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Old 02-10-2013, 03:58 PM   #1
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Default Hydrometer readings are unreliable?

It seems to me that all hydrometer readings, except for the final "true" gravity reading are unreliable. Since sweet wort is heavier than beer, your gravity readings will fluctuate depending on where in your fermenter you take your sample from. Take it from the bottom close to the trub and it will probably much higher than a sample drawn from the top. This could lead to people prematurely thinking they have hit final gravity. What do you all think?


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Old 02-10-2013, 04:14 PM   #2
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how early are these people taking readings? 2nd day in? when the beer is done, you'll get consistent readings days apart, no matter where you pull the sample. sometimes a yeast just ain't done rockin'. they just party a little slower.


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Old 02-10-2013, 04:17 PM   #3
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Quote:
Originally Posted by ryanhope View Post
It seems to me that all hydrometer readings, except for the final "true" gravity reading are unreliable. Since sweet wort is heavier than beer, your gravity readings will fluctuate depending on where in your fermenter you take your sample from. Take it from the bottom close to the trub and it will probably much higher than a sample drawn from the top. This could lead to people prematurely thinking they have hit final gravity. What do you all think?
Have you held a flashlight near a fermenting brew (assuming you have a clear carboy)? There is so much turbulence inside between falling debris and rising gas that the thing gets mixed pretty constantly. When the mixing slows, gas production is slowing, things are settling and you should be approaching final gravity at that point anyway.
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Old 02-10-2013, 04:28 PM   #4
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Thats an interesting idea. Im inclined to think the turbulence of fermentation keeps it mixed up pretty well. Really though, even if the interim readings are skewed by stratification what does it matter? The only measurements that matter are the OG and the FG.
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Old 02-10-2013, 04:33 PM   #5
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I have never had any of the issues for which you are questioning. That being said I only take certain readings:
1. Pre-boil
2. Post boil OG
3. Post fermentation FG (two readings at 2 days apart, generally not before the 10-14th day of fermentation)

IMO/IME there is no need to take any more frequent readings than this. In addition, I verify the calibration of my hydrometer at least once per month and all readings are temperature corrected.
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Old 02-10-2013, 10:15 PM   #6
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Is it possible to test specific gravity of wort or beer using the mass/volume method?

We mix ceramic glazes and then weigh a 500ml sample in grams. Since water weighs 1g/1ml the weight of the sample divided by the volume gives you a specific gravity ratio.

Any reason that wouldn't work for beer? Anyone want to weigh in on the level of accuracy vs a hydrometer?
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Old 02-10-2013, 10:27 PM   #7
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Um, are you talking about an extract top off batch or a full volume ag, pm or extract batch? The only time a grav reading is "unreliable" is if it's a top off batch. If you're doing a full volume boil, the the gravity is going to be the same all the way through the wort, since nothing is being mixed up.

If it is a top off extract batch, and you topped off to the correct final volume, as I say in this thread, you just go by what your recipe says it should be. It's foolproof. If it's AG or Pm, and you are topping off, if you took a pre- top off gravity reading, you can use a dillution calculator like the one in beersmith to estimate it. Actually even if you are doing an extract top off batch, if you were to dump the wort into your fermenter and it had graduated volume marks, you could take a gravity reading of the undiluted wort, the input that, with your current volume, along with the intended volume, and selecting "dilluting with water" and the dillution calculator would tell you what your gravity will be once it's topped off.

SO really, if you think about it there's really no point where a hydromter reading has to be unreliable.......And the other time, if you've topped off with water and didn't do what I just said you just need to go with the hydrometer reading of the original brewers of the recipe....so even then there's not instance where a hydrometer is unreliable.

You just kinda need to know HOW it is reliable in any given situation.
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Old 02-10-2013, 10:38 PM   #8
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In terms of final gravity, it's always reliable, because the alcohol content is going to be the same all the way through. By the time fermentation has occurred that cavitation by all the yeast has homogenized everything. location near the trub or whatever your theory is is going to be no different in terms of sugar being converted to alcohol. It's only when the density of the extract and the water used to top off is different will the potential for any issues as mentioned by me above be in play.

People have been using hydrometers to ascertain final gravity since the 4th century, and honestly noone's ever had a false positive in terms of when a beer is complete...you take two readings over a few days and if they are the same, the beer is done, that's, that.
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Old 02-10-2013, 10:41 PM   #9
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Quote:
Originally Posted by duboman View Post
I have never had any of the issues for which you are questioning. That being said I only take certain readings:
1. Pre-boil
2. Post boil OG
3. Post fermentation FG (two readings at 2 days apart, generally not before the 10-14th day of fermentation)

IMO/IME there is no need to take any more frequent readings than this. In addition, I verify the calibration of my hydrometer at least once per month and all readings are temperature corrected.
This is pretty much my story, only I usually don't mess with anything until at least day 14, unless I'm trying to rush a recipe.

I'm curious though, unless your are confused on weather or not fermentation is done, why would you take regular readings?
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Old 02-10-2013, 10:43 PM   #10
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It is possible to slice a hair in half length wise, but why would you want to? My point? Hydrometers, used properly are more than accurate enough for thousands of brewers. If you want to reinvent the wheel or rent an electron microscope knock yourself out. But it won't make your beer any better...


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