specific gravity question

coastwx · 12-11-2009, 05:18 PM

First of all, thanks to everyone for the great information in all these forums. I've been lurking for the last month or so, and have absorbed a lot from the experienced brewers as well as the newbies. I'm the type that jumps straight into the deep end when trying something new. Since I had an unused 5 gal water cooler my first batch was an all grain Boulder Beer Co Mojo IPA clone. I immediately followed that up with an American Ale and then a Fat Tire clone. After reading many posts here about sanatizing I became worried that my use of beer bright with well water rinse may have led to an infection of my first three batches. Although these brews are still conditioning in bottles, I've chilled samples of all and I'm stoked that two actually taste great (Mojo and Fat Tire) and the one is definitely drinkable! BeerSmith is a great tool!

On to my question. My main mistake from the first batches is the lack of robust before and after gravity measurements. I did a Stone IPA clone last weekend and did my gravity measurements this time. Post boil, pre-pitch gravity was around 1.072. The fermentation was vigorous to the extent that I blew the air lock off the carboy even though I used fermcap, so I've learned the hard way to use a blow off tube. Anyway primary fermentation has take place for 6 days now and the gravity reading yesterday (as I was cleaning up the beer splatter off the closet walls) was all the way down to 1.015. I was surprised the gravity was so low given the 15 lb of grain used and just 6 days after fermentation. Does this sound like a reasonable drop if density? Thanks in advance!

FYI, It seems I read somewhere that lower mash temp can lead to higher conversion to alcohol. My mash was suppose to be at 148 deg, it was at the start, but at the end it was a little lower around 144 deg.

**android** · 12-11-2009, 05:21 PM

what kind of yeast did you use? I wouldn't be all that surprised if it finished in 6 days. most of my beers are done within or at one week. yes, a lower mash temp definitely contributes to a more fermentable wort, so that would make sense... as long as you pitch the right amount of yeast, aerate your wort properly and allow good fermentation temps, yeast will do the bulk of primary fermentation pretty quick IMHO. and of course letting it sit on the yeast cake for another week is a solid idea.

**david_42** · 12-11-2009, 05:41 PM

You've got 80% apparent attenuation, which is in keeping with your low mash temperature. This will reduce the malt flavors and body, but that's not too big a deal in an IPA.

coastwx · 12-12-2009, 07:20 PM

I thank you both. It was Nottingham yeast.

Just took another reading today and it was down to 1.012