Dan as a misunderstood genius. Or not.

Shoe on Jan-02-2007 at 10:03 PM RST @ 71.90.38.146

"Dan 'The ListerTroll'
Senior Member
Username: 'The ListerTroll'

Post Number: 3885
Registered: 03-2004
Posted From: 216.23.59.245

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Votes: 2 (Vote!)

Posted on Wednesday, January 03, 2007 - 12:21 am: Edit Post
Boilovers usually happen just before the boil starts. There is an insulating foam that forms over the wort. This foam superheats the wort and frequently causes a boilover. Once the boil starts to roll, the danger of boilover is usually past unless there is way too much power applied.

I use two elements of differing wattages. Both are powered to bring to a boil then one or the other is disconnected for the length of the boil.

Sizing the elements is the best way to prevent boilovers. Start out with a 3500W element. If this is insufficient, buy a larger one - they are cheap.

Dan
--This space is STILL being left intentionally blank.- "

Note that Dan refers to the foam as an insulating foam, and the wort as superheated. Frankly, I think he has a point there.

Liquids often boil with a few degrees of superheat (defined as the temperature the liquid is above its boiling point), because excess energy is required to overcome surface tension as a bubble begins to form in the liquid. This initial bubble formation, or "nucleation", can be eased by the presence of nucleation sites. Common examples are small cracks in coffee cups. Heat water in such a cup in the microwave, and you might witness significant boiling bubble formation only at the crack. Very clean containers with few nucleation sites are subject to "bumping", where a single massive bubble rapidly forms, throwing boiling liquid all over the place. That's why in chemistry lab you use a boiling stone in the bottom of a flask, the stone provides nucleation sites and reduces bumping.

Boiling over early in the boil may be a related phenonema. Until the hot break forms, nucleation sites are limited. As the foam forms, it covers the surface of the wort and insulates it, and less heat escapes. The wort superheats another degree or two, and significant bulk boiling occurs, leading to the boil over.