Inconsistent Boil-offs.

Hi all,

Just finished up my 4th AG batch today and loving it.

So far I have hit my pre-boil gravities every time, but I have been getting inconsistent boil-off rates. I usually lose 1 gallon for a 60 min boil, and that has stayed pretty much the same.

But the last 2 batches I did (Walkers 80 /- and BierMunchers Cream of 3 Crops) called for a 90 minute boil.

Well the 80/- became a wee heavy as i went from 7 gal to 4.5 gal (loss of 2.5 gallons) and the Cream of 3 Crops had to be topped up 2 gallons, as I went from 6.75 gallons to 3.5 gallons (loss of 3.25 gallons)

I don't understand why another 30 minutes would cause so much more loss. I'd really like to be able to hit my target volumes, but don't know how to calculate it when my numbers are so far off.

Please help!

maybe the amount of flame/heat is different

The less liquid you're boiling the faster it boils off. That'd be my guess.

@ lumpher, I'm not sure. I had the the wide open on every brewday. That's the only way I get a nice blue flame.

@ Loapathy I can see that, but I still have a difference of .75 gallons on the 90 min. boils.

Are you using the same boil kettle for each session?

Not 100% on this, but humidity might have an effect on boil-off rate

@ Heyyo, yeah, it's the same kettle.

Are you brewing outdoors? There are a million things that can effect a boiloff rate, humidity, air current on the flame, air current on the surface of your wort, outdoor temp to name a few. If you those things aren't constant, you will get some different boil off rates. If I had to guess and you are brewing outdoors, yours is probably the air current on your flame. You can build a wind screen to help that.

By the way, boil-off rate is fixed, you don't boil off more with less wort. And it is not a %, as beer smith likes to trick you into thinking.

You could also get a big metal ruler and mark the 5 gallon mark, take a small sample and see if your at your og.

HarkinBanks said:

Are you brewing outdoors? There are a million things that can effect a boiloff rate, humidity, air current on the flame, air current on the surface of your wort, outdoor temp to name a few. If you those things aren't constant, you will get some different boil off rates.

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Yes, I am brewing outdoors. I keep the stand in the garage with the doors up. I've sot some scrap aluminun flashing, I'll have to try making a wind screen as you suggest. Thanks!

JasonToews said:

You could also get a big metal ruler and mark the 5 gallon mark, take a small sample and see if your at your og.

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I have a sight gauge, so I'm aware of the volume. But can't changing the boil times affect the taste of the beer? Namely hop utilization.

hmm yes your right. Well I hope you figure it out!

JasonToews said:

You could also get a big metal ruler and mark the 5 gallon mark, take a small sample and see if your at your og.

Click to expand...

not a bad idea, but also want to make sure your temp correcting for the less dense hot liquid.

My guess its the outside temp. I also boil in the garage with the garage door open and I was getting 20% boil off rates instead of the "typical" 15%. However, this last brew I got 15% boil off rate and the only thing I can think of is that it was about 10 degrees or more warmer than the previous brews. Just my 2 cents worth...

sjbeerman said:

the only thing I can think of is that it was about 10 degrees or more warmer than the previous brews. Just my 2 cents worth...

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10 degrees WARMER!?! Must be nice. We're getting ready to get about 8"-10" of snow here.

As the level of wort decreases the boil will become more intense if you are not lowering the amount of heat applied. Less volume to heat hince greater boil off volume after the first 1 gallon loss at hour one. I would suggest lowering the applied heat until you get a consistent boil off rate over 90 minutes.

Its probably the cold dry weather we are getting this winter up in the north. I'll probably get a 25% boil off on saturday. Gonna brew in garage (doors open for ventilation) and it will be a wopping 0 degrees outside. sweet!!