[ynotbrusum]

Not so sure on this one, guys.  At what boil rate are you ridding Pils malt of its SMM?  I tend to push the pilsners pretty hard for at least a goodly portion of a 90 minute boil.  No science behind this, just what I had always heard and the results have been favorable.  I guess it's time to call the Brulosopher....

[hopfenundmalz]

Commercial brewers have a pretty vigorous boils from the ones I have seen. The 100 bbl system at Sierra Nevada Chico looked like the volcano. The boil off rate is down around 5% as they have a small stack for the vapors to escape.

[rob_f]

I wish we could get rid of the concept of percentage boil-off.  It makes no sense. Consider 5 gallons of wort boiling at 1 gal/hr:

Hour  vol   %/hr
  1       4   20
  2       3   25
  3       2   33
  4       1   50
  5       0   100

A fixed rate of fuel supplied boils off a fixed amount, not a percentage.

[mabrungard]

I agree with you, Rob. If the wort surface area in the kettle is constant with respect to depth, then the boil off rate is likely to be constant too. My observations are that it is a constant rate in my system. 

[S. cerevisiae]

I'm wondering if I shouldn't just check the temp. of the boil vs. looking at the actual boil to gauge where I am. My point being that if I'm at 212 then it's boiling technically.

The problem with that strategy is that water is vaporized into steam 100C at standard atmospheric pressure; hence, the temperature does not rise as the boil rate is increased.  The extra heat energy is carried away with the vapor (see Latent Heat of Vaporization).  This physical phenomenon is the reason why we have to heat water under pressure in order to increase that temperature at which it converts into steam.  The weight that is used on a pressure cooker/canner raises the internal pressure of the cooker 15 lbs above atmospheric pressure.  If the external pressure is standard atmospheric pressure, water will not boil until the internal temperature reaches 121C (251F).

[HoosierBrew]

A fixed rate of fuel supplied boils off a fixed amount, not a percentage.

+1

[coolman26]

My BK is tall and narrow.  My boil off is 1.3 gal/hr.  I have found this is where my boil off is consistent.  I've found that if I try to turn the rate down, it changes my break.  I don't think there is a correct amount.  As long as you know what it is for your system, that is what is important.  All about repeatability right?

[a10t2]

The 100 bbl system at Sierra Nevada Chico looked like the volcano. The boil off rate is down around 5% as they have a small stack for the vapors to escape.

I would assume they have an internal calandria, which is why it looks so vigorous relative to the boiloff rate.

I wish we could get rid of the concept of percentage boil-off.

Agreed, but when there are four orders of magnitude difference in volume between the largest and smallest brew systems, it's just something you have to put up with.

[denny]

Like efficiency, I think this is a spot where it is easy to get stuck chasing the dragon. Do what works for you and makes you good beer. I am confident that I have as little boil off as possible in my current environment with my current kettle and burner. I'm happy, beer is good, I'm moving on.

Percentages of boil off are absolutely useless here, IMO. Geometry, temperature, wind, and humidity all play a role. Plus when I brew 5 gallons, the boil off is the same as when I brew 10 gallons.

^^ All of this.  I'm pretty sure I make good beer boiling off 1.2 gal/hr. If you were 1.8+/hr, it might be time to dial the burner back.

+i've not seen any conclusive data that 1 gal per hr boil is better than 1.5 gal/hr boil beer.

Absolutely agree with you guys.  If higher boiloff negatively affects the beer, I've been making crappy beer for 17 years.  Someone alert the judges!

[HoosierBrew]

Like efficiency, I think this is a spot where it is easy to get stuck chasing the dragon. Do what works for you and makes you good beer. I am confident that I have as little boil off as possible in my current environment with my current kettle and burner. I'm happy, beer is good, I'm moving on.

Percentages of boil off are absolutely useless here, IMO. Geometry, temperature, wind, and humidity all play a role. Plus when I brew 5 gallons, the boil off is the same as when I brew 10 gallons.

^^ All of this.  I'm pretty sure I make good beer boiling off 1.2 gal/hr. If you were 1.8+/hr, it might be time to dial the burner back.

+i've not seen any conclusive data that 1 gal per hr boil is better than 1.5 gal/hr boil beer.

Absolutely agree with you guys.  If higher boiloff negatively affects the beer, I've been making crappy beer for 17 years.  Someone alert the judges!

[tommymorris]

Most home brewers boil too rapidly.  I do not know where the "rolling boiling" thing originated in home brewing.  However, the boil only needs to strong enough to disturb the surface, which another forum member described as a "hard simmer."  Losing more than 15% per hour to evaporation has a negative effect on beer stability and quality.  I did not realize the difference a lower evaporation rate made until I started to use an induction range that was incapable of producing a hard boil.  The maximum amount of evaporation that should occur with 6.5 gallons in an hour is 0.975 gallons.  Ideally, the evaporation rate should be 0.65 gallons per hour.

What is lost from a quality perspective from a strong boil? Same question related to stability?

[markpotts]

I also think that boil off in terms of % doesn't work.
My batches are either 25, 40 or 50 litres (sorry I'm in the UK ) and the amount lost to boil off (in terms of volume) is the same in each case; regardless of batch size.
It took me a while to figure this out.....I usually make 40 litres and at first couldn't understand why my numbers didn't work out when making a smaller or larger batch.
The best thing to do IMO is measure the boil off per hour and then apply this figure to your recipes and adjust accordingly if you boil for longer than 60 mins.

[S. cerevisiae]

What is lost from a quality perspective from a strong boil? Same question related to stability?

What noticed almost immediately after I started to use an induction range that was incapable of producing a strong rolling boil was that my beer had better foam.  The second thing that I noticed was that the beer stayed fresher tasting longer.  Most of my beers are 4 or 5 months old by the time that they have been completely consumed because I only a drink two to three pints on a good week.