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Hydrometer to "determine" fermentation completion

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Maybe I can receive consensus on my question concerning the use of a hydrometer to test when fermentation is complete. I've read various opinions on this site and I'm hoping to clarify 1 question. I'm fairly new at home brewing and have just been using Mr. Beer's recipes using the HME and the LME additive.


In a scenario of using only a hydrometer to judge when the fermentation is complete, I am unclear about what alcohol % measurement should indicate completion. Per Mr. Beer's guideline, they give a range of alcohol % to expect. That range is fairly broad. Can I expect to be more precise? For example, I'm about finished the fermentation (16 days) of an American Ale and the alcohol reading I get calculates to 3.7% which is in the range Mr. Beer lists for the %. But it could go up to say 4.5% or so.


From reading various posts, the main opinions that I recall are 1) don't worry about it; ferment for 3 weeks and bottle, and 2) take multiple measurements and when you receive the same calculations, the fermentation process is complete.


Any other ideas or confirmation of the 2 opinions stated above?


Thanks all. Your posts accelerate the learning curve of new guys.


 


 

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To determine when fermentation is complete is not a measurement of Alcohol, it is a measurement of Gravity.  When you first put a batch into the LBK you should take and record the Original Gravity.  After 21 days you take another sample of the beer and check the final gravity,  over a period of 3 days if the FG ( final gravity) is the same for 3 days then fermentation is complete and it is time to bottle.

To determine ABV (alcohol by volume you subtract the FG from the OG and muttliply by 131.  As per Mr.Beer instructions.

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Thank you. I confess, I mixed up my semantics which you corrected and also provided a clear answer. 

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There was a great video of how to use a hydrometer posted a while back. Perhaps a search could dig it up. Secondly, after 2-3 consistent readings your beer is most likely done. I normally leave it the full three weeks anyway, partly because I'm lazy, partly to let the yeast "clean up" as some brewers recommend. There are some who say not to leave the beer sitting once fully fermented, and this has merit as well. Surprisingly, I've had a couple of brews not finished after 3 weeks, and needed an extra few days, and that is when my hydrometer was really useful. Good tool in helping to learn the art of brewing. BTW, even the same recipe, using the same yeast and temperature may vary each time you brew it. Science, art, craft, alchemy, magic - somehow we make beer. Yumm.

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Right.  You're testing for a steady Final Gravity, not ABV.  FG will be about 25% of OG.  

What I do is take my OG reading and calculate my expected FG.  If OG is 1.040, than I expect 1.010 for FG.  At around 18 or 19 days I take my initial FG reading.  If it's around 1.010, I cold crash (I cold crash to get the trub to solidify and get more beer into bottles).  If it's above by more than a little I take another reading 24 - 48 hours later.  Only once have I had to gently stir the beer to get things going and it dropped a tad lower.  It should be noted that some beers, like Stouts, tend to finish pretty high, around the 1.020 mark, I had that happen several times.

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Again, thanks all for the advice. I took a reading today (end of day 17) and the FG read 1.008, best my eyes could read. About the same as 2 days ago. Fermentation temperature was 73/74  degrees. I'll leave the keg alone for a few more days and either bottle the beer or try a cold crash in a refrigerator for a day. The flat beer tastes good now but I see some flecks of yeast (white specks?) floating on the beer.

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I wouldn't worry about the little yeast rafts floating on top. when you bottle just be careful not to get the bottom trub sucked up in the bottle. hop or yeast floaties wont hurt anything. trub on the other hand might make off tastes.  I did a kit called caribou slobber from another company. after 21 days I had bright orange yeast rafts floating on top... bottled it and it was fine. cant recall what yeast I was using.

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Just about 25%; OG was 1.04 as I recall since I'm at work.

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Zorak, how was the caribou slobber? I always drool a little when I look at my Northern Brewer catalog. 

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Target FG would have been 1.010, so you're below that and good.  Bottle away!

I've brewed three batches of "Caribou Slobber" - well a combination of that tweaked with Adventures recipe.  Excellent.

7.4 lbs LME

1 lb Crystal 80

.25 lbs Pale Chocolate

.125 lbs Roasted Barley

.5 lbs Flaked Oats

.5 lbs Carafoam

1 oz each of Kent Goldings (60), LIberty (25) and Wilamette (15).  Danstar Windsor yeast.  

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if I recall.. if you like English nut brown ales you'll like this. its a little coffee.. a little toffee.. a little  malty.. I used s04 I think and wasn't particularly careful about temps ( a little high) so I got a little fruity too. it wasn't bad, it just wasn't my 'thing'.

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It is nice to use a hydrometer to check the apv, but I have concern with the lbk,  it is so small I really do not want to pull off enough wort to fill a vessel for the hydrometer and throw it out, and it is not deep enough to put it right in. Also I worry about putting the wort back in after from a sanitation perspective, so I do not use one. I just go by what I put in, ferment until finished activity, and check the taste (not sweet) before bottling. So far so good :-). And I really do not care closer than +/-0.5%. Also I worry about getting wort on outside of keg tap allowing organisms to grow on it  (not cleanable) - potentially infecting the beer when bottling. If I was doing 5 gals, no concern, I would chuck it after measuring.


How do you folks do it?

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Consider getting a refractometer.  Mine was $28 on Amazon, and may be the best $28 I ever spent.  I treat an OG reading as my brew goes into the LBK, and a FG reading before bottling as the official readings, but use the refractometer to monitor the fermentation.  It only needs a very small sample, so it does not use a lot of wort or create risks of infection. 

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Note that the alcohol content affects the refractometer reading, but software like BrewCalc on my iPhone handles the conversion to gravity readings.  The refractometer with this correction comes pretty close to the official hydrometer readings. 

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Nickfixit said:

It is nice to use a hydrometer to check the apv, but I have concern with the lbk,  it is so small I really do not want to pull off enough wort to fill a vessel for the hydrometer and throw it out, and it is not deep enough to put it right in. Also I worry about putting the wort back in after from a sanitation perspective, so I do not use one. I just go by what I put in, ferment until finished activity, and check the taste (not sweet) before bottling. So far so good :-). And I really do not care closer than +/-0.5%. Also I worry about getting wort on outside of keg tap allowing organisms to grow on it  (not cleanable) - potentially infecting the beer when bottling. If I was doing 5 gals, no concern, I would chuck it after measuring.

How do you folks do it?

I sanitize the hydrometer and tube, take the OG  reading, and dump it back in.  You can spray up into the spout, or fill a shot glass with sanitizer after taking the sample.

For FG I drink the sample.

Chucking samples is against the law. ..

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