There is a lot of answer to that question. A century ago would have been 1914 and most alcohol businesses were fighting Prohibition and losing.
More than 150 years ago, Pasteur and germ theory were the turning point, but there are ancient texts that supposed there were unseen causes of disease. Still, brewers knew that clean equipment made better beer, even if they couldn't explain why.
The very act of fermentation kills pathogens. Pathogens are too fastidious to survive fermentation of even a half percent of alcohol.
What's left is various flora that survive fermentation or are introduced later. In the 1600's and 1700's, yeast was considered an acid that split sugars into alcohols, but if left too long would split alcohol into vinegar. This made it important to skim fermenting beer of dark krausen. In that era, "fresh" beers were termed "mild" while older casks showing Brett and souring were described as "hard." It was common to ask for a blend of mild and hard beers to suit your taste, since there generally wasn't more than a handful of choices (usually sorted by alcohol strength), in that era.
With the industrial revolution came more efficient Cornish engines (early 1800's). The use of excess steam to scald equipment and kegs came into fashion because it provided efficient cleaning. The additional sterilization was an unanticipated benefit.
Mundane equipment cleaning was done with various soaps and lye, plus plain ol' hard scrubbing.
Prior to getting steam, breweries would burn "brimstone matches," aka sulfur sticks, in casks and fermenters. It was actually someone's job to sniff the bunghole in order to separate sweet from sour.