Beer, wine, cider, sake and the soreness of the body after an intense workout—these outcomes are all the result of one biochemical pathway found in oxygen-dependent organisms: fermentation.

The Fermentation Science program out of Oregon State University’s Department of Food Science and Technology focuses on educating students on the delicate process of creating fermented products such as beer and wine. 

According to Dr. Alan Bakalinsky, an associate professor in the department, the key ingredient to creating a fermented alcoholic product is yeast.

“Yeast is essential in the process of winemaking,” Bakalinsky said. “If there’s no yeast, there’s no wine. The yeast converts grape juice into wine.”

According to Bakalinsky, the yeast converts sugars present in the grape juice into alcohol, carbon dioxide and other compounds. Concurrently, it is also growing and reproducing.

Yeast, however, is not producing alcohol and other compounds for human consumption, according to Bakalinsky.

“The way to think about it is that the yeast is doing this not to make wine, but to grow,” Bakalinsky said. “Fermentation is a process by which microorganisms obtain energy. It’s not a particularly efficient way to gain energy, but it works.”

According to Dr. Chris Curtin, associate professor of food science and technology, certain microbial strains are used specifically for either wines or beers. One such yeast is Brettanomyces, which has adverse effects in wine, but is desired in certain types of beer. However, there is a chance for crossover of wine- or beer-specific yeasts during the process if the fermenter deems so, Curtin added.

“While Brettanomyces is considered spoilage in wine, if you want to make a farmhouse ale or a Belgian style beer then you actually want Brettanomyces,” Curtin said. “That’s kind of what drew me to working here was looking at the flip side.”

According to Curtin, the main differentiation between wine and beer yeasts and bacteria centers around the fuels they metabolize. 

“The main thing that separates brewers ale yeast from wine yeast is in the types of sugars they might eat,” Curtin said. “A wine yeast will happily ferment and make beer. But it’s going to be over-attenuated, making for a very dry beer.” 

Brewers can control the presence and concentration of microbes in the process or leave it open to the atmosphere, according to Curtin. The process of opening a fermentation product to a local microbiome is referred to as spontaneous fermentation. 

“You can ferment really wild or partly wild,” Curtin said. “Really wild would be letting as many species as possible all go for it. You might start off with that situation, but if you start adding SO2 in a wine fermentation context then you are going to reduce the diversity and you’re gonna have a simpler fermentation.” 

According to Curtin, sulfur dioxide can be added to the mixture, reducing any harmful or unwanted bacteria. This practice is also seen in wine.

A fermenter creating wine may want to kill off spoilage microbes with sulfuric oxide, but other strains and species are incredibly important to the process, according to Bakalinsky. One such strain is the Saccharomyces cerevisiae yeast. 

Bakalinsky’s specialty is working with the Saccharomyces cerevisiae yeast, a naturally occurring yeast found in vineyards globally. The subsequent propagation of this yeast through winemaking and brewing activities allowed early humans to master these microbes in spite of the fact that they had no microscopes to observe them with, according to Bakalinsky. 

“It was all discovered by accident,” Bakalinsky said. “It was our great fortune that this yeast is present in vineyards and the environment where grapes grow naturally. So there’s no need for human intervention. Unharvested grapes will ferment (or rot in a similar process) in the vineyard. Our ancestors had no idea about the true cause of the fermentation process, but over time they nonetheless developed a deep practical understanding which has led to a thriving global wine industry.”

Regardless of yeast strain or processing techniques, these products are linked by one common factor, the fermentation pathway, according to Bakalinsky. 

“It depends on the substrate you start with,” Bakalinsky said. “If you start with fruit juice, you get wine. If you start with malted barley, you get beer. If you start with honey, you get mead. If you start with rice, you get sake. But all of the yeasts involved in converting these starting ingredients into alcoholic beverages are very closely related yeasts.”

Jared Johnson, a graduate student in the Food Science and Technology program, studies non-traditional wine yeasts known as non-Saccharomyces yeasts, which also naturally occur on the fruit. 

“Non-Saccharomyces are naturally present on the surface of the grape. Some of them can be present in really high numbers,” Johnson said. “So they can hugely contribute to the wine. In some situations it can be a positive contribution, in some they are considered spoilage organisms.”

According to Johnson, the Saccharomyces yeast takes a non-intuitive pathway to create energy. 

“The thing is that using oxygen in your metabolism like how we do is more energetically favorable, you end up producing more ATP, more energy by using oxygen,” Johnson said. “But for some reason Saccharomyces decides not to do that, even when oxygen is abundant. The term is ‘crabtree positive,’ and it means that Saccharomyces will grow fermentatively in the presence of oxygen, as long as sugar concentrations are sufficiently high.”

According to Johnson, fermentation may be advantageous for Saccharomyces because it has a faster metabolic process than aerobic respiration. This results in a faster consumption of glucose, which is then converted eventually to ethanol, which is a potentially toxic substance to other types of organisms. 

According to Johnson, he sees a shift in winemaking to include more non-Saccharomyces yeasts. 

“I actually originally came here to study beer, but switched to wine because I wanted to study these non-traditional organisms that can contribute during fermentation,” Johnson said. “I think there’s gonna be a big shift, and you’re already starting to see it in the beer world where they are starting to using these non conventional yeasts and other microorganisms to produce unique beer or similarly, kombucha.”

Saccharomyces yeast and fermentation processing can be manipulated to create flavors and aromas, according to Johnson. Scientists are investigating how non-Saccharomyces yeasts contribute to the palette as well. 

A common misconception is that brewers and winemakers transfer in flavor notes derived from flowers or citrus fruits during the fermentation, according to Bakalinsky.

“It’s probably confusing for a lot of people when they hear a wine described as having hints of citrus and rose and lavender and leather and so forth as though wine makers are adding those flavors,” Bakalinsky said. “None of those flavors are added, they’re all derived from the grape, from the yeast and from the processing steps.” 

Other fermentative processes being explored at the food science and technology department include mead, kombucha and cider, according to Curtin. In regards to cider, Curtin places it approximately in between wine and beer fermentation practices.

“Similar to winemaking, you’re taking a fruit and crushing it,” Curtin said. “Once you’ve got the juice, it’s separated by how it’s treated. The cider maker might make their product like a brewer or a winemaker.”

Other disciplines such as creating mead come with its own set of challenges, according to Johnson. 

“From my understanding, one of the major differences between mead production verses beer and wine, is that mead does not naturally contain high amounts of the nutrients needed to carry out a healthy fermentation,” Johnson said. “This is especially true for nitrogen, which act as building blocks for enzymes and other components of cellular growth. For this reason, nitrogen must be added to the mead to avoid problems like sluggish fermentation.”

Mead makers must add nitrogen to their substrate in order to get yeast to grow, a process that may cause problems such as slow fermentation, according to Johnson.

“The sugars in general are pretty accessible, it’s the nitrogen in particular,” Johnson said. “Because honey doesn’t have it. That is one of the main challenges.”

According to Curtin, another separating factor between beer, wine and cider is whether pasteurization is part of the process. Pasteurization involves heating the product to the point where potentially harmful or spoilage microbes are killed. This is performed with beer processing and sometimes with ciders, but never with wine; instead, winemakers use sulfur oxide, Curtin added.

“In winemaking, if you add sulfur dioxide, again that’s going to influence the microbiome,” Curtin said. “It’s going to kill off sensitive species and strains. Some are more tolerant.”

Through the years, brewing techniques have changed with culture and technology, according to Curtin. Old brewing techniques are making a resurgence in present day.  

“There’s been a bit of resurgence in traditional beer styles, lots of barrel-aged beers, farmhouse ales,” Curtin said. “So that’s where you have the beer wort and you put it in a coolship and then let whatever is around inoculate it.”

Most of the time, a cold ship is housed in a room with other brewing vessels such as barrels, according to Curtin. The atmospheric microbiome associated with whatever room it is housed in will inoculate the fermenter product, creating a unique local taste.