I made a 5 gallon mash (pilsener and a little Crystal 60, OG 1.065) and split it into two 2 1/2 gallon batches, hopped one with Simcoe and the other with Amarillo for IPAs (both around 75 IBU). Added a 1.5 liter 1056 starter, split between the two. Things seemed to be going fine for two weeks, then I added an ounce of hops to each one for dry hopping. After a day, the Amarillo smelled very strongly of cider vinegar, although the hop aroma is evident as well. The next day the Simcoe batch smelled that way too. These don’t smell a little off, it’s a very strong odor.
Is there any chance that this is anything other than an infection?