I was listening to a Brew Strong episode on head retention and John Palmer (IIRC) mentioned; words to the effect, that the high heat load of some propane jet burners can reduce head retention. I'm not completely clear on what he meant there but I took it to mean; "Don't boil the crap out of your wort." I've heard some say to boil really hard and don't recall ever hearing anybody (prior to this) say; "Don't boil too hard."
Anybody agree/disagree with this? Are there reasons to boil really hard or to ensure to NOT boil really hard (other than propane/energy usage)?
I don't have any real data but I have a couple of Pils-based beers that I boiled hard with a jet burner for 100 minutes. I started with ~8 gal wort pre-boil to reach a final volume of ~5.5 gal. The beers make foam but it drops very quickly. I know Denny often says bad head is due to bad fermentations, and I won't rule that out, but these beers are pretty clean and I pitched a lot of yeast (cold), used yeast nutrient, aerated well, yada, yada.
This is using a relatively new brew stand with jet burners, perhaps I was puttin' the spurs to it just because I could. FWIW, last weekend's batch of ESB that I boiled gently for only 50 minutes? I couldn't read the hydro sample for an entire hour because the foam wouldn't subside (I'm not exaggerating, a full hour!). But it was clear as a bell (as usual).