UNIVERSITY PARK — Making wine is a complex endeavor — it depends on grape composition, microbes like yeast, and environmental conditions such as temperatures, rainfall amounts and soil quality where grapevines are growing. Traditionally, researchers conduct pilot-scale fermentations of about 5 gallons to evaluate things like grape quality or yeast behavior, but they take time and money. However, a new study by a team of researchers led by Penn State food scientists has shown that a quicker, cheaper option called microvinification — fermentations of 50 milliliters, about a quarter cup — is reliable and convenient for studying wine chemistry.

“With proper replication — doing enough repeated tests — microvinifications can give trustworthy results,” said study senior author Misha Kwasniewski, associate research professor of food science in the College of Agricultural Sciences. “These small-scale tests can be a powerful, cost-effective way to improve research accuracy, predict how wine will turn out based on grape chemistry and support commercial wine-production decisions.”

Results from this study, published in the American Journal of Enology and Viticulture, may open some eyes in the wine industry, Kwasniewski suggested, because microvinifications often are avoided due to concerns about high variability in results, too much oxygen exposure and other potential issues. He said this reluctance motivated him — along with study first author Ezekiel Warren, doctoral degree student in the Department of Food Science — to test whether these concerns are valid by closely examining oxygen exposure and how factors like temperature during fermentation and grape skin management affect wine chemistry in small-scale fermentations.

The researchers detailed measurements of oxygen uptake; phenolic compounds, which affect color, mouthfeel and bitterness; and aromatic compounds, which contribute to smell and taste, in both microvinifications and 5-gallon pilot-scale fermentations. They reported that the quarter-cup fermentations were consistent and did not suffer from too much oxygen, which could cause problems during fermentation and have a negative effect on wine quality.

The researchers found that variables such as temperature; cap management, referring to how grape solids are mixed; and maceration time, referring to how long grape skins are in contact with juice, did affect the outcome in microvinifications — just as they do in larger fermentations. The chemical profiles produced in microvinifications were very similar to those from pilot-scale batches, Kwasniewski said.

The researchers experimented with both Chambourcin and Noiret grapes in both the microvinifications and pilot-scale fermentations, although Kwasniewski said the grape varieties used in the research was not a critical concern since they were testing the scale not grape quality. Grapes used in both size fermentations came from the same areas of vineyards and were prepared in the same way: de-stemmed, hand crushed and yeast added.

“This is looking at wine making in a new way — there are wineries and wine researchers who really think the only way you can do anything that’s going to be relevant to wine is at scale,” he said. “So, if they’re going to make 10,000 gallons of it, we’ve got to do every trial at 10,000 gallons, which obviously makes progress difficult, cumbersome and expensive.”

There’s the product-improvement aspect of microvintifications to consider as well, Kwasniewski pointed out.

“As winemakers, we make all sorts of little interventions — such as harvest timing, adding specific cultured yeast strains or filtration — to get the best quality out of our products, and we must be able to accurately judge the results,” he said. “And microvinifications allow us to more easily accomplish that. But the practice has  rarely been used because of the prejudice against it in the industry. This study supports the idea that very small wine fermentations — just 50 milliliters or about a quarter cup — can be scientifically valid. It turns out, they’re not more prone to problems like oxygen exposure, and they can mimic larger batches well — making them a practical option for researchers and winemakers alike.”

Alex Fredrickson, fermentation consultant at Terroir Consulting Group, Portland, Oregon, contributed to the research. He was a doctoral degree student advised by Kwasniewski at the University of Missouri.

The research was funded by U.S. Department of Agriculture’s National Institute of Food and Agriculture.