Hit preboil gravity, missed OG

[mscg4u]

Okay so this is the second batch I have had this happen with... I hit, and exceeded my pre-boil gravity (estimated 1.038, actual 1.044). Volume was 6.5 gallons. Went through boil, cooled, ended up with around 3.25 gallons (was supposed to be a 3.25 gallon batch) at 1.063... my estimated OG was 1.074... Now from my understanding the pre-boil gravity measures my mash efficiency...the SG after boil measures my overall efficiency... I just don't understand how I can hit the pre-boil, end up with the exact amount of wort I want, and miss my OG by 11 points.

For reference, this is my 3rd all-grain. My first was another 3 gallon batch in which I missed my gravity by 6 points, but hit my pre-boil gravity (same issue as now). My second all-grain batch, 5 gallons, hit everything perfectly.

I used a hydrometer, yes I cooled/corrected for temperature...

 

[mscg4u]

Anybody?

 

[Rbeckett]

Seems like an excessive amount of boil off to me. And if the preboil was1.044 I would have expected the post boil to be higher, especially with that much boil off from the kettle.
Bob

 

[ajf]

Where did you measure your pre-boil gravity? In the kettle, after the sparge?
I have difficulty on believing that you can boil down from 6.5 gallons to 3.25 gallons in a reasonable time. I think you are losing wort between finishing the boil, and transferring to the fermenter. It could be due to leaving trub behind in the kettle, hop absorption, or dead space in the equipment. All of those will cause you to leave sugars in the kettle.

-a.

 

[mscg4u]

I'm not losing wort; I siphon it straight from the kettle to the fermenter, and I took the sample from the kettle, and took another from the fermenter to use my other hydrometer and see if that was the problem. As for the boil off, it was a 90 minute boil and I always have a lot, my kettle is really wide. I'm as perplexed as you guys are.

 

[Kyled93]

Silly question, but I assume you are boiling without a lid?

That being said can you explain your setup?

 

[BrewKnurd]

The math doesn't even come close to working on that. If you have 6.5 gallons at 1.044, and you boil off half of that, you would be in the neighborhood of 1.088. As ajf said, the only way this makes sense is if you are leaving liquid volume behind somewhere. Absorbed into hops, left behind in the kettle, something.

 

[Newbeerguy]

Are you checking your pre boil gravity before you sparge? Doesn't make much sense... You are cooling the samples to 60 degrees before measuring? Your volumes are spot on?

 

[mscg4u]

I mash with a 5 gallon cooler, false bottom. Batch sparge, drain directly into the kettle. It's a 10 gallon kettle, pretty wide. I'm not sure what kind of burner I have, not that it really matters. I do my boil, cool with an immersion cooler, usually take my sample for my hydrometer reading before I transfer, whirlpool, then siphon into my fermenter. I leave behind only the thickest trub in the kettle, less than .25 gallon.

 

[mscg4u]

I do take a preboil gravity reading, it was 1.044... And I know my volumes are good, I sat there with a measuring cup and my old plastic paddle and cut grooves into it every half gallon.

 

[Erroneous]

I recommend calibrating whatever you use to measure the volume. How I did that is by weighing 16 ounces of ro water at room temp at sea level. Then I marked that on a plastic cup and made a measuring stick for my keggle. Afterwards measure your boil off rate. I bet that will help.

Edit just saw your post about volumes. Kitchen measuring cups are notoriously bad at being off. Recommend weighing.

 

[mscg4u]

I take my gravity reading after I sparge... Why would I take my preboil gravity before I sparge?

 

[mscg4u]

It wasn't that off because I ended up with 10 gallons in my 10 gallon kettle.

 

[Erroneous]

You are correcting your hydrometer for temperature right?

If everything else is calibrated and your observations are accurate then science is broken and we need to pray to trees again

 

[Newbeerguy]

I take my gravity reading after I sparge... Why would I take my preboil gravity before I sparge?

Well, you typically wouldn't, but that would be one reason to account for a higher than anticipated pre boil gravity and a subsequent low post boil gravity.

 

[mscg4u]

I did adjust for temperature/cooled it down to 60 degrees. I really have no clue... It makes no sense and I don't understand what I could be doing wrong.

 

[mscg4u]

It couldn't be the .25 gallon I am leaving behind? I mean aren't the sugars in wort evenly distributed throughout?

 

[BigBlueDog]

If you don't thoroughly mix the first runnings from the mash tun with your subsequent sparge collection(s), your per-boil SG could be off the mark.

 

[BrewKnurd]

It couldn't be the .25 gallon I am leaving behind?

No.

I mean aren't the sugars in wort evenly distributed throughout?

Yes.

The .25 gallons you leave behind account for some lost sugars, but not to the tune you're talking about here.

 

[Newbeerguy]

What was your recipe?

 

[HIlife]

I think Big blue dog is right, you probably got your hydro sample from a more dense section of the runnings.

 

[mscg4u]

Is there a way to backtrack from my post-boil gravity and determine what my Pre-boil gravity should have been if everything is correct?

 

[Newbeerguy]

Is there a way to backtrack from my post-boil gravity and determine what my Pre-boil gravity should have been if everything is correct?

Yep, but we need to know the recipe.

 

[mscg4u]

3.25 lb wheat malt
2.6 lb Munich 1
1.3 lb pilsner 2 row
.65 lb crystal 40
.65 lb toasted wheat (30 min @ 350)
1 oz tettnang 90 min
.25 oz tettnang 30 min

I have beer smith and it says the estimates preboil gravity should have been 1.039, and my OG should have been 1.075. So even if I was off on my preboil, I messed up somewhere.

 

[Newbeerguy]

3.25 lb wheat malt
2.6 lb Munich 1
1.3 lb pilsner 2 row
.65 lb crystal 40
.65 lb toasted wheat (30 min @ 350)
1 oz tettnang 90 min
.25 oz tettnang 30 min

I have beer smith and it says the estimates preboil gravity should have been 1.039, and my OG should have been 1.075. So even if I was off on my preboil, I messed up somewhere.

I really quickly plugged these numbers into beersmith as well and I got (with my equipment) for a 3.25 gallon batch a 1.048 Preboil and 1.067 Postboil.

Man you got me stumped.....you are 100% confident in your readings/volume?

 

[mscg4u]

That's weird, maybe I need to readjust my beersmith profiles because if that is the case then I would be spot on, just a couple points shy.

 

[Newbeerguy]

That's weird, maybe I need to readjust my beersmith profiles because if that is the case then I would be spot on, just a couple points shy.

Yeah. You know your setup better than anyone, but without changing anything in mine except for batch size, those were my numbers. Your right, according to my numbers, you're not far off. I'd do another batch and see where you stand. It took me about a dozen batches to get beersmith perfectly dialed into my setup. Either way though, the recipe looks solid and I am sure it will turn out good for you.