Jakeorjacob

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Bought a refractometer a couple months ago and I'm really enjoying using it to measure pre-boil and OG before adding yeast. However, I was very confused to make a couple batches that I thought were under-attenuated because I kept using the refractometer to find the Brix (and then gravity) of the fermenting wort. I had no idea that the calculation for determining the gravity of fermenting wort is a) different and b) complicated.

So, my two questions:

1. What is the calculation?
2. What websites or apps do people use to find a reliable gravity using the Brix and OG of fermenting wort? I've seen a couple but am getting slightly different numbers from each one.

(I understand that I could just measure gravity using a hydrometer, but I am brewing one gallon batches (at least for a little while longer) and I hate to waste that much wort just to check the gravity. The refractometer works so much better and if I can find a reliable way to calculate, I will be a happy camper!)

Satisfaction

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Good timing, just went through this very topic in another post.

The website to use seems to be..

http://seanterrill.com/2012/01/06/refractometer-calculator/


Here is the post we were discussing the drawbacks of using a refractometer for calculating beer OG and FG.

http://www.homebrewtalk.com/f14/who-do-you-trust-hydrometer-refractometer-376738/index3.html

Jakeorjacob

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Sweet, thanks!

Sock

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Just drop the whole hydrometer into the batch instead of taking a sample. Make sure its really clean....!

Dan

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I had my refractometer doubts for awhile too, but after comparing a few batches' final gravity with a hydrometer and refractometer using a correction table I've found a refractometer pretty accurate. The two might not agree completely, like 0.003 off. I can live with that and have more beer in the end.

Satisfaction

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My same conclusion as well.. Had doubts, confirmed those doubts, and the significance of those differences are.. well insignificant in my opinion. Pick one and stick with it.

Jakeorjacob

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Nice. I like using the refractometer way better, and even if I was making ten gallons, the amount of liquid lost to a hydrometer would still irk me. It's like half a beer! I have no need to "sample" that much beer every time I check the gravity - the few extra drops left over from the refractometer is usually enough to get an idea on how the beer is doing.

Epimetheus

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Another post about refractometer accuracy for FG. I'm getting a refractometer anyway.
http://www.homebrewtalk.com/f11/refractometer-final-gravity-fermented-beer-333712/
... and from that thread
Sock, great idea to put the hydrometer in the wort bucket - if you can read it.

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Frige

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I have been just dropping mine into the wort bucket for a while now. Much easier. Refractometer is next on my goodie list.

Yooper

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I always use a refractometer for prefermentation readings for my beer and wine. Then, for the FG, I use a hydrometer.

I've never had my refractometer be accurate, even with corrections, with a finished beer or wine. Ever.

But I love my refractometer, and I use it several times on each brewday.

I use my hydrometer on the day I package the beer. It doesn't take much beer for a sample- I think it's 3 ounces. I just drink that sample. I can "afford" to give up three ounces of beer with a FG reading to ensure I don't get bottle bombs. It's worth it!

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