Ever have a refractometer read differently after sitting for a few minutes?

[slayer021175666]

Yesterday while brewing, I spooned out a little bit of my preboil wort and set the spoon on the counter to cool. I know it got clear down to room temp which was about 71 at the time and when I put it in the refractometer, it said 1.068. That was unexpected. I thought that it should be about 1.061. Anyway, I picked it up about 15 or 20 minutes later to look at it again and, it read 1.062. Anybody got any idea what's going on there?
Thanks

 

[Kickass]

This is the reason I stopped using my refractometer. Maybe mine isn’t high enough quality, I don’t know.

 

[DBhomebrew]

Probably the temp is still stabilizing. If left sitting long enough, quite possibly evaporation.

 

[slayer021175666]

Probably the temp is still stabilizing. If left sitting long enough, quite possibly evaporation.

Maybe, somehow I'm wrong but, it seems if it evaporated that would be water going away and it would make the brix count even higher. I'm pretty sure it was cooled down. It was just a little puddle in the bottom of a tablespoon. I don't know though. Thanks for trying to answer my question.

 

[slayer021175666]

This is the reason I stopped using my refractometer. Maybe mine isn’t high enough quality, I don’t know.

Maybe mine isn't either. It's the same ones you can buy in the little blue case on amazon. It always measure zero when I check it with distilled water, though. Hell, I don't know.

 

[DBhomebrew]

Maybe mine isn't either. It's the same ones you can buy in the little blue case on amazon. It always measure zero when I check it with distilled water, though. Hell, I don't know.

Mine, too.

 

[PberBob]

I’ve gotten odd readings if the glass and cover aren’t dry before I put the sample on it.

 

[tracer bullet]

OK so - A refractometer meausres the refraction of light (vs. a hydrometer that measures density / bouyancy). A refractometer works well IF you give it a good sample.

Collect your wort or whatever it is you want to measure. LET IT SIT a few minutes for the particulates in it to settle out some. Now take your measurement and be sure there aren't any bubbles in it.

Once I started giving it a little time to settle, my refractometer #'s got much more consistent and in fact were basically identical to the hydrometer measurements. If measured right away, they are always off.

So - let it sit a bit!

 

[slayer021175666]

OK so - A refractometer meausres the refraction of light (vs. a hydrometer that measures density / bouyancy). A refractometer works well IF you give it a good sample.

Collect your wort or whatever it is you want to measure. LET IT SIT a few minutes for the particulates in it to settle out some. Now take your measurement and be sure there aren't any bubbles in it.

Once I started giving it a little time to settle, my refractometer #'s got much more consistent and in fact were basically identical to the hydrometer measurements. If measured right away, they are always off.

So - let it sit a bit!

Okay. I thought I HAD let it set a little bit but, I'm thinking about it and maybe, the actual metal of the spoon kept it rather warm. I will try letting it sit longer. I did notice that when, I picked up the spoon again after doing what I thought was letting it cool, I could see more particulate in it. It didn't look as thoroughly mixed, anymore.

 

[slayer021175666]

I must say, original sample that I put in the refractometer after letting it cool in the spoon was just sitting there in the refractometer for another 10 or 15 minutes. It still gave me a way different reading than when I had originally looked at it. I hope I'm being clear. I'm just trying to say that the refractometer had the same sample in it when I picked it up the second time, as it did when I had left it from looking at it the first time. I'm still confused, I guess.

 

[slayer021175666]

Wait. Is it that it probably cooled down more in the refractometer? I can't see how much would evaporate when it was totally closed. Maybe the edges would evaporate a little bit but not, the liquid in the middle.

 

[dmtaylor]

I wish I knew why this happens, but yes, it happens, a lot. I always figured it had something to do with temperature or evaporation, maybe one or the other, maybe both. But I haven't nailed it down yet. Well heck..... even if I just measure at room temperature more than once, the value changes. I just think refractometers are a little less precise than hydrometers. I love my refractometer but I do recommend always measuring 2 or 3 times, then take the average reading, because it doesn't always come out the same. An average seems to me to be the best way to know where the real value probably is.

Keep in mind also, whatever you are using to get your sample, a spoon or dropper or whatever, should be rinsed not with just water but also with extra wort sample. Any water residue will dilute the reading and reduce it. Think about it.

 

[tracer bullet]

I dip a small weighing dish into the wort, let it sit for ~ 10 minutes, spot that there's clearly some particulates dropped out, then use a clean finger to place a few drops onto my refractometer. I always get a good reading that matches the hydrometer the half dozen or so times I've compared the two. I get consistent refractometer readings again and again afterwards as well. I shoudl clarify I don't keep measuring the same sample that's been sitting in it, evapoartion or somethign could be a thing, it's a plausible explanation. For subsequent readings I give it a little dip in clean water, wipe that off, then take a new reading from my sample.

I was constantly annoyed by the thing as well, and spent a lot of time figuring out what's up while I stared at a boil kettle without much else for myself to do. This is what fixed it for me. It's sort of... garbage in = garbage out. That's how I took care of the garbage in I guess.

Hydrometer can handle all the junk in it and get a good reading (temp is most important). Refractometer needs a good sample.

 

[tracer bullet]

One other thought, haha, is that of course though this seems to work really well, it does take some time, and may not make the refractometer a super useful tool. Although there's the temperature factor if using a hydrometer that might put them on equal footing.

Not so long ago I was still getting my process figured out and would end up sometimes diluting wort, sometimes adding DME, chasing my tail partly from a constantly evolving process and partly because of the refractometer thing. These days I'm MUCH more consistent, and the gravity reading is more of an afterthought. I always take the reading, but I no longer need to react to what I see. It's more like - "hmm, I overshot it by 3 points, I guess that finer mill setting worked out, I need to remember to drop a quarter pound of grain next time I brew this".

 

[rock_n_herm]

I use a refractometer, in a blue box, bought from lhbs, $45 if I remember correctly. Mine has ATC (auto temperature correct), but sometimes I notice variation in my measurements. That’s why what @dmtaylor says is a good idea. Take 3 measurements and average them.
For pre-boil and original gravities, I use my refractometer and my hydrometer together, and their numbers are usually within a point or two. I just let a few drops fall from the hydrometer onto the refracto plate to make sure I’m measuring the same sample.
Since I make small batches, I rely on my refractometer for final gravity readings, as I don’t want to waste precious beer on hydrometer samples. I have used the Brewer’s Friend wort refraction index (WRI) spreadsheet to come up with a WRI. The WRI is necessary to correct for presence of alcohol so the measurement can be adjusted for final gravity.

 

[bracconiere]

did you wash it after the first sample? and maybe not dry it enough for the second test?

i'm still new to refracs myself....

 

[brewdude88]

I use refractometers and hydrometers for brewing and professionally for measuring jet fuel specs and additives. I highly doubt that there is any hydrometer in the homebrew world that is close to the accuracy of a calibrated ATC refractometer.

Make sure the screen and lense are clean and dry before adding a sample. Also check it's calibration often (there are special solutions you can get to calibrate to a known gravity) don't use distilled water and calibrate to 0, it will probably be off in the range you use it at. I tend to use a standard time of 2 minutes between adding a sample and taking a reading (to give the temperature correction time to stabilize).

 

[DonT]

I've run into this before as well. My usual process is to take maybe an 1/8 to 1/4 cup and place it in the freezer for a couple of minutes to take the heat off. This gives me enough to take a few different readings in case I get something that doesn't look right. I usually just go with best two out of three. I take mash measurements at 10 min intervals to watch the progression. When it evens out... usually around 60 min... it's time to sparge.