Inaccurate OG...any other way to calc %alcohol?

In the mayhem of making my first batch on Sunday the OG reading had to be taken quickly and because of froth I couldnt take an accurte reading.....i was more concerned with the rest of the process. Is there another technique I can use to calculate % alcohol once its finished?

Thanks.

Was it an AG or an extract batch??

If it was an extract it should be really easy to establish your OG.

It was extract. OK, so how? I mean retrospectively?

White Labs has a kit, but it'll cost you.

http://www.whitelabs.com/lab/alcoholtestkit.html

Exactly! Thats what I thought....not so easy retrospectively Thanks

You need a refractometer.

ayupbrewing said:

Exactly! Thats what I thought....not so easy retrospectively Thanks

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Extract will have a specific and known gravity. If a known amount of that extract is dissolved in a known amount of water, the OG can be calculated very precisely, without any need to measure it.

When brewing all-grain, or simply just not knowing how much water and extract were used (which would be incredibly sloppy), there is another method. It requires taking a FLAT sample of the finished beer, and measuring the OG using a hydrometer AND the (uncorrected) OG using a refractometer, and then doing a bit of math.

People who use a refractometer frequently find the unknown variable of the *corrected* FG, by calculating it using two known variables - the OG and uncorrected FG. That equation can be rearranged to figure out a different unknown variable, the OG, if the two other variables are known... in this case, both the corrected and uncorrected FG (the hydrometer and the refractometer measurements, respectively).

Similarly, one could also rearrange the equation to determine the uncorrected FG if both the OG and corrected FG are known, but as you can probably tell, there's no real point to doing so.

ayupbrewing said:

It was extract. OK, so how? I mean retrospectively?

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Let us know the weights/volumes of extract and any sugar, or any other fermentables, you used plus the exact volume of wort that went into your fermenter and we should be able to work out your Original Gravity.

Or, alternatively, you could input the details into a recipe calculator, such as beer calculus, and get the result.

So i actually got the recipe from hopville/beer calculus and see that the OG should be 1.068, but it gives a range presuamable because things might not always go perfectly etc. SO i was just wondering how close to 1.068 I was since i missed it.
Thanks though.

Emjay: Thanks.So im pretty good with equations but your description left me a little confused. If i take a gravity of a finished beer is that not FG rather than OG as you said - if i read your post correctly, I have a refractometer at work so I could do this calc if I could follow it better. Thanks

Ayup!

If I'm not mistaken, I think the range shown might be the parameters acceptable for the beer to still fall under the appropriate BJCP category.

ayupbrewing said:

Emjay: Thanks.So im pretty good with equations but your description left me a little confused. If i take a gravity of a finished beer is that not FG rather than OG as you said - if i read your post correctly, I have a refractometer at work so I could do this calc if I could follow it better. Thanks

Ayup!

Click to expand...

Yep, I mentioned figuring out the FG by using the OG and uncorrected FG because that's the equation that is most commonly used (to find the correct OG with a refractometer).

But this is the relevant part of my post:

"That equation can be rearranged to figure out a different unknown variable, the OG, if the two other variables are known... in this case, both the corrected and uncorrected FG (the hydrometer and the refractometer measurements, respectively)."