[tommymorris]

Do I care about boil off rate or boil intensity? I brew 3 gallon batches and my boil off rate is 12-15%. If I brewed larger batches the volume lost to boil per hour should remain constant, but, my boil off rate will drop. Doubling the batch size would half the boil off rate. My boil is a simmer.

Similar, question, if I put the lid on while boiling, I will loose less wort to boil off. But, really that wort will evaporate, condense, and drop back into the boil (right?). Didn’t adding the lid increase the boil intensity while lowering the boil off rate? Doesn’t this actually give a false sense of security since the boil intensity is actually higher in this case?

[Robert]

All else being equal, reduced evaporation will be an indicator of reduced thermal loading on the wort -- and THAT'S what you're really interested in.  Think of plotting a curve of time and temperature, you want to reduce the area under the curve.  By putting the lid on, I've reduced my evaporation rate.   But that's not just because of recondensing water, but because I can get vigorous circulation of the wort (for protein coagulation and hop utilization)  while applying less heat over less time; my burners are at about 2/3 of my bad old burn, and I've gone from 70 to 45 min.  The improvement in wort quality is undeniable, with full hop utilization and break coagulation.  If I took the lid off I'd evaporate more, but would also have to turn up the heat to get a roll going.  So you make a good distinction.  Evaporation rate is an indicator,  not an end.  Some breweries even get a dynamic boil by using a low pressure boiling vessel, thereby further reducing the heat required.

[mabrungard]

Vacuum boiling, pulsed boiling, boil cycling, external wort heaters, thin film, wort spreaders...there are a bunch of techniques that modern equipment manufacturers use in controlling wort heat stress and evaporation. They can all be useful, but its all for naught if you don't control the exchange between the kettle and the atmosphere. Covered boiling isn't a sin. However, there is a need for both covered and uncovered boiling in your boiling process.

I've gone to a 60 minute boil duration and 30 minutes of that is virtually entirely covered. That allows me to significantly reduce my heater setting. The wort is moving just enough to maintain a circulation. It isn't erupting. For the last 30 minutes, I uncover. Of course, that open kettle looses a lot of heat when uncovered, so the heater setting has to be increased. I also target a more strongly rolling wort boil...still not erupting.

Even when brewing almost 100% pils wort, I effectively reduce DMS to nearly unpercievable level. However, most beer styles that employ nearly 100% pil malt, often have an acceptable level of DMS stated in the BJCP guidelines. So having a bit of DMS in some brews, is OK. In beers made with the slightly darker pale malt, DMS is almost never a problem.

Most modern pro systems are targeting less than 10% evaporation loss in a 60 min boil. I have my system giving me about 8 to 10 percent loss. I've heard Bryan Rabe say that he's reduced his loss to around 6 percent, but he said the DMS perception was a little too prominent for his tastes. I believe he purposely targets a bit more evaporation (I think he said 8%) to avoid that problem.

The bottom line is that homebrew lore on wort boiling is about 40 years behind. We don't have to boil long and hard to produce good beer. There is a lot we can learn from the pro's on boiling.

[Robert]

As a tangent, boiling isn't even needed to eliminate DMS for the pros:  the Bud guys have long employed "wort stripping."  They boil enough to form DMS,  and the hot wort is then passed in a fine spray through a column with a counterflow of nitrogen, removing the DMS, on the way to the heat exchanger.   This is one way they've drastically reduced boil time.  For that matter, mechanical agitation can achieve protein coagulation, and hop acids isomerize above 180°F, sufficient to pasteurize wort.  So with the right equipment, it would be unnecessary to boil wort at all.

As to what practical applications we homebrewers can advance, I look forward to Martin's presentation.

[BrewBama]

Well, I don’t feel so bad with my ~10% boil off rate then. I still plan to try to reduce because I want more wort in the fermenter to allow for my losses there and still fill the keg.

The only other issue is trying to simultaneously increase the grain bill to account for the loss in OG at the reduced rate.


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[Robert]

Isn't it funny how many improvements to homebrew process end up with "if you dont mind just using a little extra grain?"  Yet another example of how we sometimes have an advantage over the bigs.