No boil in the boil kettle...

I've been wondering why it's necessary to "boil" in the boil kettle. By "boil" I mean adding enough heat to the wort to induce a phase change. We've all seen that there's a lag between the time we get to the (theoretical) boiling point and then a lag until the wort actually starts to boil. My question is: why boil?

I'm well aware of the hot break, DMS and hop isomerization (starting at 175-180°F range) associated with "boiling". What I'm not clear on what part of boiling is necessary?

When my (fictitious) friend in Leadville, CO brings his wort to a boil the temperature is only 193°F. When I boil my wort in Indianapolis the temperature is 210°F. Does my friend drive off any more or less DMS? Is his hop isomerization appreciably different? What about hot break?

Could one emulate the "boil" by:
- Bring boil kettle to 210 degrees.
- Pump purified air to bottom of kettle to emulate the boiling action

Would that drive off DMS in the same way a "real" boil would?

As I understand it, the precursor to DMS is converted to DMS with heat. The DMS is in turn "carried off" with the steam, so you need a good exchange of water at the surface of your wort, and a nice amount of steam leaving the kettle. The same reason you need a boil, is the same reason you can't leave the lid on the kettle during the boil. The DMS won't leave. It's not so much the temperatures that you and your 'friend' are boiling at, but the fact that you're sending DMS off into the air with the steam.

Hop isomerization is faster at 210 than at 193 ˚F (source: "The isomerization reaction was found to be first order, with reaction rate varying as a function of temperature"), but I don't know if it's an appreciable amount, especially at 60 minutes.

As for DMS, purified air would probably drive it off, but maybe not as well as steam. DMS is relatively polar, so I would assume the interaction with air would be a good deal weaker than with steam. Then again bubbling air through 210 ˚F water would probably hydrate it quite a bit and might be pretty close to steam.

Of course there are a couple reasons why we don't do this:
1. keeping a temperature static at 210 ˚F is not nearly as easy as keeping things at a boil
2. Purified air pumped through heat resistant tubing into a stone at the bottom of a kettle is not a trivially cheap investment

Still a really interesting thought experiment though!

From the Picobrew Zymatic website...

https://www.picobrew.com/About/FAQ.cshtml


The Zymatic® typically maintains a temperature just below boil. This near boil occurs in the heat exchanger, adjunct compartments and keg. Through testing we have found that there is nothing magical about boiling - it’s just traditional since beer was created a long time before thermometers and process controls. In a conventional homebrew system, boiling is important since the temperature control is not as precise - keeping the entire batch at 207° steadily for an hour is impossible for most home brew systems. Also in home brew systems, a vigorous boil ensures mixing of the wort. In the Zymatic®, this mixing is done by circulating the wort. We have run extensive testing for hops extraction, off flavors and clarity, and have found no detraction from having a “boil” temperature slightly less than boil.