Bubbly Boozy Beets
Some of the beets that we canned had bulging lids, when they were opened they were pressurized and carbonated. They reeked like booze. The brine was vinegar and sugar and some pickling spice, no salt. I think that salt would have helped slow or stop the fermentation. The jars may also have been packed too tight. Craziness.
Technically, a brine isn’t a brine unless you add salt to it. What you had was a pickling liquid. Vinegar has natural fermentation properties, and sugar feeds that. Salt will inhibit it. You can get away with a saltless pickle when it is refrigerated, but at room temp, no way.