Dear Mr. Wizard,
I have recently tried a few different recipes using Beano (as described in BYO a few years back) and Splenda to flavor. I have made three batches in the last 8 months. I make a batch as normal, once even split a Blue Moon clone in half (half to bottle as “normal” ale and the other half to receive Beano and continue to ferment). I wait until primary fermentation stops and then add a couple crushed tablets of Beano. In a few days, the airlock starts bubbling again (maybe once every 5 minutes) and it will bubble for a couple weeks (it does slow down). Then I take a hydrometer reading, and usually end up pretty low, around 1.006. I then add about 2 cups of Splenda to give the beer a little body and no added carbs. Then, I mix a priming sugar solution, boil and bottle the product. In a week or two I try one of the brews and get a very high foaming beer . . . one that needs a huge glass to pour into, and then come back in ten minutes or so when the foam sinks back into liquid. Literally, when you pour, you get about an inch of liquid and the rest foam. The beer itself has a little off taste, but not horrible. I attribute the flavor to the Splenda.
Charleston, South Carolina
The Wizard replies:
I often ask myself what I started with an article that was intended as a science humor piece. The problem with Beano Bräu is that it actually works and you can definitely make bone dry beer with this over the counter digestive aid. Then, Chris Colby fueled the flame by balancing the dryness of Beano beers with Splenda. If you think that an off-flavor is associated with Splenda, you should quit using the stuff and determine if it is the cause of the off-flavor.
I must admit that these beers are true Frankenbräus! The cause of your foaming brews is easy to explain. Beano contains the enzyme amyloglucosidase (AMG) and this enzyme breaks down unfermentable dextrins into fermentable sugars. Since enzymes continue to do their thing as long as substrate is present, any residual dextrins in the beer at the time of bottling will slowly be converted to fermentable sugars in the bottle and yeast will then convert the sugar into alcohol and carbon dioxide.
Although you may think the Beano activity is complete when you bottle, it is probably not. The rate of enzymatic activity depends on the concentration of enzyme and substrate and sometimes is inhibited by the concentration of the product. In practical terms this means that the effects of Beano are really obvious at first then become difficult to monitor because the reaction rate dramatically tails off as dextrin concentration falls. So you think the beer is as dry as it is going to get and end up bottling early.
This is a real concern for brewers who make light beers by adding AMG to the fermenter. If you are a large commercial brewery the obvious solution is to pasteurize the beer and denature the AMG. While homebrew can be pasteurized, you would have to bottle carbonated beer. Obviously you do not want to pasteurize before the beer has carbonated because dead yeast equals flat beer. I am not advocating pasteurizing homebrew and consider this solution as a really bad home method.
Another way to use Beano is to add it to the mash or wort prior to boiling. This will take some experimentation to allow enough time for the AMG to do its thing to the dextrins. Since enzyme activity is accelerated by heat, you will find by trial and error how many tablets are required to affect wort fermentability without extending your brew day. The AMG used in breweries is produced by the mold Aspergillus niger and is stable at high temperatures, usually up to around 176 ºF (80 ºC). This means you can dissolve the Beano in your mash water prior to mashing or in the wort collected prior to boiling. The boiling step will denature the AMG along with the native malt enzymes and your gas problems should go away. I always thought Beano was supposed to prevent gas, not cause it!