Refractometer Discrepancies

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NobleNewt

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So, I usually use my refractometer to monitor fermentation especially when things get closer to FG. I don't use it exclusively to make bottling decisions, but I use it to get a feel for where the FG is before I pull a hydro sample. Since I re-started brewing a few years ago, I've basically used a version of a "Big Mouth Bubbler" from my LHBS. I put a spigot on the bottom, and when I take refrac. readings, I pull a minuscule amount of beer (about an ounce) to test my refrac. gravity.

I've noticed, if I take samples a few days apart, my refrac. readings may actually increase by .5-or-so Brix. If I take a second sample immediately after the first, my second reading will be more in line with what I expect to see. My hypothesis is that one of a couple of things is happening:

1) There's residual beer inside of my spigot that is evaporating slightly and when I pull a new sample, it has a higher sugar concentration. When I pull the second sample, the spigot is effectively "flushed out."

2) There's somehow a stagnant layer of sugars near the spigot or I'm pulling off some more concentrated wort. I don't think this is quite as possible, but not sure.... I've noticed that if I give my fermenter a gentle swirl, the gravity readings are closer to what I expect to see as well.

Has anyone else noticed anything like this? Not a big deal, I'm just wondering how I can take more consistent readings.
 

k-os

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Your sample that you take a couple days after the previous may still be fermenting, and creating more alcohol. This could cause your reading to increase due to the refractive index of alcohol.

Try spraying sanitizer up into your (closed) spigot after you take your first sample, and then take another sample a few days later.
 

slurms

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may still be fermenting, and creating more alcohol
That will definitely throw off a standalone Brix to SG reading, but I doubt it the more alcohol will cause an increase of brix/SG. To get the true story, you've got to convert your final brix reading to your FG, which takes into account your OG (and I guess the alcohol). I got a function to convert original/final brix readings into FG here. Refractometer Calculator « SeanTerrill.com
 

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slurms

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Ignore the attached figure. That's a plot of FG vs. final brix using that equation (wasn't supposed to stay attached....)
 

slurms

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Aaand just read the rest of your post... If you are truly worried about that, you can just drain a half an ounce (or more than the few drops you've been doing) just to start pulling from the bulk of the beer to get a more uniform sugar/alcohol distribution for your measurements. Sure it's more wasted beer, but it's a whole lot less than a for a hydrometer.
 

sounddoc

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I recently went back to the hydrometer for post fermentation readings, and with some patience (just wait a week) I'm usually only taking one sample. But this isn't the droid you're looking for, so...

I can't answer your question specifically, but I can offer my experience; more alcohol = higher brix readings, relatively. You absolutely need to convert your refract. readings to gravity, i.e. read only the brix number, not the gravity number. Once fermentation has started, the gravity reading will always be effected by the alcohol content. I usually use beersmith to convert the readings, but I'm sure there are other calculators out there online. Also, if I let a sample sit for a few minutes, it'll actually change. I notice this with post mash readings. Maybe it's temperature related, but they get higher if I let it sit for a minute. Evaporation maybe? Eh... It's not space rocket fuel.

One last thing: is your refractometer calibrated? Do you have some distilled water handy? Since you only need a few drops you could do a science on the stove and capture stream from boiling water. You don't need much, and the kids are enthralled for a few minutes.

Good luck!
 

slurms

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Also, if I let a sample sit for a few minutes, it'll actually change.
I definitely have tried to use that to my advantage when I'm convincing myself I'm close to my expected OG. I think I've heard the reading will be skewed lower with warmer temps, but I'm not certain on that...
 

sounddoc

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I'm starting to think refractometers are useful for starting and original gravities. After that, it's really just a way to impress your friends and convince your wife that your hobby is actually a legitimate one.
 

slurms

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Nothing screams "this is real science" than looking through a refractometer. Hydrometers just don't cut it. I always tell my girlfriend I'm trying one of the homebrews for "science". Works every time...
 
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NobleNewt

NobleNewt

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I recently went back to the hydrometer for post fermentation readings, and with some patience (just wait a week) I'm usually only taking one sample. But this isn't the droid you're looking for, so...

I can't answer your question specifically, but I can offer my experience; more alcohol = higher brix readings, relatively. You absolutely need to convert your refract. readings to gravity, i.e. read only the brix number, not the gravity number. Once fermentation has started, the gravity reading will always be effected by the alcohol content. I usually use beersmith to convert the readings, but I'm sure there are other calculators out there online. Also, if I let a sample sit for a few minutes, it'll actually change. I notice this with post mash readings. Maybe it's temperature related, but they get higher if I let it sit for a minute. Evaporation maybe? Eh... It's not space rocket fuel.

One last thing: is your refractometer calibrated? Do you have some distilled water handy? Since you only need a few drops you could do a science on the stove and capture stream from boiling water. You don't need much, and the kids are enthralled for a few minutes.

Good luck!
I guess it would help if I knew how refractometers worked. I mean, I know the general idea, but when alcohol gets into the equation, I guess I don't really understand. I always use Northern Brewer's refractometer adjustment tool. When I plug in my Brix OG (11.5) and my current Brix (6), it tells me that my OG is 1.046 (which it was on my hydro) and the current brix (~6.2), I get an adjusted SG reading of 1.011...

Now, if I plug, say, 6.0 brix in, it drops the SG estimate to 1.010... Which means more alcohol, but a lower gravity reading. I guess I'm confused by what you're saying that more alcohol means higher brix.. Sorry if that's more confusing than it needs to be.

And, to answer your question, it's been a while since I've calibrated, but it's been consistently wrong for that whole time, I assume! 🙃
 

k-os

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I guess it would help if I knew how refractometers worked. I mean, I know the general idea, but when alcohol gets into the equation, I guess I don't really understand. I always use Northern Brewer's refractometer adjustment tool. When I plug in my Brix OG (11.5) and my current Brix (6), it tells me that my OG is 1.046 (which it was on my hydro) and the current brix (~6.2), I get an adjusted SG reading of 1.011...

Now, if I plug, say, 6.0 brix in, it drops the SG estimate to 1.010... Which means more alcohol, but a lower gravity reading. I guess I'm confused by what you're saying that more alcohol means higher brix.. Sorry if that's more confusing than it needs to be.

And, to answer your question, it's been a while since I've calibrated, but it's been consistently wrong for that whole time, I assume! 🙃
Refractometers measure the sugar density by equating how light refracts (bends) as it goes through the liquid to a scale (Brix).
When there is alcohol present in your sample it changes how that light gets refracted because it has a different refractive index than a sugar solution. It causes the light to be bend differently, and typically indicates a higher gravity on the Brix scale.
 
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NobleNewt

NobleNewt

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Refractometers measure the sugar density by equating how light refracts (bends) as it goes through the liquid to a scale (Brix).
When there is alcohol present in your sample it changes how that light gets refracted because it has a different refractive index than a sugar solution. It causes the light to be bend differently, and typically indicates a higher gravity on the Brix scale.
Thanks! Makes sense.
 

sounddoc

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More alcohol = higher brix relatively. For theoretical purposes, if you pull a sample that reads 6 and add some alcohol to it (immediate not through fermentation) it'll read higher than 6. So during your fermentation your gravity comes down, your refractometer's brix reading will too, just not as fast, hence the correction needed. Sounds like you get it, I'm probably just making things more confusing!

For your original question, yeah, let the bung run for a few seconds then sample. Or just wait!! ;)
 
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NobleNewt

NobleNewt

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More alcohol = higher brix relatively. For theoretical purposes, if you pull a sample that reads 6 and add some alcohol to it (immediate not through fermentation) it'll read higher than 6. So during your fermentation your gravity comes down, your refractometer's brix reading will too, just not as fast, hence the correction needed. Sounds like you get it, I'm probably just making things more confusing!

For your original question, yeah, let the bung run for a few seconds then sample. Or just wait!! ;)
No that's a good explanation and what I thought you might have been saying before!

FYI, I pulled a hydrometer reading, and I was at something like 1.012, took a refrac. reading and still said something like 6.5. Not sure that's worth anyone's time or effort, but there it is!
 

sounddoc

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That means your refractometer's calibrated and your beer is most likely done fermenting. I plugged your numbers into Brewer's friend and it all looked good to me. Cheers!

Now does it taste like bandaids? If so welcome to the club.
 

slurms

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Now does it taste like bandaids? If so welcome to the club.
I've been trying to track down what I think is that flavor. No clue where it comes from. Only happened in my one gallon brews. Bigger batches seems to be okay. I'm thinking it's from tap water with starsan perhaps. And not having fermentation temp control with those didn't help.
 

day_trippr

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There is no chlorine in Star San, but there can certainly be chlorine or chloramine in tap water thst can cause that band-aide character. Campden tabs will fix that cheaply...

Cheers!
 
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NobleNewt

NobleNewt

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That means your refractometer's calibrated and your beer is most likely done fermenting. I plugged your numbers into Brewer's friend and it all looked good to me. Cheers!

Now does it taste like bandaids? If so welcome to the club.
😂😂 No! It doesn’t taste like bandaids.. Tastes like dry Irish stout ready for some bottles!
 
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NobleNewt

NobleNewt

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There is no chlorine in Star San, but there can certainly be chlorine or chloramine in tap water thst can cause that band-aide character. Campden tabs will fix that cheaply...

Cheers!
Yep! I usually use 5 gallons of RO water and 2 gallons of tap water for most of my brews. I always break up a campden tablet in my strike water.

You can also boil your brewing water the night before. That has the added effect of precipitating out a lot of minerals as it cools down to room temp and boiling off the chloramine. Done that before and made good beer!
 
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