Ongoing refractometer oddity

I got a refractometer when I transitioned to all grain brewing, so I could make sure I was hitting my numbers post-mash but it seems to be giving me wildly inaccurate readings... but only for wort!!. The first time I tried it during an all-grain batch, it told me I was off by 15 points, which put me at an efficiency of like 50%. In a panic, I added a calculated amount of DME... only to find the refractomer reading was still off.

Another time, I brewed an extract-only batch that contained a known quantity of extract and water, but the refractomer again was off by 10-15 points. I confirmed the discrepancy with my hydrometer after letting the wort sample cool to room temperature.

No here's what's really puzzling: I just made a 30 Brix sample of 35g of distilled water and 15g of table sugar, and the refractometer was dead on. So it seems like the problem only shows up when I measure wort.

Is there something special I need to be doing?

Temperature. Samples must be near room temp to get a good reading

My refractometer only reads the Brix scale.
I multiply the Brix reading by 4 to get gravity.
This will not work if there is alcohol (post fermentation) present.
I never had to calibrate mine.
You made a sample of 30 Brix wort? That's roughly a gravity of 1.120

runningweird said:

Temperature. Samples must be near room temp to get a good reading

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If you are only using a couple drops, the temp. doesn't matter as it drops to room temp. right away.

Many of the refractometers which show SG are not correct. Use the brix scale and convert. Also I would calibrate a few times a year with distilled water, and do this where you brew. I noticed mine drifts a bit if I am inside or outside., different color of light or something is my guess.

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Alright guys, thanks for the all the advice. Unfortunately I have to retract my original statement that my refractometer doesn't work well with wort. I did an all-grain batch this weekend and the pre-boil gravity once again came out ridiculously low on my refractometer. But I also cross checked a sample with my hydrometer (after it cooled), and came up with the same number. I did these checks a couple more times and each time the refractor and hydrometer were in near perfect agreement.

So… I guess that means I have to accept the fact that I’m getting ~55% efficiency in my mashes rather than blame my refractometer

The trouble is that I’m not really sure how to improve my mash efficiency. I don’t have a lot of all-grain batches under my belt, but I started off with good efficiency numbers then all of a sudden my efficiency starting taking a dive. The dive coincided with my purchase of a refractometer hence my confusion

Batch #1: Partial Mash, mash efficiency 76%
Batch #2: Partial Mash, mash efficiency 80%
Batch #3: All-grain, mash efficiency 70%
Batch #4: All-grain, mash efficiency 75%
Batch #5: All-grain, mash efficiency 80%
—— purchased refractometer ——
Batch #6: All-grain, mash efficiency 60%
Batch #7: All-grain, mash efficiency 50%
Batch #8: All-grain, mash efficiency 57%

All of the batches were BIAB except the last, in which I did a batch sparge with a 52-qt cooler that I just built. I’m tempted to blame the grain crush, but I’m not sure what to look for to know if the crush is good. Any ideas?

I had a similar issue and found that mine was a salinity refractometer, not sugar.

So many beers... so little time.

Were you getting your grains crushed from the same mill, or different mills?
I mill my own, bought a barley crusher. I use the factory setting, which I think is .045. So far so good.
Do you stir well when mashing in?
How many times did you sparge your grains, do you stir like hell before you drain your runnings?

Since you are brewing BIAB, your crush should be very fine. I do mine on a Corona style mill like this one (http://www.amazon.com/dp/B000U5NZ4I/?tag=skimlinks_replacement-20) and have it set until the plates grind when it is empty. The grain comes out looking a bit like corn meal but it gives me about 80% efficiency no sparge. Most places that mill grain for you do not mill it fine enough for good efficiency. It's a compromise between acceptable efficiency and stuck sparges and stuck sparges do not make for happy customers so they mill it a bit coarse and sell a bit more grain to make up for the loss of efficiency.

runkelia said:

Were you getting your grains crushed from the same mill, or different mills?
I mill my own, bought a barley crusher. I use the factory setting, which I think is .045. So far so good.
Do you stir well when mashing in?
How many times did you sparge your grains, do you stir like hell before you drain your runnings?

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Different mills, different homebrew shops: some online and some from my LHBS. My LHBS has two different hand cranked mills, one of which has given me good results and one that has given me bad results on two occasions.

I do try to stir the mash well at the beginning, then leave it alone for the rest of the mash. Also, with the BIAB batches, I typically squeeze the crap out of the bag, then sparge in 170F water for ~30 minutes, and squeeze it again. With my single batch sparge attempt, I went for equal volumes of 2 runnings. I stirred both each time before draining.

RM-MN said:

Since you are brewing BIAB, your crush should be very fine. I do mine on a Corona style mill like this one (http://www.amazon.com/dp/B000U5NZ4I/?tag=skimlinks_replacement-20) and have it set until the plates grind when it is empty. The grain comes out looking a bit like corn meal but it gives me about 80% efficiency no sparge. Most places that mill grain for you do not mill it fine enough for good efficiency. It's a compromise between acceptable efficiency and stuck sparges and stuck sparges do not make for happy customers so they mill it a bit coarse and sell a bit more grain to make up for the loss of efficiency.

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I'm transitioning away from BIAB and moving to batch sparging in a cooler, but I don't think the crush was ever very fine. I can definitely see how a shop would tend to error on the side of coarse crush.

I really think a mill should be next on my purchase list though... I always feel like I'm taking a gamble when I rely on the settings of the brew shop; it looks like I got lucky the first few times and now I've hit a streak of bad luck. Besides, with my own mill I can buy grain in bulk.

When starting out aim for consistent rather than high. Once you hit the same efficiency every time you can try to increase efficiency and actually be confident your change caused the increase. I also am if the opinion that anything between 50 and 85% is OK for homebrew. If it is consistent you can adjust your recipe to make up for it, and you are talking about only a few dollars of grain. The big guys get hurt because it could be a few $1000 in grain... but that is a different beast.

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Take a handful of your milled grain. There should not be any whole kernels left. The milled grains should have an overall coarse texture, mostly irregularly shaped granules around 1/16" diameter with a finer sand-like powder and then some flour mixed in. There could be a few bigger pieces in it, but not too many. The husks should be mostly intact, ideally, not shredded too much. You can do a search here or Google for images.

Do you have a model # or reference to the refractometer you are using? I don't think my refractometer could measure 30brix, or if it could it would be at the very top of its range. It might be you are using a refractometer that is not meant to be used with the typical gravities of wort?

Bsquared said:

Do you have a model # or reference to the refractometer you are using? I don't think my refractometer could measure 30brix, or if it could it would be at the very top of its range. It might be you are using a refractometer that is not meant to be used with the typical gravities of wort?

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I believe it is an RSG-100ATC, an eBay special I got a couple years ago for not much money. I think it shipped directly from China. It goes up to 32 Brix max. I made the 30 Brix test solution using 35g of distilled water and 15g of table sugar (i.e. a 30% by weight sugar solution). It measured the solution exactly at 30 Brix, and I've subsequently learned that the wort measurements were right after all. I might have had some problems with it one point last using it outside in the hot weather, but I now I keep it inside during my brews and always check the calibration with distilled water.

Anyway, I've concluded that my mash efficiency just sucks, and the low readings I'm getting are not the fault of the refractometer.