Boil Evaporation Rates: Lid on or off?

[hirns]

At present I have about next to no evaporation loss during boils as I use a stainless pot with a clear glass lid through which I keep an eye on things. I give it a stir around the edges to add the hop scum back in every 10 minutes or so, but the lid is on for most. I mash with 2.3l of water/kilo of grain, recycle the first runnings drain and then stir the mash add enough water to make up the 23 litre batch + an extra litre or two for mashtun deadspace and cold break in the pot and repeat the process. I see recipies which start with 26+ litres and end up with 23l after evaporation.

Is what I'm doing okay-I thought that I would be trapping more of the hop flavour and aroma. My SG's have been close to the mark so I don't think that I need to concentrate the boil at all. For most I've followed the advice of people on this forum, but can't recall reading anything in relation to lidded/unlidded boils. Wanted to check my process and make sure I'm not meant to be letting some nasty compond evaporate .

Hirns

[Finnagann]

I do believe there are some nasty volatiles that come out of the hops when boiled. Keeping the lid on keeps them in your beer

I only use my lid when I'm bringing things to a boil then it becomes a sanitised surface to set things on

[warra48]

Definitely do your boil with the lid off for AG and partial brews.

Wort has sulphur compounds that evolve and boil off.
If they aren't removed during the boil, they will later form dimethyl sulphide, which contributes a cooked cabbage or cornlike flavour to the beer.

With the lid on, these compounds drop back into your beer, potentially creating problems for you, and having these show up in your beer.

If you boil off too much, you can add extra water to restore your volume in the last 10 minutes or so of the boil.

The reason for hop additions from about 20 minutes to flameout is to retain hop flavour and aromas. The shorter boil time for those prevents them being boiled off.

[hirns]

Thanks guys: That sounds like one easy inprovement for me . What about the hop scum that foams up around the edges of the pot that I periodically scrape back in? Is this necessary? Thanks in advance for responses.

Hirns

[Tipsy]

What about the hop scum that foams up around the edges of the pot that I periodically scrape back in? Is this necessary?

I skim the scum from the malt and get rid of it.
The hops that climb up the side of the pot I scrape back in.

[hirns]

Thanks, was doing that with the hot break, dammed if I've ever read anything about this lid thing. Oh well live and learn!

Hirns

[Trough Lolly]

Lid off is the go - especially when you want to drive out the DMS from lager malts.

Cheers,
TL