Yeast's Influence on SG

BlackHat · 10-07-2008, 12:19 AM

While writing the recipe for a batch of stout, I predicted the SG to be about 1.075. I got this number by working off of (4.1 on FAQ 1-4 Answers @ Williams Brewing) which didn't have an estimate for the pound of lactose I added to the brew. Come brew day, as soon as I was tucking the carboy into the closet I realized I hadn't taken an SG reading. I know SG should be taken before pitching the yeast, but I was curious what to expect out of this beer. So I sanitized a wine thief and took a sample. The reading came out to 1.098!

Was my approach of predicting SG by such rough means the reason my prediction was off or was it the fact that I hadn't calculated lactose and yeast?

eschatz · 10-07-2008, 12:27 AM

Well, 1 lbs of Lactose would have bumped your SG up about 6 points from 1.075. I have never made a milk/sweet stout so I have no idea how much to use. However, you can do the math. Wort does settle in weird ways though. If you don't have a thoroughly mixed wort your sample will not read correctly. It's not good to mix the beer up or slosh it around when it's fermenting so I think your sample was off. I wouldn't worry about it. Is this an extract batch? If you got a good boiling going the whole time and used the right amount of water with an extract batch your SG will pretty much be spot on.

BlackHat · 10-07-2008, 03:58 AM

Yeah it was an extract recipe. 9# of LME, about 2# of specialty grains, and 1# of lactose. Definitely designed to be a sweet stout. I planned on this being a big beer, but not *that* big. So I'm going to say you're right on the misread. Thanks