Investigating the Effects of Oak Spiral Aging on Beer ABV and IBU

Prior studies have identified a decrease in ABV and an increase in IBU associated with oak spiral aging in beers. Initial results indicated that the ABV decrease was because of oxidation of ethanol to acetic acid due to resealing of bottles, while the IBU increase was proposed to be due to oak components that dissolved in aged beer. In this study, commercial beer samples were opened, allowed to sit for 30 seconds and resealed. Additionally, an oak spiral was added to a 5.00 % aqueous solution of ethanol. After three weeks, there was no difference in ABV or acetic acid content in the opened bottles when compared to bottles that remained sealed. The oak spiral ethanol solution exhibited a decrease in ABV similar to that found in our prior studies. Both UV-Visible spectra and A275 absorbance of this same solution indicate that oak spirals contribute a significant amount of absorbance at 275 nm thus confirming that oak components contributed to the IBU increase. In conclusion, oak spirals do appear to decrease beer ABV in an oxidation-independent fashion while concomitantly increasing IBU values using the A275 IBU method.