evaporation

[Graeme]

I've recently got a new stainless steel kettle that is double the size of my last and I am trying to work through some of the issues, well one issue: evaporation. I was a little worried about the evaporation rate on this boiler. It has an element fitted to it and it's allot more powerful than my last one so

I gave it a test run with 25 liters (This would be a usual pre boil volume for 90minutes on my old system for a 20 liter batch). The boil off rate was pretty high and I lost 6 liters over the 90 minutes.

I figured this in to the equation on brew day and rather annoyingly my losses were nowhere near what they were on my test run and I lost 10 gravity points. I realise now that for a good portion of the boil I had the kettle lid on 3/4 so that didn't help. I also realise this isn't ideal as you need to drive out DMS.

Even with the lid on like that, loosing only 3 liters is confusing. I amost feel silly typing this but it is something I wondered: Being allot denser, does wort evaporate differently than water?

Thanks for your help

G

 

[wickman6]

I have wondered if water boils off at a digfferent rate than wort as well. I'm interested to see what others might have to say.

 

[zachdotcom]

Does anyone have an answer for this?

 

[duboman]

You are not boiling off(evaporating) wort, you are boiling off the water in the wort, so the answer is no.

You need to regulate the heat so you get a nice rolling boil, you don't need such a vigorous boil as to drive off more than necessary. This is a common problem when people move to big burners.

Other factors such as humidity and temperature will effect your rate of boil off as well to some degree. Also, low, wide kettles tend to boil off more than high narrower kettles due to surface exposure.

It will take a couple batches to dial this in so just keep an eye on your boil. Once the wort begins boiling you can lower the heat to the point of getting a nice rolling boil and leave it there. The wort does not need to be jumping out of the kettle

 

[peterj]

Yes water and wort will have slightly different boil off rates. The boiling point of wort will be slightly higher as well as the density, but it shouldn't really be that different. Not different enough to account for what you saw.

I would say having the lid 3/4 on is what did it. You had no lid with the water right? I never use my lid except when I'm letting things settle out before I transfer to the fermenter. Why did have the lid on?

 

[shtoive87]

FYI, the thread's from 2012...

 

[eltorrente]

FYI, the thread's from 2012...

Still a valid question.

I feel like it does make a difference, but have only anecdotal evidence. For instance, when I boil a starter, I always start with 2L and boil for 15 minutes, and my little pot will always boil down to around 1.55L or so (just under the 1.6 line). Every time I've done a higher gravity starter for a bigger beer, the level always ends up above 1.6L.

Same thing with boiling bigger beers in my kettle. A 1.055(ish) batch evaps at a rate of around 1.6 gallons per hour, and higher gravity (1.070 and above) seems to be in the 1.4 gallon range. I always use the same setting on my regulator to boil.

Of course, temperature and humidity play a big role, too - but it *seems* like it makes a difference to me. I'm sure there's an equation out there somewhere..

 

[peterj]

FYI, the thread's from 2012...

Ha! Wow definitely didn't notice that.