Lid on or off?

[MRMARTINSALES]

Hi,

I have a 100l stockpot that has a recessed rim for the lid to sit snug.

When I boil my wort I normally leave the lid slightly off centre meaning there is a 1cm or 2 gap to let steam out.

Do I need to leave the lid off completely during the boil to ensure dms is evaporated or will leaving a small gap ensure that it?s being evaporated off?

Please help.

[jomebrew]

DMS is part of it but you are trying to evaporate and condense the work along with the other miracles that happen during the boiling stage.  Anecdotal reports suggest you don't need to remove the lid but years of scientific research suggest it is prudent to prevent DMS.  With the list partially on, steam condenses on the lid and drops back into the wort feeding the potential off flavors back into the wort.

Or does it?  Since SMS is volitized into the steam, does it condense back to the same state when it drop back into the wort?  I believe it does and thus a negative feedback loop.

If you are adjusting the sparge water to account for less boil-off and are fine with a risk of DMS, then leaving the lid cracked is fine. 

[MRMARTINSALES]

Thanks.

I just have a feeling that my beer has high DMS content due to not having the lid off.

I recently visited a brewery and they have their boilers covered but with a chimney to outside to allow boil off.

So does this allow enough of a boil off for DMS to evaporate out?

Surely some liquid condenses on the cover around the chimney open and drops back in?

[jomebrew]

Brewery exhaust are designed with draw, fans and a condensation trap that keeps it from running back into the kettle.  At least the ones I've looked at. 

[brewfun]

I recently visited a brewery and they have their boilers covered but with a chimney to outside to allow boil off.

So does this allow enough of a boil off for DMS to evaporate out?

Surely some liquid condenses on the cover around the chimney open and drops back in?

Exactly what jomebrew said.

Steam stacks for brewhouses have features to aid evaporation. They are typically tall, which draws the moisture up quickly. They may also have misting nozzles in them or a fan to pull steam. Steam will want to go from the hottest to the coolest place as fast as it can.

To prevent condensate, most have a crook in the stack. This offset is below the point where the steam might condense and rain back down.The condensate then travels down the side of the stack and is collected in a ring just above the kettle. There's a drain for it that goes to the floor under the brewhouse.

Properly designed, steam won't escape through the kettle manway door. There will be an obvious vortex of air being pulled in.

If you collect this condensate in the first 20 minutes of the boil, it will have a distinctly canned corn flavor and smell. It diminishes as DMS is distilled out.