Refractometer reading pre-boil question....

[jbaysurfer]

So I usually use a refractometer for my preboil and OG readings, then switch to a hydrometer for my post fermentation readings.

Yesterday I was brewing a blonde with an expected OG of 1.048 at 70% efficiency. Which I hit dead on.

I batch sparge, and while the final runnings were being pumped to my boil kettle, I was also heating the wort, and it was getting close to a boil. I stirred it well, took a coffee cup and scooped a few ounces out of the boil kettle for me preboil measurment, then let it cool to room temp while I continued heating the wort. When I came back after it had cooled completely (probably about 70F in my garage) and took my refractometer reading and I got a 1.054 reading. Looked at beersmith and realize I had just defied physics and taken more then 100% of the available sugar out my grain!

I checked the refractometer calibration with some distilled water and did another reading...same thing.

Later on, as I mentioned, the refractometer worked just as I'd expected and my OG reading was spot on.

Any ideas how I got such an errant reading? Does it have something to do with the fact the wort I sampled (even though cooled before reading) was getting near boil/hot break?

 

[dgez]

I'm not a refractometer expert, I just ordered one yesterday. The only reason I'm making a comment is because i read through a few forums regarding refractometers. There is something called a brix correction factor. You can use beersmiths refractometer tool (under tools/refractometer) to help. Not sure if this is why the readings are off or not...

 

[gr8shandini]

. . . while the final runnings were being pumped to my boil kettle . . .

I think what happened is the same as the extract posts where the wort and the top off water aren't properly mixed. I had the same thing happen once and now only test for pre-boil gravity once all of the runnings are in the kettle and I stir the hell out of them.

 

[Bensiff]

My money is on cheap refractometer...I bought mine on ebay, while it looks and feels sturdy, it sometimes gives errant readings so I always double check. Mine has ATC, I notice that when I put a few drops on it, it will initially be a few points lower than after letting it sit for a minute. If I let it sit for five minutes it seems to sometimes really jump up into a range that is not possible. Perhaps its a little evaporation, IDK. I think it is one of the best tools a brewer can have and as such I am thinking of upgrading to a high quality one that I can really trust.

 

[Bensiff]

I think what happened is the same as the extract posts where the wort and the top off water aren't properly mixed. I had the same thing happen once and now only test for pre-boil gravity once all of the runnings are in the kettle and I stir the hell out of them.

Yup, a good point. Now here is my question, that might impact thoughts on the matter (if not sorry for hijacking)...I notice that my initial reading at the beginning of the boil doesn't match the ending boil reading. Say I get a reading that converts to 1.038 with 8 gallons and I plan to boil to 6 gallons so that should mean my grav at the end of boil should be 1.050; however, when I get to the end of the boil my gravity is always higher say 1.054. That shouldn't be possible.

 

[jbaysurfer]

Yup, a good point. Now here is my question, that might impact thoughts on the matter (if not sorry for hijacking)...I notice that my initial reading at the beginning of the boil doesn't match the ending boil reading. Say I get a reading that converts to 1.038 with 8 gallons and I plan to boil to 6 gallons so that should mean my grav at the end of boil should be 1.050; however, when I get to the end of the boil my gravity is always higher say 1.054. That shouldn't be possible.

I wouldn't think (well, this is my first blush reaction, see below for more thoughts) it would be a lack of mixing of the first runnings and the final runnings. Theoretically, not even the richest, most sugar dense first runnings can give you a reading of over 100% extraction. So even if I hadn't thoroughly stirred the boil kettle contents prior to taking my sample, I shouldn't have gotten a reading this high.

It IS a cheap refractometer. But this was the first problem of this nature I've seen.

One other thought about the mixture suggestion: I wonder if a hot break is a hyper concentration of sugars rising to the top of the kettle so that even though I mixed it thoroughly, the fact it was still on the verge of hotbreak meant the sample I took with my coffee cup (just stirred it up well, then took a cupful off the top) WAS indeed hyper concentrated?

For your issue, I'd have to guess that you either A) Had more wort to start with then you realized, or B) Boiled off more then you realized. Even a quart difference will impact the final reading. So if you're a pint high on your mash runnings, and a pint low on your fermenter volume, you'd get a higher reading then you expected.

 

[gr8shandini]

What is the volume that Beersmith is calculating the extraction percentage on? Almost by definition, your first runnings have to be over OG, so I could see how it might think you went over 100% if it's extrapolating your gravity reading over the full pre-boil volume.

 

[Bensiff]

I wouldn't think (well, this is my first blush reaction, see below for more thoughts) it would be a lack of mixing of the first runnings and the final runnings. Theoretically, not even the richest, most sugar dense first runnings can give you a reading of over 100% extraction. So even if I hadn't thoroughly stirred the boil kettle contents prior to taking my sample, I shouldn't have gotten a reading this high.

Your first runnings are going to be really high gravity, probably in the 1.070-80's. So, if you took your reading before finishing sparging the gravity would seem abnormally high.

One other thought about the mixture suggestion: I wonder if a hot break is a hyper concentration of sugars rising to the top of the kettle so that even though I mixed it thoroughly, the fact it was still on the verge of hotbreak meant the sample I took with my coffee cup (just stirred it up well, then took a cupful off the top) WAS indeed hyper concentrated?

Hot break is protein material coagulating, not sugars. However, foreign materials or bubbles can cause misreads as can having some dried wort on the cover plate...which would amount to concentrated sugar; however, I do not know what impact that would have on light refraction since its dried and not liquid.

For your issue, I'd have to guess that you either A) Had more wort to start with then you realized, or B) Boiled off more then you realized. Even a quart difference will impact the final reading. So if you're a pint high on your mash runnings, and a pint low on your fermenter volume, you'd get a higher reading then you expected.

That's the problem, I have a sight glass on my brewkettles and am confident they are marked accurately so the disconnect between the pre and post boil remains something of a mystery to me. I am a little suspicious that when I buy a better refractometer that issue may disappear though.

 

[gr8shandini]

Yup, a good point. Now here is my question, that might impact thoughts on the matter (if not sorry for hijacking)...I notice that my initial reading at the beginning of the boil doesn't match the ending boil reading. Say I get a reading that converts to 1.038 with 8 gallons and I plan to boil to 6 gallons so that should mean my grav at the end of boil should be 1.050; however, when I get to the end of the boil my gravity is always higher say 1.054. That shouldn't be possible.

Oh yeah. I had that problem, too. Drove me nuts for about a year until I figured it out.

Turns out that water expands by about 5% between room temperature and boiling. And, of course, most of us calibrate their sightglass / story stick at room temp. However, the expansion is not linear and most of it happens to occur between 150 and 212F. So even though you hit all the marks in terms of volume when you're lautering, you end up "losing" about 4% if you boil right down to where you want to be.

That doesn't sound like much, but it ends up being about a quart for a 5.5 gallon batch, which is enough to throw your OG off by a few points.

 

[jbaysurfer]

What is the volume that Beersmith is calculating the extraction percentage on? Almost by definition, your first runnings have to be over OG, so I could see how it might think you went over 100% if it's extrapolating your gravity reading over the full pre-boil volume.

Your first runnings are going to be really high gravity, probably in the 1.070-80's. So, if you took your reading before finishing sparging the gravity would seem abnormally high.


Hot break is protein material coagulating, not sugars. However, foreign materials or bubbles can cause misreads as can having some dried wort on the cover plate...which would amount to concentrated sugar; however, I do not know what impact that would have on light refraction since its dried and not liquid.



That's the problem, I have a sight glass on my brewkettles and am confident they are marked accurately so the disconnect between the pre and post boil remains something of a mystery to me. I am a little suspicious that when I buy a better refractometer that issue may disappear though.

111.6% on Edit: 7.15G

So yeah...that's what has me scratching my head. But now I realize that the first runnings gravity COULD indicate higher then 100% extraction if they weren't properly mixed. I guess I'll just chalk it up to that, but to be honest, I'm unsure how much more I could've stirred it up. I basically had about a pint left to pump in from the last runnings, so I had 7G when I mixed and measured it. Anyway, thanks for the feedback to everyone!

For your issue, the post just above makes a great point about water expansion while heated, which, in my boil kettle is an issue I've thought about, but in the mash cycle, I can honestly say that I'd never considered it.

 

[rico567]

I bought one of the $25 eBay refractometers. It was dead on zero with RO water after i took it out of the box, and it's performed well since. On the few occasions where I got a reading that didn't make any sense, I immediately cleaned the refractometer and drew another sample- and it was a good reading. I have no idea as to the cause of these strange readings, only that they happened, and the best course may be to just do another sample.

 

[jbaysurfer]

I bought one of the $25 eBay refractometers. It was dead on zero with RO water after i took it out of the box, and it's performed well since. On the few occasions where I got a reading that didn't make any sense, I immediately cleaned the refractometer and drew another sample- and it was a good reading. I have no idea as to the cause of these strange readings, only that they happened, and the best course may be to just do another sample.

Yeah, I'm happy with mine. After talking myself in a circle, I've come back to realize that a first running heavy sample COULD produce the reading I got. I could'nt retake the sample after that because I was already boiling. It was just a preboil read, and the postboil OG came out perfect. All good.

I love my cheap refractometer. I still use a hydrometer post ferm, but the refractometer is faster and only takes a couple drops post mash and post boil.