Adjusting Volume to Hit SG

Thanks to my apartment dwelling, I'm a partial-mash, partial-boil guy. My process is typical: I boil, say, three gallons and then add sterilized water in the fermenter to get up to five. After that I check my starting gravity and pitch.

The other day I came up with an idea: what if I measured the gravity and volume of the wort before I added the water? Then, I would be able to calculate how much water I would need to add to hit my starting gravity exactly.

The result would be that I would always, guaranteed, hit my starting gravity on the spot. Instead, my volume would vary.

Is this good thinking?
Does anyone else do this?
Would it really make much of a difference in the finished product?

Thanks!
Matt

Good thinking - sure.

Anyone else do it - probably.

difference - more repeatable/predictable results. I for one never really care about a variance in the SG. It is what it is, and I don't think I've ever brewed something and later said, "dang, if only I wasn't off on the SG by 5 pts!"

I'd rather have an extra 6 pack of slightly weaker ABV beer than hit my OG perfectly. Just my .02

hlumbard said:

I'd rather have an extra 6 pack of slightly weaker ABV beer than hit my OG perfectly. Just my .02

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But, what if it turned out you could get an extra 6 pack of target ABV beer than overshoot your OG?

If you have a refractometer, it would be very easy to do this. I always take a refractometer reading of my boiling wort, many times actually. But I have become a gravity nut since I got my refractometer. Heck, I take readings of my orange juice.

Version 1.2 of brewtarget has a tool that performs the exact calculation you want. It will be out next week or soon. Check my signature.

chug187,

I'm full AG but I use your method in a sense. I always plan to boil down until I'm about a quart below my target volume. Then I pour everything through a strainer bag and into my fermenter. Then I check the gravity. Based on my reading, I add a small amount of water to hit target OG. There are a couple reasons I do this:

1) When I strain, there's a lot of wort left in the hops. If I top up to target volume, I'll always be under target OG.
2) When I add the top-off water, I pour through the hop trub in hopes of picking up a couple extra points.

Here's something that I think a lot of people don't consider when topping off: so you build a recipe to a specific OG and specific IBU. If we experienced no loss of wort due to absorption by the trub, we'd hit our numbers perfectly. But since that's not the case, I think a lot of people have to make the decision of target OG or target volume.

Personally I think target OG is more accurate, because if you hit your volume but have low OG, that means not only is your beer more dilute in gravity, but also in IBUs. The same way that our post-boil trub absorbs sugar/gravity points, it also absorbs isomerized alpha acids.

So remember, if you top off to target volume knowing that you'll have a lower gravity reading than expected, you also can't claim your beer has the same number of IBUs. Everything will be pretty close to target, but not exact. I'm too much of a perfectionist for everything not to be exact.