To make a long story almost irresponsibly short, at one time, most American whiskey entered the barrel at drinking proof, somewhere around 50% alcohol. After Prohibition, regulations were changed in a way that ultimately encouraged distillers to use a higher barrel entry strength, up to 125 proof, or 62.5% ABV. For more about the historical context of these changes in barrel entry proof, check out Michael Veach’s excellent narrative on his blog.

Why does this matter? Because differences in the barrel entry proof of whiskey make a big difference in how it tastes, and have significant repercussions for distillery operations.

Read more here