Suppose you took a sample today and found gravity to be exactly the predicted FG, or within a point or two. If that sample was saved - just kept in the gravity tube - would there be any validity to measuring it again the following day to ensure that it hasn't changed?
Measuring gravity...twice from same sample?
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Falstaff
A Bad Influence
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You would have to cover it, or evaporation would make the gravity appear to go up. You would also have to cover it loosely enough so it wouldn't blow the top off if it continued to ferment.
Temp differences and less pressure from less liquid on the yeast could change things too, though someone else with more technical experience might have more to say about this.
Temp differences and less pressure from less liquid on the yeast could change things too, though someone else with more technical experience might have more to say about this.
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I don't know. Your sample is a pretty idealized version of what's in your fermenter. It is no longer in the same environment. Not the same trub and yeast on the bottom or stuff that was on top.
And there is probably something to be said for the scale and such were some processes might not be able to happen in a smaller sample than a larger volume and vice versa.
I'd drink it or toss it. But perhaps if you are interested in finding out, do both and see what happens on several batches.
And there is probably something to be said for the scale and such were some processes might not be able to happen in a smaller sample than a larger volume and vice versa.
I'd drink it or toss it. But perhaps if you are interested in finding out, do both and see what happens on several batches.
I almost hate to admit it but I have wondered the same thing (LOL). Maybe some day on a batch I'll do it. I have a refractometer now so the sample size wouldn't suck the carboy dry taking a butt load of samples. I can't believe some one hasn't tried this before though, lot's of scientist types here not to have had, maybe a little embarrassed to admit they did. 
Cheers,
Joel B.
Cheers,
Joel B.
If you're bottle conditioning, I definitely wouldn't trust this method without knowing for sure it's reliable. (Bottle bombs)
Oh no, I wouldn't either, that's for sure. It would be interesting to see the results though.
I'm sure there's all kinds of scientific reasons why or why not this is viable. I'm waiting for some of the fermentation experts to chime in and lead us on this path. Maybe we are just a bunch of silly thinkers and dreamers, drinking too many or our gravity samples.(LOL)
I hope they do, I would love to hear the reasoning, one way or the other.
Cheers,
Joel B.
jerrylotto
Well-Known Member
Something I recently realized is that you want to measure FG on flat beer. If there are carbon dioxide bubbles nucleating on your hydrometer, you are not going to get an accurate reading - not to mention having to visualize the meniscus through foam. Shaking or passing through a coffee filter can help to degas beer to prepare it for an accurate measurement.
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