Boil-off rate calculator

[Alex Helbig]

HI All. I was wondering if anyone knows of a boil off rate calculator that takes ambient temperature and humidity into account?

I've been using BeerSmith for quite a few years now to calculate water volumes and it has generally had me in the right zone. Two weeks ago I had an usually high rate of boil-off in a 60 minute boil - volume reduced from 28.5 down to 25L. Normally I would boil off about half of that volume. After cooling shrinkage I ended up with a much smaller batch than expected which messed up my numbers. I decided to top up with some boiled water to hit my target volume and gravity. It was a fairly typical Queensland winter day - dry and about 20°C; humidity might have been about 20%.

Before I kick off my next brew, I was thinking that I should adjust my volumes based on temperature and humidly. Is that worthwhile, or a waste of time?

Cheers
Ejek.

 

[golfandbrew]

It's okay to have to make adjustments on the fly. I would rather have to dilute to reach a lower gravity than boil longer than planned to hit a higher one.

 

[punkrocker1991]

Am interested to hear experiences around this, as I've also found variable boil-off, where 18-19L pre-boil (hot) can lose between 2.8-3.5 L/hour. I'm sure there's maths around humidity, ambient temperature, and air flow, as well as volume of wort and volume of boiling vessel coming into play.

 

[djebel]

My only experience was due to stupidity. Did a stovetop BIAB at a mate's place, boiling away but volume wouldn't reduce. Eventually noticed condensation running down the wall some distance away .

Opened a couple of windows and suddenly the volume started reducing. The beer wasn't very good, but did have some nice caramel/toffee flavours from the extended boil time.

 

[wide eyed and legless]

HI All. I was wondering if anyone knows of a boil off rate calculator that takes ambient temperature and humidity into account?

I've been using BeerSmith for quite a few years now to calculate water volumes and it has generally had me in the right zone. Two weeks ago I had an usually high rate of boil-off in a 60 minute boil - volume reduced from 28.5 down to 25L. Normally I would boil off about half of that volume. After cooling shrinkage I ended up with a much smaller batch than expected which messed up my numbers. I decided to top up with some boiled water to hit my target volume and gravity. It was a fairly typical Queensland winter day - dry and about 20°C; humidity might have been about 20%.

Before I kick off my next brew, I was thinking that I should adjust my volumes based on temperature and humidly. Is that worthwhile, or a waste of time?

Cheers
Ejek.

If you take notice of what Charlie Bamforth and other pro brewers suggest is boil like you mean it. A good vigorous boil, not a simpering simmer.
Best way to calculate is put a specified amount in the boiler boil for a set time and do the calculations from there, if its 10 litres boiled hard for 30 minutes calculate what that would be on a 28.5 litre for 60 mins. I have read about humidity and the effect but for a small quantity of beer I wouldn't be worrying about it.

 

[Brewmerang]

I have found that the most significant change in boil off is due to heating differences. The temperature of the wort cannot exceed its boiling temp.
By applying more heat, you affect a more vigorous boil. This is an obvious indication that the temp is being limited by an increased release of water vapour.
I am led to believe that boil should be as vigorous as possible, but not so harsh as to cause scorching at the point where the heat is applied.

If you maintain this consistent heat balance, then:
As ambient humidity rises, the boil appears more violent in order to release the same volume of water vapour to regulate the temperature.
As ambient temperature rises, the boil appears more violent in order to release a greater volume of water vapour to regulate the temperature.

Just my observations and reasoning, of course, I could be wrong

 

[Brewmerang]

I found this interesting comment on reddit, posted by 'UnoriginalUse' 3 years ago:


"What I usually do to determine variable boiloff rate is a gravity * volume calculation. If I start the boil with 16L of 1060 wort, and I'm aiming for a 12L 1080 wort, I take a second gravity reading around 10 minutes into the boil. If I get a 1063 gravity, I know that I boiled off 0,76L in 10 minutes, and I can determine that the volume will be at 12L after another 42 minutes; I can also determine how much water I'd need to add to be able to do a 60 minute boil if my hop schedule requires it."