Question RE Refractometer Reading

[ircbrewing]

So I brewed a red rye IPA Sunday. My numbers to hit were OG 1.070 and FG 1.018 (TBD). I took my pre-boil gravity where I had approximately 6.8 gallons of wort had a reading of 1.050, which was a little low, but within 5 points of where it should have probably been which is fine with me.

However, when the boil was done and the volume had decreased to around 5.5 gallons, my OG and the wort cooled my sample was 1.042. I took 2 readings because I couldn't believe it. If your preboil gravity is 1.050 and you concentrate the wort by boiling off additional water, how can gravity drop 8 points? Per brewersfriend calculations, if my preboil wort was 1.050 with 6.8 gallons and my target ending volume was 5.5 gallons (leaving .5 gallon to trub loss so final 5 gallon batch to fermentor) my gravity should be around 1.062. Really confused and those readings don't make sense.

Now....I soak my refractometer thief in starsan for the cooled sample collection. I try to shake and squeeze it all out, but the thief is cheap plastic and has a crack in air bubble used for squeezing and pulling the sample so it doesn't really work. Is additional water stuck in the their diluting my sample? I mean even just a half a drop of starsan solution stuck in the thief with a drop of wort can have a big impact.

At the end of the day it's beer, but this has been annoying me for 3 days, so any guidance is welcome.

 

[hottpeper13]

If you're going to use a refrac ,take the sample while sanitizing the wort chiller. I take a cup of preboil wort and chill it for my hydrometer, and when trasnsfering wort from kettle to fementer I collect the last truby part for the hydrometer. For the most part I leave the refrac on the shelf.

 

[kh54s10]

It is pretty simple. Your gravity after the boil cannot possibly be lower than before the boil, unless somehow water was added. So, one of the measurements was in error.

I use a sanitized spoon to dip out a sample for the refractometer.

 

[ircbrewing]

I figured. I should have broke out the trusty hydrometer after I suspected an error on the refrac. Sometimes...if it aint broke...

I'll not use the cheap broken thief any longer and take the sample at flame out. I'll just go with brewers friend's calculation of OG and disregard my false readings. 1.062 it is!

 

[Sailingeric]

I have had that happen a couple of times. What I do now is take my dropper that I use to get my sample and I do a doze or so squeezes to make sure any sanitizer is out of it.

 

[RM-MN]

You don't need to sanitize your sample dropper. The wort is near boiling. It will kill any detrimental bacteria on contact. You don't return the sample to the pot and if you did and it had bacteria they die instantly anyway. My refractometer has temperature correction built in and with only a drop of sample it cools it off very quickly so I don't cool the sample at all. When the wort it cooled I may take another sample (pretty rare) and when I compare that reading with the hydrometer they match. For the chilled sample, dip the dropper in sanitizer and take the sample. You will only have a few drops and won't be returning that to the wort so the chance for infection are incredibly low.

 

[IndyBlueprints]

I don't have any evidence of this, but I have heard that if a boiled wort has a chance to settle down, that some of the sugars may drop to the lower portion of the volume, leaving the upper portion with a lower SG than what is accurate. However, if it's at a rolling boil, that won't be the case.

 

[ircbrewing]

You don't need to sanitize your sample dropper. The wort is near boiling. It will kill any detrimental bacteria on contact. You don't return the sample to the pot and if you did and it had bacteria they die instantly anyway. My refractometer has temperature correction built in and with only a drop of sample it cools it off very quickly so I don't cool the sample at all. When the wort it cooled I may take another sample (pretty rare) and when I compare that reading with the hydrometer they match. For the chilled sample, dip the dropper in sanitizer and take the sample. You will only have a few drops and won't be returning that to the wort so the chance for infection are incredibly low.

I was actually taking the sample after the beer had cooled down right before racking to bucket. Well aware of hot wort being sanitary.

 

[eric19312]

If you're going to use a refrac ,take the sample while sanitizing the wort chiller. I take a cup of preboil wort and chill it for my hydrometer, and when trasnsfering wort from kettle to fementer I collect the last truby part for the hydrometer. For the most part I leave the refrac on the shelf.

I do this exactly

The preboil wort takes time to chill so I do a refractometer measurement there just to make sure I am in ball park. If I am too low or too high I will adjust the boil to make sure I end up at right OG.

I get my OG sample from the pump and the kettle kettle recirculation hoses. Its just about right volume and otherwise would end up on floor of garage.

 

[Redleg84]

I believe the same thing happened to me on my last batch. My pre boil SG was right on, as was my boil off amount, but my OG was 5 points low. I figured it was probably because of of a diluted sample.
I'm going to take the sample when I throw in the chiller on this next one.
Does having trub in the sample throw off a refractometer reading?