Bad Refractometer Readings

[Clint Yeastwood]

I have a cheap refractometer. I brewed night before last, and I was adding boiled water to the wort to get the gravity down. The values I got varied. Sometimes they went up when they should have gone down. In the end, I gave it my best guess.

I have found that this refractometer works best when I squeeze the lens down on the window and hold the refractometer close to a light source. This didn't seem to work all that well for this session.

I stirred the water into the wort before taking measurements, figuring I didn't want to measure the gravity of the water I just poured in. I wanted everything mixed.

Is it possible I got bad readings because I stirred up junk from the bottom of the Braumeister? Wort with stuff suspended in it would be heavier.

 

[rawlus]

if the wort is not stratified and well mixed before measurement a bit of particulate should not affect readings.

most refractometers can be calibrated with distilled water.

i put my iphone camera up to the lens of the refractometer and snap a pic under very bright light (to get maximum contrast)… the resulting picture is easier for me to count the fine hairline increments. during or post-ferment of course the brix value must be adjusted but i use the calculator in Brewfather app to do that.

i have a few precision hydrometers from wine making days but do t use them all that often, i’ve been pretty successful simply using refractometer for most/all of my gravity measurements after running both refractometer and hydrometer measurements against each other over several batches to understand what deviation of accuracy issue existed and for me and my brewing, i don’t feel like I lose a lot of precision using only the refractometer.

 

[Hoochin'Fool]

I have a cheap refractometer. I brewed night before last, and I was adding boiled water to the wort to get the gravity down. The values I got varied. Sometimes they went up when they should have gone down. In the end, I gave it my best guess.

How hot was your wort? I've been tricked by this myself, accidentally added a little too much water, so figured I'd just boil UNTIL the wort reached the expected pre-boil gravity, and then commence with the 60 minute hops, etc. I noticed that taking a small sample (with a spoon) and testing, letting the spoon cool a bit, and then testing again, the gravity would jump up by several points from the first test. At the time, I assumed it was kind of like how hydrometers read lower than true gravity with a hot sample.

Turns out, there was just enough evaporation going on while that spoonful cooled that was messing up my readings.

 

[Clint Yeastwood]

I wondered if the heat of the wort was an issue. I guess it was 175-185, depending on which sample.

 

[Hoochin'Fool]

Shouldn't be much evaporation going on at that temp, must be something else...

 

[DBhomebrew]

ATC, automatic temperature control, refers to the tool's temp not the sample's. Best to collect your sample, hold it in a covered vessel to prevent evaporation, apply the sample to the refractometer once the sample is at the refractometer's temp.

When you're talking about a film of wort on the glass, 175° is plenty warm enough to speed evaporation. Think surface area against volume.

 

[Clint Yeastwood]

First time I've had this problem, which is strange, because I always do it like this.

 

[day_trippr]

Shouldn't be much evaporation going on at that temp, must be something else...

I disagree.

When you're talking about a film of wort on the glass, 175° is plenty warm enough to speed evaporation. Think surface area against volume.

Exactly.

Cheers!

 

[Beekeeper]

Though the refractometer requires little, you can freely take a larger sample, allow it to cool off considerably, take your reading, and pitch the rest of the sample back into the boil. This helps avoid the change in gravity due to slight evaporation that occurs when using a tiny amount.

 

[Clint Yeastwood]

I don't think evaporation is the problem. The wort goes on, the lens slams shut...not a lot of time involved.

 

[DBhomebrew]

Many of us have found a set of best practices that lead to consistent and reliable refractometer readings. Those include collecting a quality sample representative of the full wort, bringing it to a stable temperature matching that of the refractometer's (also at a stable temp) before applying it to the glass, and protecting it from evaporation while doing so. YMMV.