay, typically mined from volcanic ash deposits

The most thorough method of clarification is filtration. Wine is passed through plastic or metal screens and/or pads made of paper or cloth. Filter screens and pads are all gluten-free. And the filter pads are actually fine enough to filter out most glutens along with other impurities.

Summary

The fermentation of grapes and their juice into wine is a gluten-free process. Odds of gluten finding its way into wine through other processes are extremely low. Common wine additives and fining agents are gluten-free. There’s a very slight chance gluten may be introduced by barrels, but there is no risk from stainless steel or concrete.

To be absolutely sure you're buying gluten-free wine, buy those which have been filtered and which have not seen any time in barrels. Some wineries are also certified gluten-free. This guarantees no gluten protein or modified gluten protein has been added and gluten content in the final wine is less than 20 parts per million.

JJ Buckley guest blogger Fred Swan is a San Francisco-based wine writer, educator, and authority on California wines and wineries. His writing has appeared in The Tasting Panel and SOMM Journal. Online, he writes for his own site, FredSwan.Wine (formerly NorCalWine), PlanetGrape, and GuildSomm. He teaches at the San Francisco Wine School. Fred’s certifications include WSET Diploma, Certified Sommelier, California Wine Appellation Specialist, Certified Specialist of Wine, French Wine Scholar, Italian Wine Professional, Napa Valley Wine Educator and Level 3 WSET Educator. In 2009, he was awarded a fellowship by the Symposium for Professional Wine Writers. In that same year, he was inducted into the Eschansonnerie des Papes, the honorary society of the Chateauneuf-du-Pape AOC.