Biere De Garde super long boil time

[nickharbour]

I'm looking into brewing up a Biere De Garde and I'm curious about trying out the technique of extended boil times to achieve the kettle caramelization for color and flavor. The book (farmhouse ales) says some breweries boil hard for 3 hours or more (one example cited 12 hours). It does not give specific technical advice for how to conduct the boil though, and that is where my questions come in.

My concern is that by continually topping off the water in the kettle I'll effectively be concentrating the minerals in the water, resulting in a metallic or otherwise incorrect flavor. I have considered covering the boil during most of the time then uncovering it for the final 90 minutes. I hesitate to do that though as with a hard boil I feel it may be hard to contain the boil overs. Does anyone who has tried extended boil times have any advice?

 

[dawgmatic]

If youre worried about concentrating your waters mineral content then top off with distilled water from the store,

 

[ghack]

Take the first gallon or two of your first runnings and boil it down to a pint to a quart. Use a big pot and keep an eye on it; it will foam up massively (a quart will fill a 5-gallon pot). Stir it when it gets too big. As it boils down you will need to stir more and more often. You'll see the color start to change. By the end you will need to stir constantly and it will have significantly darkened. Add it back to your main wort, and top off as required.

A lot less time and produces pretty good results IMHO.

 

[TNGabe]

I like to do long boils (3 to 4+ hrs) for my biere de garde and flanders style ales. General consensus is that there is no reason for an extended boil, but I think it's fun so it's what I do. Haven't experienced excess mineral buildup, but my water is fairly soft.