To help winemakers determine the best caps for their wine bottles, researchers at the University of California, Davis, are studying the performance — specifically the variability — within different types of closures.

Their goal is to determine whether consumers can taste the difference in wines that are bottled and capped exactly the same — a difference that could be attributed only to variation among each type of wine closure.

The researchers — including a wine chemist, a medical radiologist and a biomedical engineer — are evaluating 600 bottles of Sauvignon Blanc wine, each sealed with one of three different types of closures: natural cork, screw caps or synthetic cork. The study will monitor changes in the wine during aging, culminating in a sensory evaluation to determine if wine experts and consumers can taste the different levels of oxidation that occur in the wine due to variability within each type of closure.

Oxidation, or exposure to oxygen, is the most important factor in wine aging, according to wine chemist Andrew Waterhouse, a professor in the UC Davis Department of Viticulture and Enology. But too much oxidation can cause a loss of color, flavor and aroma.

“Our goal in this study is to determine if individual bottles might be getting a lot more or less oxygen — and therefore aging at different rates — as a result of the variation in the closures used to seal the bottle,” said Waterhouse, who is carrying out the study with UC Davis undergraduate student Jillian Guernsey.

“Ultimately, when all of the data are in, we won’t be declaring that one type of closure is superior to another. Rather we’ll be giving winemakers information about the variability of each type so that they can determine which is most appropriate for use in bottling their wines,” Waterhouse said. “If variation is high enough for consumers to notice a difference, we will work with the industry to help find ways to manage the variation so that consumers receive the wine as it was intended.”