Pre and post OG puzzle
- Thread starter Yola
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It isn't possible for the gravity to do anything but go up as you boil off water.
The only explanation is that you haven't got an accurate and representative sample. In simple terms, it wasn't properly mixed or you have mismeasured.
Mismeasured can include not allowing for temperature corrections, but when the preboil gravity is higher than the post boil, the first thing that comes to mind is that the wort wasn't mixed and where you took the sample from was heavier than the average - a good stir with a spoon/paddle and returning a couple of hundred mills to the kettle before taking a sample from a tap is a good idea.
Mark
The only explanation is that you haven't got an accurate and representative sample. In simple terms, it wasn't properly mixed or you have mismeasured.
Mismeasured can include not allowing for temperature corrections, but when the preboil gravity is higher than the post boil, the first thing that comes to mind is that the wort wasn't mixed and where you took the sample from was heavier than the average - a good stir with a spoon/paddle and returning a couple of hundred mills to the kettle before taking a sample from a tap is a good idea.
Mark
Danscraftbeer
Well-Known Member
Its a miss reading on the pre boil gravity. I gave up on it as a waste of time and confusion testing for a pre boil gravity reading.
Forgot how many times I've posted that. Its a wasted time of confusion.
It throws you into total confusion.
Forgot how many times I've posted that. Its wasted time and confusion.
Forget it and watch how your brew software tends to be very close to total end results.
No knee jerk reactions the end result then continued is your process, and end results on the calculations etc.
$0.02
Forgot how many times I've posted that. Its a wasted time of confusion.
It throws you into total confusion.
Forgot how many times I've posted that. Its wasted time and confusion.
Forget it and watch how your brew software tends to be very close to total end results.
No knee jerk reactions the end result then continued is your process, and end results on the calculations etc.
$0.02
Danscraftbeer
Well-Known Member
and/or misreading OG gravity. I have found that the best readings are taken with thorough mixed pithed pre ferment test.
Letting the wort settle over night then taking a reading can lead to a miss reading. Sugars can sink post wort but they seem to float pre boil?
Anyways its about getting correct readings I think.
Letting the wort settle over night then taking a reading can lead to a miss reading. Sugars can sink post wort but they seem to float pre boil?
Anyways its about getting correct readings I think.
Rocker1986
Well-Known Member
Once sugars are dissolved in solution and evenly mixed, they don't precipitate out unless it reaches saturation point and the concentration in the average wort is nowhere near that. If they did, then the beer in the keg would change flavor and color as it got emptier because there should be less sugars at the top than the bottom, but as we know this does not occur.
The pre-boil wort may not have had the sugars evenly mixed, but I honestly don't understand how anyone could have such a problem taking accurate pre-boil readings once you know this kind of stuff. All it needs is a bit of a stir, or just bring it to the boil and take the sample of wort just as it begins boiling. I get consistent pre-boil readings every batch that always line up properly with the post-boil readings. It's not rocket surgery.
The pre-boil wort may not have had the sugars evenly mixed, but I honestly don't understand how anyone could have such a problem taking accurate pre-boil readings once you know this kind of stuff. All it needs is a bit of a stir, or just bring it to the boil and take the sample of wort just as it begins boiling. I get consistent pre-boil readings every batch that always line up properly with the post-boil readings. It's not rocket surgery.
klangers
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The only thing that makes pre-boil gravity hard is the cooling of the sample whilst minimising evaporation. Otherwise it's exactly the same as any other gravity reading. Personally I use a refractometer which makes things a little quicker, and once you get the hang of how to cool your sample (I use shot glasses left in the freezer) it's a real piece of cake. Just skim a sample off with the shot glass, let it sit for a minute to cool in the cold glass then dip your refracto in.
IMO it's a useful measurement, as you can adjust your boil time to make up for "lost" gravity.
Stratification can be really intense, especially if you do a big old sparge.
IMO it's a useful measurement, as you can adjust your boil time to make up for "lost" gravity.
Stratification can be really intense, especially if you do a big old sparge.
Rocker1986
Well-Known Member
I have a borosilicate glass hydrometer testing jar that I use for pre-boil samples. I used to take them just as the boil started but now I just mix the wort up with the wire brush when I clean off the urn element after mash out, take the sample and stick it in the fridge to cool it down quickly. The reading is taken just as the boil begins, then the wort is tipped back into the urn. I usually mix it up a bit with the hydrometer too when I take the reading, no trouble at all.
This is why refractometers are labelled "auto temp correction" or ATC.RdeVjun said:
The sample is so small that the temp equalises with the refractometer almost instantly. It's more important to have your refractometer at the right temp, especially if you brew outside. If the device is at an ambient 10 degrees you will get a different reading compared to an ambient of 35.
klangers
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Your refracto won't stay ambient very long if it keeps equalising with hot wort.Lionman said:
If you're doing any kind of reliable measurement, you'll be doing it multiple times. Hence cooling the sample. Whatever works for you to get a reliable and repeatable measurement.
I'm not sure about your technique, but I can't see the possibility of my refractometer moving even a fraction of a degree Celsius when I take readings. The refractometer is a solid hunk of stainless steel and glass - weighing in at 275g. I take samples using a pipette and the two drops of wort required to get a reading would be less than 500mg. Once the drops are on the glass, I put the cover on and take a reading straight away. You are not doing anything silly, like dunking the instrument in hot wort, are you?klangers said:
As long as your tools are calibrated and you have a good sampling technique, refractometer readings are quick, accurate enough for the purpose and very informative. Just remember to either stir or understand what you are sampling. Clearly there will be difference between first runnings and the end of sparge. You may be interested in end of sparge SG (possibly to decide when to stop), but if your goal is to take pre-boil gravity reading, you must stir the entire volume before you take a sample.
