[Thirsty_Monk]

I use hydrometer all the way thru.
Hydrometer is only for glycol checking.

[a10t2]

I stirred the wort in the boil kettle after sparging and took a sample.  My refractometer read 1.032!  It should have been 1.041.

IME, stirring isn't enough. You can't get an accurate pre-boil gravity until just after the boil starts, whether you're using a hydrometer or refractometer.

[yso191]

I stirred the wort in the boil kettle after sparging and took a sample.  My refractometer read 1.032!  It should have been 1.041.

IME, stirring isn't enough. You can't get an accurate pre-boil gravity until just after the boil starts, whether you're using a hydrometer or refractometer.

But sample 2 & 3 were post start-of-boil. Regardless, the refractometer is wildly innacurate.  And I calibrated it after these samples.  It zeroed perfectly.

[klickitat jim]

I only use my refractometer to sort of confirm conversion/extraction and occasionally to get an idea of preboil. For example at X quarts per pound it should be X brix. If it's well below that then I keep at it.

[case thrower]

I stirred the wort in the boil kettle after sparging and took a sample.  My refractometer read 1.032!  It should have been 1.041.

IME, stirring isn't enough. You can't get an accurate pre-boil gravity until just after the boil starts, whether you're using a hydrometer or refractometer.

Why can't you get an accurate gravity measure until the boil starts?

And someone asked in another thread why you don't like Chico.  What are your thoughts on Groucho and Harpo?

[HoosierBrew]

+1 to taking your preboil sample after reaching a steady boil to get uniform mixing. Steve, I saw that your measurements were 1.041, 1.043, and 1.055. Let's throw out the 1.041 since it was taken before reaching boil.  How close together time wise were the last two taken ? Evaporation would obviously concentrate the boil and increase your readings. I just ask because on my system my preboil (on a 60 minute boil) is usually ~ 12 pts lower than my post boil OG, the difference between your last 2 readings.

[denny]

I stirred the wort in the boil kettle after sparging and took a sample.  My refractometer read 1.032!  It should have been 1.041.

IME, stirring isn't enough. You can't get an accurate pre-boil gravity until just after the boil starts, whether you're using a hydrometer or refractometer.

Agreed.  I found that through experience.

[denny]

Why can't you get an accurate gravity measure until the boil starts?

Because the higher gravity wort from the mash and the lower gravity wort from the sparge aren't well enough mixed.  The first runnings, containing more sugar, are heavier and sink to the bottom of the kettle.  The only way to get them well mixed is to wait til the boil mixes them.

[case thrower]

Why can't you get an accurate gravity measure until the boil starts?

Because the higher gravity wort from the mash and the lower gravity wort from the sparge aren't well enough mixed.  The first runnings, containing more sugar, are heavier and sink to the bottom of the kettle.  The only way to get them well mixed is to wait til the boil mixes them.

Wow.  I had no idea.  What about taking a reading on just the first runnings?  Would the sugars from that still be mixed in the wort or do they pretty much fall to the bottom and sit?  I generally take a reading from the cooler (doing small batches in a 5 gallon Igloo water cooler) after 60 minutes.  Depending on where I get the sample from, my numbers can be all over the place.  My current SOP now is to stir the mash really well and then get the sample.  After I've drained the mash, I give that a vigorous stir and then take a sample from what's in the kettle.

[a10t2]

Why can't you get an accurate gravity measure until the boil starts?

Like Denny said, the wort will start out stratified (unless it's a no-sparge beer), and no reasonable amount of stirring will get it well-mixed. This could actually be a case where a hydrometer would give better results, due to the larger sample size.

In practice I just measure my first and second runnings with the refractometer and math the pre-boil gravity.

And someone asked in another thread why you don't like Chico.  What are your thoughts on Groucho and Harpo?

"Je suis Marxiste, tendance Groucho."

[a10t2]

What about taking a reading on just the first runnings?  Would the sugars from that still be mixed in the wort or do they pretty much fall to the bottom and sit?  I generally take a reading from the cooler (doing small batches in a 5 gallon Igloo water cooler) after 60 minutes.  Depending on where I get the sample from, my numbers can be all over the place.

That isn't stratification, so it must just be a mash that isn't fully incorporated. Do you also see temperature variations throughout the mash bed? I stir continuously during mash-in, about 3-5 minutes, because that's what it takes for me to get a uniform mash temperature.

Regarding gravity readings on the runnings, I take those shortly after starting vorlauf, partly because it's easier that way and partly because it lets me check for conversion efficiency while there's still time to do something about it.

[Stevie]

In practice I just measure my first and second runnings with the refractometer and math the pre-boil gravity.

Good idea, but that assumes semi-accurate volume measurements.

[a10t2]

Good idea, but that assumes semi-accurate volume measurements.

True. I just haven't had to worry about that since I marked my Brewin' Stick™ seven or eight years ago.

Actually, since I do equal runnings, I just average the two readings, which is nice because I can do it in my head.

[Stevie]

My runnings are always ballpark. Within a quart I'd say.

[yso191]

+1 to taking your preboil sample after reaching a steady boil to get uniform mixing. Steve, I saw that your measurements were 1.041, 1.043, and 1.055. Let's throw out the 1.041 since it was taken before reaching boil.  How close together time wise were the last two taken ? Evaporation would obviously concentrate the boil and increase your readings. I just ask because on my system my preboil (on a 60 minute boil) is usually ~ 12 pts lower than my post boil OG, the difference between your last 2 readings.

The first was 1.032 pre-boil, then the post-start-of-boil two were 1.043 & 1.055.  The later two were maybe 10 minutes apart because I wanted to let the samples cool prior to testing.

I'll probably keep using it to see if I can establish a pattern.