I also checked the Anheuser-Busch website and, when I found nothing pertinent there, I did some Google searching. Among other things, I discovered that A-B sold five-pound packages of brewer's yeast under the Budweiser name during Prohibition. That was enough to allow users to make a large batch of beer. To see if A-B still had a yeast connection, I called their number from their website and spoke with a customer service rep and also a fellow in their materials section to whom I was referred. From these individuals, I learned that A-B sold its yeast business in 1988. The company that purchased the business resold it and then went out of business. I was told that Fleischmann's ended up with the business. But when I called Fleischmann's, I was told that they did not end up with the A-H yeast business.
From what I can tell, there are active and inactive forms of brewer's yeast. The active form can be used to make beer and has some limited baking applications. We know the latter from the work that Marc (widespreadpizza) and one or two other members conducted using beer yeasts. The inactive form is used as a nutritional supplement, and is typically found in vitamin shops. One can only speculate which form, if any, Pizzeria Regina is using. They may also be using normal commercial yeast. I was told by the A-B materials specialist that A-B now uses only liquid forms of yeast.
Through my research today, I also came across an interesting discussion of the Budweiser yeast finding its way into the hands of home brewers, at http://www.bayoubro.com/index_files/Excerpt2.htm.
The pertinent section is excerpted below:
UtAs to the theories of the availability of Bud yeast, the prevailing speculation is that it had long ago fallen into the hands of homebrewers, who traded it around under the moniker “Amateur Brewer’s Yeast”—or “AB Yeast,” for short, the AB being a wink and a nudge that really meant Anheuser-Busch. It’s a matter of historical fact that Anheuser-Busch was in the baker’s yeast business until 1988; one of the Yeast People told me that for a while the baker’s yeast strain it sold was actually the same as its Bud beer-yeast strain. True or not, AB Yeast ended up in the yeast labs where it is sold under guises such as the one that Steve Moore described.
Beyond that, there are other ways the Bud yeast could have made its way into this quasi-public domain. Bud is pasteurized and filtered before bottling to kill any existing organisms, including yeast, so there’s little chance that yeast could have been cloned directly from the beer itself. But given the tons of yeast that Anheuser-Busch uses annually and the number of people with access to it over the decades, it’s hardly unimaginable that a thimbleful walked out of a brewery someplace one day and into the test tube of a yeast rustler. And, as we’ll see, the possibilities don’t end there. The official Anheuser-Busch position is that the yeast it uses today is from the original strain acquired by Adolphus Busch in 1876 and is indeed proprietary. The company had no comment on whether people have or haven’t cloned it.
EDIT (5/1/14): For the Wayback Machine replacement for the bayoubro.com link, see https://web.archive.org/web/20080913182451/http://www.bayoubro.com/index_files/Excerpt2.htm