Yes, wine is a fermented food. It meets the formal scientific definition established by the International Scientific Association for Probiotics and Prebiotics (ISAPP), which defines fermented foods as “foods made using desirable microorganisms that change the properties of the food components.” Wine is produced entirely through microbial transformation of grape juice, making it one of the oldest and most widely consumed fermented products in the world.
Why Wine Qualifies as Fermented
Fermentation is the core process that turns grape juice into wine. Without it, you’d just have fruit juice. The transformation happens in two stages, both driven by living microorganisms.
In the first stage, yeasts consume the sugars in grape juice and convert them into alcohol and carbon dioxide. The earliest yeasts to appear reflect the diversity of species naturally living on the grape skin at harvest, including species like Hanseniaspora, Candida, and Metschnikowia. As fermentation progresses, hardier species take over. The dominant wine yeasts belong to Saccharomyces cerevisiae and Saccharomyces bayanus, the same family of yeasts used in bread and beer.
Many wines undergo a second fermentation called malolactic fermentation, where bacteria convert a sharp-tasting acid (malic acid) into a softer one (lactic acid) plus carbon dioxide. This is what gives many red wines and some whites their rounder, smoother mouthfeel. The process is driven by lactic acid bacteria, most commonly Oenococcus oeni. Nearly all red wines and a significant portion of white wines go through this step.
What Fermentation Creates in Wine
Fermentation doesn’t just produce alcohol. The microbial activity fundamentally reshapes the chemistry of grape juice, generating hundreds of compounds that weren’t there before. Yeasts break down large polyphenol molecules into smaller ones with stronger biological activity. This is why wine’s antioxidant profile differs substantially from that of plain grape juice, even though both start from the same fruit.
Fermentation also produces melatonin in wine, a compound better known for its role in sleep regulation. Melatonin levels peak between the first and second days of yeast activity, and both the primary yeast (Saccharomyces cerevisiae) and the malolactic bacteria (Oenococcus oeni) contribute to its production. The choice of yeast strain matters: wines made with non-commercial or indigenous yeasts tend to have higher overall polyphenol content, including higher levels of specific antioxidants like quercetin and kaempferol.
Does Wine Still Contain Live Microbes?
This is where wine diverges from fermented foods like yogurt or kimchi. While those products are typically consumed with active cultures still alive, most commercial wine goes through steps designed to reduce or eliminate microbial life before bottling.
Sulfur dioxide, the preservative listed as “sulfites” on wine labels, has a significant impact on lactic acid bacteria. Wines made without sulfites maintain stable populations of around 100,000 colony-forming units per milliliter. Adding sulfites after malolactic fermentation suppresses these bacteria, though the effect can be temporary. After about five months of aging, lactic acid bacteria often regrow even in sulfited wines. Interestingly, sulfite management has minimal impact on yeast and acetic acid bacteria populations.
Sterile filtration at bottling is the more decisive step. Cross-flow filtration can remove virtually all microorganisms, leaving wine microbiologically stable in the bottle. But not all wines are sterile filtered. Unfiltered and minimally processed wines can retain substantial microbial populations. Research from UC Davis found that barrel-aged wines typically contain 1,000 to 10,000 colony-forming units per milliliter by the end of aging. One Bordeaux wine bottled in 1949 was found to contain four million colony-forming units per milliliter when tested decades later. A 1926 vintage still had about 2,000 viable yeast cells per milliliter when examined 80 years after bottling.
That said, dairy products like yogurt and kefir still far outpace wine in probiotic potential. The sulfites added to most commercial wines are lethal to many strains of beneficial lactic acid bacteria, significantly reducing the diversity and quantity of live cultures compared to traditional fermented dairy.
How Wine Compares to Other Fermented Foods
Wine sits in the same broad category as yogurt, sauerkraut, kimchi, miso, kombucha, and sourdough bread. All are made through microbial transformation of a raw ingredient. The key differences are practical ones:
- Alcohol content. Wine’s fermentation produces significant ethanol, typically 11 to 15 percent by volume. Most other fermented foods produce trace amounts or none at all. ISAPP acknowledges this directly, noting that “some fermented foods contain alcohol.”
- Live cultures at consumption. Yogurt and kimchi are typically eaten with active microbes still present. Most commercial wine has been filtered or treated to minimize live organisms. Sourdough bread is similar to wine in this respect, as baking kills the microbes that created it.
- Bioactive compounds. Each fermented food generates a unique set of metabolites. Wine’s distinctive contribution is its concentration of transformed polyphenols, compounds that become more biologically active through fermentation than they were in the raw grape.
Natural and Unfiltered Wines
If you’re interested in wine specifically for its fermentation-related properties, the style of winemaking matters enormously. Natural wines, which use minimal or no sulfites and skip sterile filtration, retain far more microbial life than conventional bottles. These wines are closer in character to other living fermented foods, with active populations of yeast and bacteria still present when you drink them.
Conventional wines that are sterile filtered and preserved with sulfites are still fermented foods by definition. The fermentation happened, and the chemical transformation it produced remains in the bottle. But the living microbial component is largely gone. Think of it like the difference between fresh sauerkraut from a farmers’ market and a shelf-stable jar that’s been pasteurized. Both were fermented. Only one still contains live cultures.