My 10 gallon brew pot is more on the short and squat side. I am wondering if I could leave the lid on half way to prevent excessive evaporation. Would I have DMS issues if the pot is halfway covered?
You very well could have a DMS problem by leaving the lid on halfway. I would try to adjust volume accordingly. Start with more than expected and boil longer if necessary.
Dave
You’ll be fine leaving your kettle partially covered as long as there’s enough of an opening for steam to escape. The ROT is to leave at least 15% of the kettle uncovered.
I leave my lid partially on for the same reason. Plus I find that I can keep the same rolling boil with less heat. Win/Win. When the chiller goes in the last 15 minutes I do take the lid off completely and increase the boil a little. I can’t tell you if it matters or not but it works for me. YMMV. Cheers!!!
If you think DMS will be an issue leaving the lid on partially take a look at almost every commercial system and see how it is entirely covered except for the part where the chimney is.
Leaving the lid partially on may not be enough on its own to minimize evaporation. I routinely leave the lid partially on my kettle to help reach and maintain a boil with larger volumes on my stovetop. I find that I actually get more boiloff with the lid partway on than fully off. I assume that this is because I can maintain a more vigorous boil. You will likely have to ease off on the throttle on your burner in conjunction with leaving the lid partially on to see a significant reduction in your evaporation rate.
I’m lid averse after having some DMS problems in a Kolsch. However, I was boiling for 60 minutes and switched to 90 minute boils. Floor malted BoPils. Do you think it’s the same as above with this as well?
I just tried the Floor malted BoPils for the first time. 90 minute boil (and not a super strong one, either), lid 2/3 on, and no DMS that I can detect.
Good to know. I like Denny’s 15% Rot too. May have to consider this…
Dave
What is ROT? Sorry, I’m new to all of this.
Rule of Thumb - either that or Denny is using a wooden lid!
Gotcha. I just brewed Friday night and we did put the lid on during the boil, leaving it partially off to the side. It was in the garage and the wind was kicking up quite a bit making the temperature drop rather quickly. Hope it didn’t create any DMS in our brew.
FWIW, ROT was a new one for me too. LOL ROTFL RDWHAHB 
+1. AFAIC anyway.
Not that I’m any good with these acronyms, but I think it is “AFAIK” - FWIW. Very funny stuff, though, guys.
The DMS can get out as long as it is vented to a reasonable degree, so RDWHAHB or whatever you have available. Still chuckling…
FWIW - I meant “As far as I’m concerned”, hence AFAIC. LOL, RDWHAHB !
AFLAC!!!
Gotcha - I stand corrected (ISC).
They also have kettles designed to keep condensation from dripping back into the boil.