It's National Beer Day–the anniversary of the Cullen-Harrison Act of 1933, which—in the second decade of Prohibition in the U.S.—legalized beer and wine with an alcohol content of 3.2 per cent of lower in the U.S. It was one of the first important steps in the repeal of Prohibition.

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Several of the booze industry’s largest breweries have their roots in nineteenth-century companies. But between 1829—when Yuengling, the oldest American brewery still in operation, started producing booze—and today, there was a 13-year period where selling alcohol was illegal in all states.
“Prohibition crippled a thriving brewing industry in the United States,” writes Kate Vinton for Forbes. Beer production skyrocketed in the early years of the twentieth century, she writes. “By 1916, there were approximately 1,300 breweries in the country. But four years later, a nationwide ban on alcohol went into effect.”
One of the ban’s more intentional effects was that breweries went out of business. By the time Prohibition ended, later in 1933, only a handful of them were still around, she writes. Here’s how some breweries survived:
Milking the Dairy Industry
Several breweries used existing skills of keeping things (previously beer) cold and manufacturing large quantities of foodstuffs and turned to the dairy industry. As Nick Greene writes for Mental Floss, Anheuser-Busch and Yuengling both started making ice cream. Yuengling even already owned a bunch of refrigerated trucks. “Yuengling became the Yuengling Dairy Products Corporation and kept making ice cream until 1985,” he writes.  Other breweries did the same.
And during Prohibition it was possible to get PBR-brand cheese. “Aged in the brewery’s ice cellars, Pabst-ett cheese was sold to Kraft in 1933,” writes Vinton.
Brewing Soft (Or Not-So-Hard) Drinks
Breweries already knew how to make fizzy drinks (beer), so it’s unsurprising that many turned to beer-related products which didn’t fall under the category of “alcohol” as well as soft drinks. Outfits like Schell’s Brewing Company, Saranac Brewery and Pittsburgh Brewing Company all made "near-beer" and other soft drinks.
They also found a new beer-related product to sell. “Many breweries, including the manufacturers of Schlitz, Miller and Pabst, turned their attentions to malt extract,” writes Greene. Breweries sold it for use in baking and cooking as well as touting its health benefits.
“The real reason people bought it, however, was to use it in making their own beer, or ‘home brew,’” Greene writes. In the end, Prohibition agents caught on to this use, he writes, but “a court eventually ruled that the extract was legal, and people were able to make as much, um, bread as they wanted.”  
Brewing Dyes
Another natural fit for brewers was dyes, something the U.S. was suffering from a shortage of after World War I. Several breweries converted their equipment to domestically brew dyes that couldn’t be imported during the “dye famine,” Greene writes.
“Brewery owners weren’t the only people who noticed the similarity between alcohol and dye production; in a tasty reversal, many dye chemical plants converted to make illegal hooch,” he writes.
Prohibition didn’t keep people from drinking, but the idea that it failed to change drinking habits is false, according to recent work by historian Jack S. Blocker.
“Drinking habits underwent a drastic change during the Prohibition era,” he writes, with per-capita alcohol consumption not surpassing the pre-Prohibition peak until the 1970s.
According to Blocker, the cultural shift that enabled Repeal was the Great Depression of the 1930s, when Americans realized that temperance hadn't prevented a steep economic decline. Diversified business helped some breweries survive that, too.