[oscarvan]

Intuitively I have been boiling gently. Just that little thermal in the center of the pot, no foam fest, just 212º.

Some people I read say they boil hard.....

Is there science to support one or the other?

[tygo]

You want it to be "rolling" so there are shapes forming on the surface to allow for the compounds you're trying to get rid of to vent off.  Other than that it depends on your system and the boil off you're trying to achieve.  I've been tweaking my boil lately to go with the gentlest boil that still gives me the roll to minimize the amount of wort I'm boiling off.

[Kaiser]

I suggest that you watch your boil-off rate. You want to be between 10 and 15% boil-off per hour. This is enough to strip undesirable volatile compounds (DMS is one of them), give you good wort movement for protein coagulation and the heating is gentle enough that you don't scorch the wort.

You can control the boil-off though the flow of propane. After a wile you'll get an eye for what a good boil looks like.

Oh look, post 1000 already. Wohoo.

Kai

[oscarvan]

Oh look, post 1000 already. Wohoo.

Kai

Congrabulations.....

[Thirsty_Monk]

You want to be between 10 and 15% boil-off per hour.

This is interesting number because commercial brewers are targeting 3% evaporation rate.
I read the Siebel document.

[tygo]

Yeah, I'm interested in hearing more about why 10-15% is the optimal range.  I've heard and read that before and has caused me to question my process since with my current equipment there's no way I'm getting in that range for a 5-6 gallon batch.

Expressing the optimal boil off rate as a % seems arbitrary.  Increasing the volume of the batch and therefore the boil, given the same equipment, is going to drop the %.  Does that really have an impact on the wort in some way?

I'm not surprised that commercial brewers are shooting for a much lower percentage given the volumes that they're working with.

[Kaiser]

You want to be between 10 and 15% boil-off per hour.

This is interesting number because commercial brewers are targeting 3% evaporation rate.
I read the Siebel document.

This is because they can.

The amount of water that is evaporated during the boil is directly proportional to the energy that is used for boiling. And ever since energy became a major cost factor in brewing brewing equipment manufacturers came up with ever more efficient kettle designs that allow the same level of DMS removal with ever lower boil-off rates.

Back in the 1970s they has so called "high power" kettles that could run evaporation rates in the upper teens.

There are only 2 out of the 5 "ations" of the boil for which evaporation is needed: volitiziation (sp?) and evaporation. The latter determines how much additional sparge water can be used and with that it is linked to the efficiency. One can actually calculate at what point the savings in grain equal the energy needed to boil off the excess water needed to get the malt savings from increased efficiency.

The more important one is the volitization part. The less you boil off the less DMS will be stripped from the wort. And since most of us have simple cylindrical kettles we can't use the evaporation numbers that a brewery with an internal cooker and possibly post whirlpool DMS stripping can run. Dr. Fix referred to a minimum of 8%/hr boil-off for sufficient DMS removal. I'll have to dig up other references that list such a number but I found that keeping the boil-off between 10 and 15% is a good compromise between making sure that DMS is sufficiently removed and that the wort is not boiled too hard or too much propane is used. I tried to push it down around 7% once and found that the resulting beer was a bit more sulfury than usual.

Tygo, the DMS stripping ability of the boil is actually tied to the boil-off rate and to the cooker design. As the wort size increased the boil-off will have to remain the same unless you also change the way the cooker is designed. Modern boil systems, like the Stromboli for example, spew out the wort as a large umbrella where there is much more surface area at which the DMS can escape.

Here are interesting PDFs on this subject:

* http://www.mbaa.com/Districts/Ontario/memoriesArchive/2008_01_25TechConf/pdfs/Brewhouse%20Optimization%20-%20Gattermeyer.pdf
* http://www.krones.com/downloads/wuerzekochung_e.pdf

Kai

[euge]

I boil it fairly hard and don't use the lid until flameout. No problems with DMS. Seems like I get a better break too.

[majorvices]

As long as the surface is turning over you are fine. You don't need to boil the crap out of it. I boil in a 55 gallon kettle and pretty much have the wort up a little higher than the 50 gallon mark and can achieve boil with minimum boil over. Once I have fought off the initial foam (a spray bottle or quick squirt with the hose works well for this) I can boil the rest of the brew-session without any further boil overs. The wort is definitely "rolling" and I always achieve good break and have no detectable DMS. My boil-off rate is a little bit less than 10% per hour, but I always boil for 90 minutes so that may be the difference maker.

[tygo]

Tygo, the DMS stripping ability of the boil is actually tied to the boil-off rate and to the cooker design. As the wort size increased the boil-off will have to remain the same unless you also change the way the cooker is designed. Modern boil systems, like the Stromboli for example, spew out the wort as a large umbrella where there is much more surface area at which the DMS can escape.

The boil off in gallons per hour would remain the same but the percentage would change as the volume increased, right?  Does the DMS stripping ability of the boil change if I'm boiling 8 gallons in a 15 gallon pot versus boiling 12 gallons in the same pot?

[tumarkin]

Tygo, the DMS stripping ability of the boil is actually tied to the boil-off rate and to the cooker design. As the wort size increased the boil-off will have to remain the same unless you also change the way the cooker is designed. Modern boil systems, like the Stromboli for example, spew out the wort as a large umbrella where there is much more surface area at which the DMS can escape.

The boil off in gallons per hour would remain the same but the percentage would change as the volume increased, right?  Does the DMS stripping ability of the boil change if I'm boiling 8 gallons in a 15 gallon pot versus boiling 12 gallons in the same pot?

if you've got your propane burner set the same, you'd boil more vigorously with 8 gals & less vigorously with 12 - with more stripping at the more vigorous 8 gal boil. if you're setting your boil visually to the same level of rolling than no difference (but you'd use up more propane). as with ingrediant cost, energy cost is (generally) of less concern to us homebrewers than it is to the commercial brewers.

[bonjour]

most brewpubs are exhausting the boil thru an opening about the size of a turkey fryer.  This has to limit evaporation rate.

[Mikey]

most brewpubs are exhausting the boil thru an opening about the size of a turkey fryer.  This has to limit evaporation rate.

Unless you are actually building a positive pressure or it's condensing in the flue and running back into the kettle, I don't see why it would.

[bonjour]

most brewpubs are exhausting the boil thru an opening about the size of a turkey fryer.  This has to limit evaporation rate.

Unless you are actually building a positive pressure or it's condensing in the flue and running back into the kettle, I don't see why it would.

Exactly,  I've never seen a heated lid and exhaust on a brew kettle to stop condensation.
I knew you knew your physics.

[tygo]

if you've got your propane burner set the same, you'd boil more vigorously with 8 gals & less vigorously with 12 - with more stripping at the more vigorous 8 gal boil. if you're setting your boil visually to the same level of rolling than no difference (but you'd use up more propane). as with ingrediant cost, energy cost is (generally) of less concern to us homebrewers than it is to the commercial brewers.

Right, I'm setting mine to boil visually to the same level no matter what the volume since I'm going for basically the least vigorous boil I'm comfortable with.