Bloody Refractometer!

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OK. So I don't trust my refractometer any more.

My OG was 14.5o, which was about right (~1059 SG).. didn't check with my hydrometer. So let it fly.
My reading yesterday was 6.25o (1024) at 19C, and today it was 7.5o (1030) at 19C. :huh:

So I used my hydrometer today because I didn't believe it was at 1030 after 5 days. Anyway, Hydrometer reading was 1012.

Something is very wrong. If I look at water, it reads 0. That's fine. If the gravity is high, it seems fine..
SRM 7. Golden maybe slightly coppery in colour. Is that it?

I calibrated it to 0 with water. I think that's right.

Can anyone offer any advice? (other than chucking it out).
You have to Beersmith tools refractometer conversion and put fermenting wort as what you are measuring. Fermenting wort gives weird readings until you convert it. There is also a conversion table somewhere on the forum do a search for it.
I presume you know the calc once fermenting, so was the refrac completly dry when taking both readings after ferment started?

You're remembering to correct for alcohol?
I get some funny readings from my refrac sometimes too. The gravity might be up a couple of points from what it was a few days ago, then a few days later it's even lower, despite calibrating the instrument each time with room temp RO water. I think it has something to do with the light more than anything else. Overcast days sometimes result in a fuzzy, difficult to read line, sometimes in a surprisingly sharp one, and the halogen downlights in the kitchen always give a fuzzy reading on it.
great link. Thanks Fourstar :)

Keiran: i just put in your readings and it does come out close your FG (1.011)
Make few tests. Then tell me how to think :p

OG is usually just right. FG usually differs a lot.


I measure my wort with brix meter. I get 10.0 bx. That is approx. 1.040 SG.
So, I let the ferment hapen and measure second time. I get 4,5 bx. Then that onebeer calculator tells me that FG is ~1.004. So I'm happy to bottle?
Well, I want to be a sure. So I use areometer and get 1.012 why? Because net is full of incorrectly calculated scales that based same formulas I guess.

If I put same values to Beer Engine, I can get same values than my areo / hydrometer gives me.
(Ofcourse you must give calibrate values first, but I have digital brix meter and it's calibration factor is 1.)

That was my point. You must know your equipments and limitations, right?


Quite good apparent attenuation peoples have here.
59 - 11 = 48 / 59 ~ 81%

And now I shut my mouth on this issue... ;)
Is it normal for it to go from 14.5 down to 6.25 and then back up to 7.5??
Noope, unless you're reading at different temps or excess trub or something in your sample.

Or there were a few drops of water still in the pipette... i've found I have to be REALLY careful with what's in the pipette - I usually suck, shake, squirt 2 or 3 times each time before actually testing - 1 or 2 drops of water could easily end up being 10-20% of the sample on the refracto....

Also: temperature correction plays a big part in screwing up readings. With such a tiny sample, it doesn't seem to matter what the fermenting temperature is - if the refractometer is sitting in a 30degree room, the couple of drops of 19degree sample will pretty quickly get to 30. I keep a cup of water next to the refractometer (on top of my fermenting freezer), and usually recalibrate it each time I use it... then the sample in the pipette is swished around in the cup of calibration water for 30 seconds... if i'm really careful, the reading will agree with the hydrometer...
I humbly thank you all for your enlightenment!

The fog has lifted, and it all makes sense now. :)
I shall hold my refractometer near and dear.
We all do it at some stage... for me the freak out period was only about an hour or so before the head-slap realisation about the fermenting wort correction. :rolleyes:
Noope, unless you're reading at different temps or excess trub or something in your sample.

For me I'm thinking it was flocculated yeast in the sample. I need some kind of wine-thief type thingy.

How do you other chaps extract your samples? Do you pull some out the tap, let the crud settle for a while (to let suspended yeast/trub drop out), and temperature equilabrate at the same time, before measuring?

My pipette was pretty clean, but I think now I have a much better appreciation for the necessary approach to get a reliable reading.

I suspect the 6.25>7.5 was due to water (from pipette)/yeast (from fermenter) [either, or both] in the sample on FG-1 day.
I just put my finger in the sample then wipe the refractometer screen. And make sure everything is dry beforehand.
I have some small (about 2ml) plastic (disposable) pipettes they work fine since you only need a drop or two.
I think the question was more related to how you're getting your sample from the fermenter - opening the top/removing gladwrap and taking from there, or pouring a sample from the tap and taking it from there
I just put my finger in the sample then wipe the refractometer screen. And make sure everything is dry beforehand.
That-lightly dip fingertip in the sample Or a few drops off a toothpick or something, only liquid drops onto the refractometer that way.

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