Author Topic: target an exact FG  (Read 756 times)

Offline redzim

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target an exact FG
« on: July 31, 2012, 01:26:36 PM »
OK I've been thinking about this for a couple days, while planning my next beer (a schwarzbier that I brewed this morning).

Say I'm trying to end up with 11gals of 1.048 wort in the fermenter... so I am dealing with 528 gravity points.... now 11gals of 50F wort is actually almost 11.5gals at 212F if you go with the 4% volume reduction, so at flameout, is my wort 1.046 (because 528/11.5 = 45.9) ???

And so my real question is, when designing a recipe, should I be targeting a final volume of 11.5 gal, or 11.0 gal?? because for a lowish-gravity beer, those 2 points make a difference.  But perhaps I'm over thinking this or missing something.

Obviously if I'm brewing a 1.065 IPA and it comes out at 1.062 or whatever, it's not such a big deal.

-red

Offline a10t2

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Re: target an exact FG
« Reply #1 on: July 31, 2012, 06:14:08 PM »
Target a final volume, after losses, that gives your desired volume into the fermenter. The wort contraction due to cooling will be constant, so it won't affect your process. If you lose, for example, 1.0 gal/hr, then you'd start with 13.0 gal before a 90 min boil to hit 11.0 gal post-chilling.

If you were to take a kettle gravity reading using hot wort, it would read ~4% low, but since there's no (practical) way to take a hot reading, it probably doesn't make sense to think of it that way. It's the gravity of the cooled wort that matters.
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Offline nateo

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Re: target an exact FG
« Reply #2 on: July 31, 2012, 07:50:58 PM »
Red - I'm the most obnoxiously pedantic person I know, and I don't stress about 2 gravity points.
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Offline weithman5

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Re: target an exact FG
« Reply #3 on: July 31, 2012, 08:01:18 PM »
red
if i understand your question is volume to target.  i brew to a target volume because i brew small batches and my buckets have little head room for more than 2g.  in fact i don't think i could adequately brew an ale in them.   but lets say you want your beer to be 1048 at 11gallons in the fermentor, than i would think you would be shooting for around 1050 at 11.5 flameout.  quite honestly, i don't think i would stress those few points.

by the way i hit the pilsner tonight. will send pm later

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Offline narvin

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Re: target an exact FG
« Reply #4 on: July 31, 2012, 08:27:54 PM »
You want 11gals of 1.048 wort, so... target 11gals of 1.048 wort  ;)

If you're measuring volume in the kettle during the boil, you'll have to adjust for the extra 4% expansion at 212.  Otherwise, for purposes of designing the recipe, measuring cold liquor, etc, you should be able to effectively ignore that.
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Offline redzim

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Re: target an exact FG
« Reply #5 on: August 01, 2012, 04:34:02 AM »
Thank guys for reassuring me... that's basically what I've been doing, targeting the final volume and gravity at 50-60F in the fermenter... but it's one of those things you suddenly start over-thinking and wondering if you're doing something wrong.

-red