FromZwolle said:

i usually keep mine to just barely boiling. the only real difference that i've encountered is the boil off volume.

so what is just barely boiling?

my kettle is large, so for me, i like to keep it where maybe every 3-5 seconds, a large bubble breaks the surface, but for the most part, the surface is flat and you can see the liquid moving beneath.

Too hard a boil is bad ..... thermal loading ..... bring it to a good boil until it settles down, then turn down the heat to what is described above ..... that's my my motto

BenS said:

A stronger boil is suggested.

Proof: http://bavarianbrewerytech.com/news/boilhops.htm

i read it, but i'm not convinced. a 3-5 degree difference shouldn't matter for any of the reasons they listed.

also, the point about driving out the oxygen is silly.

boiling hard enough to drive off 5% is easily achieved with a violent boil.

Thermal loading and a fast chill together is the devil!

Water also does not go above its boiling temperature. It simply becomes vapor. Which can be much hotter.

That is why wort boils so crazy hard ... with huge big bubbles .... the water turns to vapor like mad since the suspended material is hotter than the water ...

This is more important for bigger beers .... not so much for bud light clones ....

A 10 per cent solution of sugar is one that contains 10 grams of sugar and 90 grams of water or one having these proportions.

Read more: http://chestofbooks.com/food/science/Experimental-Cookery/The-Boiling-Point-Of-Water-And-Solutions.html#.UStzH6XCaSo#ixzz2LvA5U8QV

Let's assume that 10% of the weight of the wort is solubles that have come from the mash, which I think is realistic. Of course it could be lower or higher depending on the beer being produced. I also realize that we aren't pulling straight sucrose from the mash but it puts us in the ballpark.

The above listed website has a chart that shows that a 10% sugar(by weight)/water solution has a boiling temp of 100.4C, 20% sugar/water = 100.6C. Not much difference from water.

None of that explains the idea of thermal loading. From the same website above,

If a thermometer is held in the liquid it is found that when this point is reached the temperature is constant. This is the boiling point. A child might say that when a liquid is bubbling it is boiling, and it would be a fairly good definition. However, the chemist or physicist would word his definition differently. With vapor formation, pressure is exerted. Since the bubble is less dense than the liquid it comes to the surface. But the bubble cannot reach the surface until the pressure within it is just a little greater than the pressure of the liquid on the bubble. The pressure on the bubble in an open pan comes from the weight of the column of liquid above it and the atmospheric pressure on the surface of the liquid. Another way to define the boiling point is to say that it is the temperature at which the pressure of the saturated vapor within the liquid is just greater than the outside pressure on the surface of the liquid.

Read more: http://chestofbooks.com/food/science/Experimental-Cookery/The-Boiling-Point-Of-Water-And-Solutions.html#.UStzH6XCaSo#ixzz2LvCyP1sl

frydogbrews said:

i read it, but i'm not convinced. a 3-5 degree difference shouldn't matter for any of the reasons they listed.

also, the point about driving out the oxygen is silly.

boiling hard enough to drive off 5% is easily achieved with a violent boil.

The temperature difference between a simmering pot of wort and a 'violently boiling' pot of wort is not 3-5F, it is very minimal.

Boiling water does drive out oxygen, I don't know the exact reason why it's important for brewing, but there's no argument that boiling does reduce the % of oxygen dissolved in water. Of course, lots of oxygen is also re-absorbed into the water when cooled.......

A 5% evaporation rate is easily achieved

mors said:

The only real reason for a rolling boil is to drive off DMS and to further evaporate water if that is your desire. A low boil you will drive off less DMS.

You actually drive off less DMS if the boil is too strong .... this is why the Belgians "simmer" their wort. I noticed a huge difference in my beer after I read "brew like a monk" and stopped boiling the hell out of my wort.

I know what I am saying flys in the face of what most modern brewing convention insists .... but the Trappists have been saying this for a very long time ... and my experience bears them out ...

ceannt said:

There is a lot more in wort besides sugars too .... proteins.... particles of grain ... hops and such. If it takes 50,000 BTUs to maintain the temp necessary to boil the water .... and you run the burner at 100,000.... all those BTUs have to go somewhere(2) .... most dissipates out the side of the pot .... but enough loads up in break material and other solids to form a constant "bubble" of water vapor around the particles(3) ... keeping the DMS from going into suspension in the water and being driven off .... only a single degree above boiling(1) will cause the water around each particle to immediately become vapor. At least this is my theory ....

(1) there is no such thing as 1 degree above boiling, see previous posts
(2) The amount of BTU's varies by mass(The volume of water).
Those BTU's do go somewhere, into the liquid. Increasing the energy going into the boil increases the energy being boiled off, hence a more vigorous boil. It does not stay in the liquid.
(3) If a solid is immersed in a boiling liquid, that solid will establish equilibrium with that liquid. Hence, nothing in a boiling pot of water/wort/whatever, will ever be a higher temp than the liquid.

"Those BTU's do go somewhere, into the liquid"

and that.... is thermal loading...

My explanation may not be very scientific.... but almost thirty years of brewing has proven to me that my beer is a whole lot better boiling the way I do...... "empirical evidence"

ceannt said:

Tell you what..... mash 15.5 pounds of Pilsner malt.... and nothing else... split the wort.
Boil the hammered hell out of half of it for 60-minutes (add an ounce of noble hops for bittering only) and then immediately chill at flame out. Call this number 1.
Take the other half and bring it a boil, soon as it stopped foaming up lower the heat and keep it right "on the hairy edge" of boiling for 90 minutes (add the same quantity of hops at 60-min.) and let it sit for 5 or ten minutes before you chill, call this number 2. Pitch the same variety and quantity of yeast in both samples, and ferment side by side... I will qurantee you that you will like sample number 2 a whole lot better... and that sample one will reek of DMS.

I may be right, but it's not because of 'thermal loading'. There is no such thing, not in the way you are describing. 'Thermal loading' of water occurs below boiling temperature as the liquid gets hotter, water molecules are no longer able to absorb any more heat/energy at boiling temp. Hence, the undergo a phase change into vapor.

I am not disagreeing with you that a simmering pot of wort can make beer that is as good or better than a vigorous boil, I simply do not know. I will defer that to your brewing experience. I just know that it is not because of the physical/boiling properties of water. More likely it has to do with the chemical properties of the malt, but I don't really know.

BenS said:

ceannt said:

Tell you what..... mash 15.5 pounds of Pilsner malt.... and nothing else... split the wort.
Boil the hammered hell out of half of it for 60-minutes (add an ounce of noble hops for bittering only) and then immediately chill at flame out. Call this number 1.
Take the other half and bring it a boil, soon as it stopped foaming up lower the heat and keep it right "on the hairy edge" of boiling for 90 minutes (add the same quantity of hops at 60-min.) and let it sit for 5 or ten minutes before you chill, call this number 2. Pitch the same variety and quantity of yeast in both samples, and ferment side by side... I will qurantee you that you will like sample number 2 a whole lot better... and that sample one will reek of DMS.

I may be right, but it's not because of 'thermal loading'. There is no such thing, not in the way you are describing. 'Thermal loading' of water occurs below boiling temperature as the liquid gets hotter, water molecules are no longer able to absorb any more heat/energy at boiling temp. Hence, the undergo a phase change into vapor.

I am not disagreeing with you that a simmering pot of wort can make beer that is as good or better than a vigorous boil, I simply do not know. I will defer that to your brewing experience. I just know that it is not because of the physical/boiling properties of water. More likely it has to do with the chemical properties of the malt, but I don't really know.

I don't know either... at least on a scientificaly based "fact"..... but boiling like this was probably my biggest "breakthrough" in brewing better beers since I stopped racking to secondary back in the late 80's... (back when conventional "wisdom" said that anything longer than a week in Primary would ruin the beer...)
I used to avoid Pilsner Malt like the plauge because every dang time I used it... I ended up with DMS.... One day I decided to brew a Belgian, and my research led me to the low boil... I found that it made all of my beers better... significantly...

I truly think that most of the reason the "big boys" say to boil hard... is that it is easy... it's a pain in the backside to get the boil "just right" and takes a lot of attention and constant adjustment... I'm not sure its even possible to do with an automated system... too much judgement involved... its more "feel" than anything... (if that makes any sense at all)

My theory that the particles are not suspended in water, but in vapor may have no merit at all.... but I do see the particles rise to the top, when gravity should be forcing them to the bottom... I would think that that is because they are suspended in vapor... maybe even at a molecular level... I don't "know" this from textbook science... but I do know that the DMS issues I had when I boiled the crap out of my wort went away when I started doing it like this.... and all my beers were smoother, and had better flavor.

frydogbrews said:

so there is your one degree over boiling.

To Ben's point earlier.... There is no such thing as one degree over boiling. If you change the chemical makeup of the liquid you are boiling then 213 is the new boiling point. One degree over boiling results in a gaseous state.


And yes, out of all this THAT is the point I chose to make. I'm really just enjoying the read on the rest of it.

@bens Wort is not a pure solution, its also a suspension, with great quantity of insoluble solids in it.

The things that can get over the solution boiling point are those insoluble solids, they represent a substantial thermal mass and are what can break down and release undesirable flavors if heated too much.