Sugars settling in hydrometer sample?

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Tidwellc

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Hey guys,

I've got a few batches under my belt with an eBIAB setup I bought and I've been trying to take a lot more samples throughout the process to find out what my efficiency is. My last batch was a while ago so I don't quite remember exactly the numbers I was getting, but basically: I'm taking samples pre-boil and post-boil (as well as pre-pitch), and the numbers I'm getting just don't seem to be adding up. After dumping into the fermenter and whipping the hell out of it to oxygenate, I'm hitting my target FG. However, my pre and post boil numbers seem extremely lower than they should be.
When I take either of those samples (from the faucet at the bottom of the vessel), it's too hot to measure, so I either let it stand or even throw in the fridge for a bit while I let it cool (and yes, I'm correcting for temp).
Are the sugars in the sample tube settling towards the bottom and throwing my readings off? Has anyone else experienced this?
 

kh54s10

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Probably not. I don't think the sugars will settle at all. More likely you are getting poor efficiency with you BIAB. Try crushing the grain finer.
 
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Tidwellc

Tidwellc

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Probably not. I don't think the sugars will settle at all. More likely you are getting poor efficiency with you BIAB. Try crushing the grain finer.
Yeah, I mean its dissolved in solution, so you wouldn't think it would. Maybe my efficiency is low, I just figured I'd be missing my FG target if it was.
 

RM-MN

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For about $20 you can get a temperature compensated dual scale refractometer that will allow you to take a hot sample and have an instant reading. The other plus of the refractometer is that it only takes a drop or 2 for a sample. Some will claim that the gravity scale isn't accurate and that you need to use the Brix scale and calculate but mine matches my hydrometer when I compare.

https://www.amazon.com/Refractomete...argid=aud-801738734305:pla-420967809789&psc=1
 

IslandLizard

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+1 to using a refractometer for quick gravity measurements while brewing.

Just keep an eye on potential evaporation of a very hot (near boiling) sample while transferring to the prism, as it may throw off your reading quite a bit (too high).

Inspect your grain crush, if too coarse, efficiency will be lower. Most BIAB grist can be milled very finely, much finer than the average LHBS/mail orders do.
 

Vale71

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Solids in solution don't settle, ever. We can also rule out stratification in the boil kettle since you do BIAB and presumably don't sparge.
All it leaves are temperature effect and evaporation in the sample during cooling.
Bi the way, a temperature compensated refractometer compensates for the effects of temperature on the refractometer, not for the temperature of the sample, so cooling is always required. The good news is that it will be such a tiny sample that it can be cooled in less than a minute.
 
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Tidwellc

Tidwellc

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For about $20 you can get a temperature compensated dual scale refractometer that will allow you to take a hot sample and have an instant reading. The other plus of the refractometer is that it only takes a drop or 2 for a sample. Some will claim that the gravity scale isn't accurate and that you need to use the Brix scale and calculate but mine matches my hydrometer when I compare.
I actually have one, I think that same one, that I never really trusted because of hearing stuff like that. It sounds like that's what I need to use. The sample should also cool down a lot faster.

+1 to using a refractometer for quick gravity measurements while brewing.

Just keep an eye on potential evaporation of a very hot (near boiling) sample while transferring to the prism, as it may throw off your reading quite a bit (too high).

Inspect your grain crush, if too coarse, efficiency will be lower. Most BIAB grist can be milled very finely, much finer than the average LHBS/mail orders do.
As far as boiling off, maybe it will help to grab a bigger sample and let it cool a few minutes? I'm thinking still pretty small but more than a few drops.

As far as my grain, I don't have a mill, but I am using a metal bucket with a false bottom without an actual bag. I'd be worried that milling too fine and it would pass through the holes. I have been using rice hulls with every batch and have had zero issues with draining.

Solids in solution don't settle, ever. We can also rule out stratification in the boil kettle since you do BIAB and presumably don't sparge.
All it leaves are temperature effect and evaporation in the sample during cooling.
Bi the way, a temperature compensated refractometer compensates for the effects of temperature on the refractometer, not for the temperature of the sample, so cooling is always required. The good news is that it will be such a tiny sample that it can be cooled in less than a minute.
I actually fly sparge. But it's sounding like I need to use my refractometer, taking smallish samples and letting them cool. Would I be screwing up by taking maybe a shot glass sized sample and sticking it in the freezer for a couple of minutes before reading?
 

Vale71

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I actually fly sparge. But it's sounding like I need to use my refractometer, taking smallish samples and letting them cool. Would I be screwing up by taking maybe a shot glass sized sample and sticking it in the freezer for a couple of minutes before reading?
Personally, I use a plastic pipette to take a small sample (no more than 2 milliliters) and then turn the pipette around so that all the liquid flows to the bulb. I then place the bulb under a stream of cold water and the sample is cooled in less than a minute while minimizing evaporation as much as possible.
 

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As far as boiling off, maybe it will help to grab a bigger sample and let it cool a few minutes? I'm thinking still pretty small but more than a few drops.
I scoop about 1/8 cup out and let it sit for a few minutes. I then transfer a few drops by dipping a butter knife into the cup.

Or use a sample pipette as @Vale71 described. I stick the bulb end in a glass with some ice/water for a short minute.
Now... I always seem to spray boiling wort all over the place when inverting the pipette after taking the sample from the kettle... :tank:
Anyone found a clever way around that?
 
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Tidwellc

Tidwellc

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Personally, I use a plastic pipette to take a small sample (no more than 2 milliliters) and then turn the pipette around so that all the liquid flows to the bulb. I then place the bulb under a stream of cold water and the sample is cooled in less than a minute while minimizing evaporation as much as possible.
That sounds like a really great way to do it! I'll try this!
 
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Tidwellc

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I've seen a lot of stuff out there about taking tons of measurements and using a spreadsheet to determine "wort correction factor" and that you shouldn't trust the reading at all until you do. Is this something I should do as well? Have you guys done this?
 

IslandLizard

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I've seen a lot of stuff out there about taking tons of measurements and using a spreadsheet to determine "wort correction factor" and that you shouldn't trust the reading at all until you do. Is this something I should do as well? Have you guys done this?
Nah. Most refractometer readings of wort are fine as is. As long as I'm within 3-5 points either side of the predicted/calculated, I'm not worried.

It's when I expect after the mash my first runnings to be to 1.045 and I get 1.025-1.035 I'd start looking for answers.

Now taking refractometer readings after fermentation has started, when there's alcohol present, where you do need to visit a calculator. I leave the WCF at 1.040, close enough, but you can tinker with that if you have accurate hydrometer readings to compare to.
 

kh54s10

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I just take the sample with a pipette. Drip it on the refractometer and read it. It actually starts a bit high, maybe .001 high, then stabilizes withing a few seconds. It is most often within .001 or .002 of the predicted OG. So I don't worry about any evaporation. If prediction is, say, 1.050 I don't care if the reading is 1.048 or 1.052. I don't really care if it is even a couple points farther off.
 

kh54s10

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It's when I expect after the mash my first runnings to be to 1.045 and I get 1.025-1.035 I'd start looking for answers.
First runnings at 1.045??? What do you brew 2% ABV beers. My OG is usually higher than that. First runnings are always right around 1.070. The sparge lowers it to pre-boil numbers. Big beers don't have as much sparge water and small beers have a lot of sparge water.
 

IslandLizard

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First runnings at 1.045??? What do you brew 2% ABV beers. My OG is usually higher than that. First runnings are always right around 1.070. The sparge lowers it to pre-boil numbers. Big beers don't have as much sparge water and small beers have a lot of sparge water.
That was a 2.7% Oat Mild mashed at 162F (!) for 30'. Targets were 1.028 preboil, 1.033 OG.
I ended up mashing longer and regained some.
 

dwhite60

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Even if you're doing brew in a bag you need to stir well before taking a gravity sample.

Just like pouring oil into water, the heavier fluid stays on the bottom. With BIAB the heavier, sugar laden, wort settles to the bottom of your pot. If you're on a RIMS system this might vary but even then I'd still give the wort a good stir. Cannot hurt anything.

Last beer I made I took my pre-boil gravity sample from the side of the pot and was about ten points under where I should have been. Took another sample from the middle of the pot and it was higher. Gave it a good stir and everything equalized, my last reading was spot-on.

All the Best,
D. White
 
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Miraculix

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Small hot break pieces can also throw off hydrometer readings significantly. An easy way to solve this is to let the sample stand for a few hours to let every matter drop to the bottom and take the reading afterwards only within the clear liquid. I tested this a few times myself, there were big differences between the settled and unsettled liquid, both having the same temperature, of course.
 
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