Problems using my Refractometer

I just acquired a refractometer for use in my All-Grain brewing productions. I would really like to utilize this tool for quickly checking the gravity of my runnings, and for Pre & Post boil gravity readings. During my last 3 brew sessions I have had stange results. My pre boil gravity will read higher than my post boil. This is not possible.

My refractometer is calibrated reading 0.00 with water.

During my last brew session (yesterday) it read 1.055 pre-boil. Post boil it read 1.048, which is what my hydrometer also read at 60 degrees F.

Whats going on ?? :smack:

I take it the brix are also going down instead of up? Gave both a chance to cool?

yeah i gave it plenty of time. plus 2-3 drops ought to cool pretty quick. Mine reads Specic Gravity and Brix.

My first thought is maybe there's some water in your post-boil sample, from after cleaning off the refractometer? Or maybe some residual water in the dropper? That could explain the original sample being higher (dry refractometer, dry dropper) and the second being lower (a wet dropper, wet lens or lens cover)? When I take samples I usually get as much water from cleaning out of the dropper and then cycle a few squirts to make sure that i've essentially washed the dropper, and make sure the lens is dry on all surfaces.

My guess is that your preboil sample was stratified and you picked from a more concentrated pocket.

I like to use my pocket knife to get a drop or two. It's clean and dry and cool.

I'd agree with Bobby M that you probably pulled a preboil sample from a concentrated pocket / volume. Were you recirculating the mash? Did you pull the sample for preboil when the boil kettle was full, or while it was filling? If you pulled the reading while you were still filling your boil kettle, you most likely pulled a higher concentration, as the preboil gravity will dilute the further you are in your sparge.

I've used mine with perfect results until this last session. It's really a time saver, but this time I got a lower post boil reading like the OP. I don't think temperature had anything to do with it. My guess was I got a pocket of lower gravity wort after I pitched my starter. It wasn't a ton, but the results were a real head scratcher. I started boil at 1.051 and ended around 1.059, but refractometer showed a 12.2?! (1.049)

Anyhow, I grabbed my hydrometer and measured. 1.060 and all was right in thhe world again.

A pocket of lower Gravity?? that sounds a bit far fetched. I recirculated during the entire mash, and stirred my wort before taking the reading. I dip my temp probe in the wort and drip a couple drops on the glass. This has happened twice now, Pre-boil reading higer than the post boil. then the cooled hyderometer sample i take before pitching always matches the refractometer. HUH??

If you take a hot sample of wort (a couple of drops) any evaporation of that sample will cause the reading to be high. I usually put a 2 teaspoon sample in a cool glass for a few seconds until temp is down just a bit and then take a few drops from that sample. You have less evaporation and a better reading.