Since we're also doing not-small businesses, here's from an earlier follow-up of mine on how Anheuser-Busch survived through and prospered after Prohibition:

Oh, yeah, the beer companies--especially A-B--were absolutely furious about Prohibition passing the state legislatures. And why not? They had their financial data; they knew people were buying the stuff. They felt financially but also heard the public outcry when beer was temporarily banned during World War I so the ingredients could go to the war effort. August Busch, who was by that point running the company with the help of two adult sons, decided with them to fight it out rather than simply go quietly into the night (they were just stupidly wealthy and could have, but it seems to have been a mixture of greater ambition, loyalty to the family legacy, and loyalty to the company's almost 7000 employees).

So in addition to finding ways to keep doing business, like the lucrative ginger ale market, they focused their efforts on Prohibition actually being against the will of the people. (Which, of course, the popularity of bootlegging would suggest--and, in fact, those in-home bootleggers were pretty much getting their supplies from A-B). They took out newspaper ads, distributed leaflets, and wrote letters to the occupant of the Presidency. August in particular hunted down every ounce of hypocrisy on the government's part (continuing to allow alcohol sales on cruise ships) and would not let them rest about any of it. And--most famously and effectively--as the Great Depression took hold, he launched a massive publicity campaign to the effect that the revival of the brewing industry would employ thousands and thousands of Americans and help pull the country back to fiscal health.

The end of Prohibition is actually the saddest part of the story. Of course initially sales did very well, but it turned out that people didn't really want Budweiser anymore. They liked their watered-down, sweetened, mixed-drink style alcohol they had gotten used to during Prohibition. August B. utterly refused to even consider changing the formula. Watching his beloved business child, the family legacy, fade away at the same time his health completely cratered, in 1934 he shot himself. More than ten thousand people paid their respects at the casket viewing.

The second August (August Jr. or Gussie), one of his sons, had weathered Prohibition in the nearly pointless job of attempting to operate a brewery that couldn't brew real beer. He had the vision of his father and grandfather, but also the vigor. As president of the newly formed Brewing Industry, Inc., he oversaw the revival not just of A-B and Budweiser but of beer in America, period, now that the industry had to deal with new requirements of middlemen (no more proprietary taverns) and increased taxes. One technical innovation that A-B pioneered was the use of beer cans, although I believe bottles were still more popular. But far more important was publicity.

Those of you familiar with Budweiser's frequent modern day ad strategy of selling sentiment rather than beer in its TV spots will recognize its roots with Gussie's 1930s marketing push. A-B/Budweiser was only secondary--the tagline following messages of patriotism, American strength, the importance of hard work, the perseverance of immigrants who braved the ocean and worked their way up from the bottom. I swear I am not making this up; it's straight from Knoedelseder:

"Confidence sailed our forefathers across the turbulent Atlantic," said another [ad]. Confidence helped our grandfathers extend the stubborn frontier, and made ours the strongest and most abundant land on earth today. Confidence is ready now to take America further still.”

The only mention of Budweiser came in the ads’ tagline: “Live life, every golden minute of it…Drink Budweiser, every golden drop of it.”

Very few, and they were the exception. While there were 31 operating American breweries by June 1933, 331 in operation by the end of the year, and 766 in operation by 1935, Prohibition had the effect of clearing the decks for large manufacturers, who used their market advantages to prevent the return of hundreds (if not thousands) of local and state breweries. The Brewers Association has an excellent chart of the historical count of American breweries over the past 145 years.

Large manufacturers were better able (not all did) to stay in operation during Prohibition, producing "near beer." Anheuser-Busch manufactured Bevo; Pabst made Pablo; Schlitz made Famo; Miller made Vevo, and so on. As /u/sunagainstgold points out, A-B and other brewers also diversified their product lines, selling raw materials and other items.

What's important to note is that Prohibition came at a time when the American beer industry was already consolidating rapidly. In 1873, the earliest year for which I've seen reliable statistics, there were 4,131 breweries in the United States. It's possible that there were more before that date, but inaccurate and spotty recordkeeping makes it difficult to track. I'd be interested in reading a good study that discusses that period in American brewing.

Market consolidation was already well under way by the time of Prohibition, thanks to rationing during World War I and improved technology that allowed beer to be transported long distances (and maintain high quality). In addition, the widespread of light lager-style beers allowed uniform mass-production on a large scale. By 1919, there were only 669 breweries in the United States.

The post-Prohibition rebound was short-lived; after 1935, the number of breweries resumed the decline that had been in place since the first years of the 20th century. That trend did not reverse itself until the first years of the 1980s, thanks in part to a 1978 law passed by Congress that allowed homebrewers to make small amounts of beer tax-free. That fact encouraged homebrewing, giving the first draft of craft brewers the skills needed to start their own businesses. Further, the development of the local, home-grown movement during the 1960s and 1970s (the Whole Earth Catalogue was a symptom of this) created a ready market for those early counterculture craft breweries, allowing them to reverse the trend of the 19th and early 20th centuries.

As of June 30, there are 6,655, the most in American history.

Since we've already got a couple of answers about beer, let's talk about wine. Unlike breweries, the preponderance of American wineries operated using a Bordeaux-like "grower" model wherein winemakers were also expert viticulturists with sizable tracts of fertile land, and thus, still had grapes to keep them afloat. This isn't to say the wine industry wasn't decimated: Vitus Vinifera (the grape species from which nearly all wine is made) don't produce particularly good table grapes, and other more common table grape species (such as Vitus Labrusca) don't make particularly good wine... and if you have a difficult time picturing someone swishing fine Cabernet in a Speakeasy, it's because it didn't happen very often.

Wine did, however, still get made. Ironically, religion proved to be a boon to the flagging wine industry. Communions and Passover Seders still utilized wine (and, generally speaking, didn't care much about the quality). Likewise, Vinifera grapes were still grown. As a result of a loophole in the Volstead Act (which allowed for the production of "nonintoxicating" beverages, yet failed to adequately define that term), many wineries were bold enough as to market compressed bricks of grape concentrate, upon which one might find the following label:

WARNING: Do not place this brick in a one gallon crock, add sugar and water, cover, and let stand for seven days or else an illegal alcoholic beverage will result.

About 80% of California's wine industry went tits-up during prohibition. A lot of raisins and shitty Manischewitz-style Kosher wine got made. The number of wineries didn't reach it's robust, pre-prohibition levels until the early 90's (although it's more than tripled since then). Vinification, wherever it is practiced in the world, is a craft deeply rooted in familial tradition, and the only thing that was more deeply wounded than winemaking tradition was the American demand for fine wine. The biggest blow to the American wine industry was the fact that more than a decade of an entire nation drinking back-alley hooch ruined our collective palates and dampened the demand for fine, hand-crafted wine.

Enter the Mondavi family.

The Mondavis, like many in the wine industry, were fruit-packers during Prohibition. In 1943, they came into ownership of the Charles Krug winery - the former estate and namesake of the godfather California's wine industry. Peter Mondavi made the wine, and his brother Robert ran the business. Over the course of the next two decades, the brothers built a tidy little business in a niche market. In 1965, Peter told Robert to go fuck himself, and Robert Mondavi found himself a fifty-something wine professional out on his ass. He secured a few hundred acres of prime real estate in Napa Valley and started a eponymous winery. The mid sixties were when the California wine industry finally blew up - Both branches of the Mondavi family, and many other world-class winemakers (such as Schramsberg's Jack Davies) began to produce wine that could make the best French Domaines and Chateaus blush. Meanwhile, wineries like Gallo and Sutter Home started to mass-market affordable table wines. The latter introduced a sweet, arrested fermentation, light rose they dubbed "White Zinfandel" that has been gracing Big Gulp cups en masse since the early 70's.

Grapes endured. Fine winemaking tradition did not. As most of us are aware, California produces some of the finest wines in the world today. So too do gallon jugs of table wine grace the bottom shelves of Wal-Marts the world over. Quality and quantity are both in abundant supply in the California wine industry, but it took some time to get there.

(Much of this is paraphrased from Karen MacNeil's "The Wine Bible" and Madeline Puckette's "Wine Folly")