Insane evaporation rate

Hi all....after coming short on my post boil volume during my 1st brew with a new Polarware 15-gallon pot I decided to do a boil test to see how much I would lose in the future. I filled the pot with 8 gallons of water and brought it to a boil...I guess you could say a rolling boil. I let it boil for 1 hour and at then of the boil, using a dip stick I made when filling the pot, I ended up with 6 gallons. That seems ridiculously high to me. I was wondering what the average loss is and what I can do to bring my loss way down. I read in an old BYO article that a good evaporation rate is 6-8%....mine was 25%!!!! Any advice?? Thanks

Yeah, that does seem a tad high. Are you sure your readings were correct? Did you cool the water before measuring?

You can't really use % to calculate evaporation.
A lot of factors will play a part including humidity, ambient temp, and shape of your boil kettle.

A big factor is the the amount of your wort surface that is exposed to the ambient air... imagine boiling 5 drops of water in a frying pan for an hour... you'd have 100% evaporation.

If you found you lost 2 gallons an hour, I doubt it will change much whether you boil 6 gallons or 10.

So, the advise is, test it, measure it, and account for it in future boils. Keep in mind, how hard you boil, temp and humidity changes will impact future boils.

Good luck

Ed

No, I didn't let it cool..but even with expansion and contraction...doesn't 2 gallons/hour seem high? I'm pretty sure on my numbers. I added the water 1 gallon at a time and each time I made a mark on a stick, so I'm fairly confident in the measurements. I just read a post on Beer Tools forum. The guy there had the same question about the same pot and he came out with the same rate..25%...he boiled 4 gallons for an hour and lost 1.

That's the same evaporation I experience. I always start with 7.5 gallons preboil to hit 5.5. I just did a 90 minute boil today on a barleywine and started with 8 gallons to get down to 5.5. It took me quite a few batches to accept the fact that I boil off 2 gallons in an hour.

The Polarware pot is fairly wide, 18.5". As soon as I saw the pot and how wide it was I knew I was going to lose quite a bit during the boil, I just didn't think it would be that much. I don't have a problem accounting for it in the future my concern is that I had read that that kind of a loss could cause flavor problems in the finished product...

A 2 gallon loss in a 15 gallon pot during a 1 hour boil is not out of line.

Ok, well I see from the couple of responses I got already that this could be "normal" for my system and will that I will have to take it into account in the future.

Thanks for the input guys...I appreciate it

Wino24 said:

The Polarware pot is fairly wide, 18.5". As soon as I saw the pot and how wide it was I knew I was going to lose quite a bit during the boil, I just didn't think it would be that much. I don't have a problem accounting for it in the future my concern is that I had read that that kind of a loss could cause flavor problems in the finished product...

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Evaporation won't have a negative impact on your end result. Trying to "fix" the evaporation by covering the pot can have negative impact.

Your best bet is to "learn" what your loss will be and start with enough volume to account for it.