It's commonly accepted that it is best to brew with the boiler lid off (or at least with some method that extracts the steam). The reason for this is that some nasty things that we don't want in our brew are driven off during the boil. Presumably with the lid on, these condensate and then drip back into the boiler.
My question is, when is the critical time where these are produced - i.e. where do these nasties come from. My understanding is that they are obtained from the hops - is this right?
If they do come from the hops then presumably it is ok to have the boiler lid on loosely until the stage where the hops go in. For example, today I boiled for 30 minutes before adding the hops so presumably I could have had the lid on for the first 30 minutes?
My reason for being interested is that now the weather is colder, my 1.8kW Brupaks boiler struggles to maintain a vigorous boil. If I put the loose fitting lid on though it boils away madly even outside. Ideally I either need an additional element to kick it up a bit and maintain the vigorous boil with the lid off or else I need to insulate the outside of the boiler (perhaps both).
Any thoughts
