What would you do differently if trying to brew a low-carb beer? Could it be done with an extract brew?
Without an additive to dry the beer, it will be about 45-55 percent carbs. It's obviously possible to brew a light beer by starting with an OG in the 1.030's, but to get it low carb, I would suggest adding a pound of honey or another 100% fermentable sugar. That will give the yeast a second wind, and it will pull the FG down to around half what it was before the addition.
With this method, all-grain and extract will yield the same results.
1Some sort of enzyme to lower residual sugars is still a good idea, even with this approach. Dec 19, 2010 at 16:31
Beano is alpha galactosidase, which I've never put in my beer. And never will. HBS's often sell amylase, for restarting a stuck fermentation when other options fail. I suppose either could be used, but the only way to stop the action of these enzymes is to denature them with heat or chemicals, so I would worry that these would destroy flavor and mouthfeel, leaving a dry, barely-drinkable beer. Then again, most light beers are exactly that...– BrandonDec 20, 2010 at 1:25
1As you said, most low carb beers are exactly that and use some form of those additives. Don't let your own prejudices get in the way. You or I may not like beers like that, but that's how you make them. Dec 20, 2010 at 17:18
to clarify do you mean to add the pound of honey on brew day (i.e. at the end of the boil), or do you mean add it to the fermenter several days later when the yeast activity seems to die down?– G__Jan 13, 2011 at 0:46
yes, i should've been more clear. add the honey after fermentation finishes.– BrandonJan 17, 2011 at 2:24
It would be more difficult with extract than with AG, but it could be done. In a nutshell, you brew a low OG beer (maybe in the 30s) then use amylase enzyme or something like Beano to get it to ferment out as much as possible to a very low FG, which will reduce residual sugars.
With extract you have no control over the mash temperature of the wort so there could be a lot of unfermentable sugar's in there. I would say an amylase enzyme would be the best way to get it low enough.