Estimating boiloff rate for new kettle

Tonight I'll be brewing the first batch in my new 10 gallon Winware kettle from amazon. I've been doing partial boils and smaller 3-gallon BIAB batches in my 5-gallon stainless starter kettle, but this will be my first full 5.5-gallon BIAB batch.

I'm trying to estimate a boiloff rate for the new kettle. I've used Brewer's Friend to get the rate pretty dialed in on my old kettle at 2.3 qt/hr. Since this new kettle will have a larger surface area, I'm expecting a higher boiloff rate.

I calculated the area of each kettle (thanks high school geometry) and then calculated the proportional difference (thanks high school algebra) to get 4 qt/hr for the new kettle.

Does this sound like a reasonable approach? I know I'll have to dial it in by trial and error but I'd like the closest starting point possible. It's the same gas burner on my stove (unless the new kettle is wide enough to cover 2 burners). I guess if anything, I'd rather underestimate the rate and add topoff water at the end, rather than having to extend the boil to reach target volume and OG.

Thanks!

1 gallon is a reasonable guess. Most people see something in the 1-1.5 gallon/hr in comparable sized kettles.

Have you tested to see if you can even boil 6.5 gallons on your stovetop? Some stoves can do it but certainly not all.

I just fill a couple gallons in a new pot and boil for a half hour. See how much you have boiled off and multiply by two

Thanks for the responses. I haven't had a chance to test it but from the research I've done on these boards, I think my modern gas range with power burner (15k BTU I think) will be able to do it, especially if I can get the kettle to cover another burner also.


Testing with water also sounds like a good idea, although I probably won't have time before brewing tonight.

Anyway, thanks again.

Yeah, don't take the chances to estimate. Just pretend it's brew day and boil a certain amount of water for a half hour (multiply by 2), or an hour at the same vigor of a brew day. That's the only sure way to know.

It's going to be close to a gal per hr likely. If you figure for 1 gallon and you're between .75 and 1.25 gal per hr you're talking about 1.003 difference in gravity or so on a 5 gal batch. I'd say go for it, measure this time, then go from there.

Boil off rate is proportional to volume as the intensity of the boil will increase as volume decreases given a constant kW/h

Queequeg said:

Boil off rate is proportional to volume as the intensity of the boil will increase as volume decreases given a constant kW/h

Click to expand...

I think most folks adjust the heat to achieve the same level of rolling boil, so in practice the boil off rate is pretty much constant for a given pot/surface area regardless of how much is in the pot.

So, the new kettle is awesome, and my first full-size BIAB batch went really well. I estimated the boiloff rate at 1gal/hr, and nailed the volume into fermenter and OG perfectly. Recipe called for 5.5gal at 1.052 and that's exactly what I got. Sweet.

My stove was able to do a soft boil with one burner, and a decent rolling boil with 2.

Only annoying part of the night was trying to squeeze the bag after the mash - I used to put it in a colander and press down with the kettle lid, but with 10.5 lbs of grain it couldn't really be contained in the colander, so I need to figure something else out. Hanging the bag is not really an option in my kitchen.

Thanks for everyone's input.

I put a metal rack over the kettle to rest the bag on... I use an old one I had laying around, but something like this should work too if you find the right size for your kettle:

http://ecx.images-amazon.com/images/I/71igHe0NZHL._SL1280_.jpg

Once it's mostly squeezed out, it'll sit in the colander a little easier. I use one like this:

http://previews.123rf.com/images/eu...tic-colander-isolated-on-white-background.jpg

It's the right size so that it sits on top of my smaller dunk-sparge kettle.

Wilserbrewer once suggested hiding a pulley mount point inside the cabinet over the stove. I haven't done it yet, but I'll probably try it at some point. Unseen and out of the way...

jbedell2 said:

So, the new kettle is awesome, and my first full-size BIAB batch went really well. I estimated the boiloff rate at 1gal/hr, and nailed the volume into fermenter and OG perfectly. Recipe called for 5.5gal at 1.052 and that's exactly what I got. Sweet.

My stove was able to do a soft boil with one burner, and a decent rolling boil with 2.

Only annoying part of the night was trying to squeeze the bag after the mash - I used to put it in a colander and press down with the kettle lid, but with 10.5 lbs of grain it couldn't really be contained in the colander, so I need to figure something else out. Hanging the bag is not really an option in my kitchen.

Thanks for everyone's input.

Click to expand...

You could always convert a 8-10 gallon igloo cooler into a mash tun for $70-80. Not a huge investment if you don't want to worry about bags.

Queequeg said:

Boil off rate is proportional to volume as the intensity of the boil will increase as volume decreases given a constant kW/h

Click to expand...

Sorry, that's not how boiling works. I takes a constant amount of heat to boil off (vaporize) 1 gal (the latent heat of vaporization), no matter how much liquid is in the BK. There will be a small difference in the amount of heat lost from the sides of the BK at different fill levels, but that is a minor effect. So, for a constant heat input, the boil off rate is almost constant. It is definitely not proportional to the volume of liquid. Check your physical chemistry textbook.

Brew on