Covering the brew pot during boil

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wheatgerm

wheatgerm

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I'm doing my first ever brew next weekend and I'm trying to get all my ducks in a row.

I'm doing an AG brew and have read most everyone say that you need to compensate for boil off by shooting for starting the boil with 6 to 6.5 gallons of wort in order to get around 5 gallons by the end of the boil. Couldn't that be cured by simply covering the brew pot during boiling, or is that a no-no for some reason? Thanks!
 
You want to leave the brew pot uncovered in order to allow dimethyl sulfides ("DMS") to boil off. DMS will cause a "vegatable" off-flavor in your beer in high quantities. Different malts have different levels of DMS. For example, recipes with pilsner malt often call for a 90 minute boil (with no lid) in order to facilitate the removal of DMS.

EDIT - Just a point of clarification since this is in the beginners forum: DMS is only an issue with all-grain brewing. However, when brewing extract, I would still leave the pot uncovered in order to keep boil-overs at bay.

Also, Welcome to HBT :tank:

EDIT #2 - It's OK to leave the lid on while you get up to a boil in order to save some time. Once you start your timer for the boil, then you should take the lid off.
 
The only problem I could imagine would be that during the boil you're driving off certain undesirable compounds like dimethylsulfide (sp?). I'm not sure if covering the boil would cause a problem with this or not. I'm sure an expert will weigh in shortly.
 
covering the pot can lead to off flavors (cooked veggies/cabbage) because some sulphur compounds (called DMS) get trapped in the kettle instead of evaporating while you boil.
 
Thanks guys. After reading your responses it jogged my memory of this in Palmer:

"DMS is continuously produced in the wort while it is hot and is usually removed by vaporization during the boil. If the wort is cooled slowly these compounds will not be removed from the wort and will dissolve back in. Thus it is important to not completely cover the brewpot during the boil or allow condensate to drip back into the pot from the lid. The wort should also be cooled quickly after the boil, either by immersing in an ice bath or using a wort chiller."

http://www.howtobrew.com/section4/chapter21-2.html

So much to learn.
 
look at the bright side... you learned by asking and reading, rather than making 5 gallons of cabbage flavored beer.

Though, one could argue that if you HAD made the cabbage beer, you most definitely would not ever forget what caused it and how to avoid it.
 
Walker said:
look at the bright side... you learned by asking and reading, rather than making 5 gallons of cabbage flavored beer.

Though, one could argue that if you HAD made the cabbage beer, you most definitely would not ever forget what caused it and how to avoid it.
Click to expand...

Either that or he'd make cabbage beer again for St. Paddy's day! You could even "dry-hop" with a slice of corned beef to make it authentic!! :D

Seriously though, it was a good question!
 
wheatgerm said:
I'm doing an AG brew and have read most everyone say that you need to compensate for boil off by shooting for starting the boil with 6 to 6.5 gallons of wort in order to get around 5 gallons by the end of the boil.
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Yeah that is about what I end up with however the amount of boil off is also determined by the size of the kettle and the length of the boil.

My kettle is about 17" in diameter and I do ~90 minute boils, I start with about 7 gallons and end up with ~5.5. You could always add a litte water to reach post boil volume too but different temperature/density liquids don't mix together easily.

I always start my boil with the lid on(watching constantly for boilovers) then keep the lid off for the rest of the time.

Welcome to the wonderful obsession of homebrewing and good luck!:mug:
 
When your doing an all grain, you want to use extra water, because this will help extract more sugars from the grains. If you use an extra 1-1.5 gallons of sparge water you will improve your effectively, assuming everything else is the same. That said, you don't want to over sparge either.

Losing water isn't really a problem. You can always top off with tap water before pitching if you lose too much. btw, I always top off because I don't have a big enough pot to to a full boil.
 
Oh.. that sucks. I covered my pot after I soaked my grains, and after I added the malt extract but not once I put the hops in..... so it was maybe covered for 30 minutes. but then uncovered for an hour or so. Need to get a stronger burner (That is why i covered it...).
 
Along with the previous reason, I just want to throw in that the one time I covered a pot for a little bit a ton of the hop pellets rose up and got stuck to the inside of the lid. Didn't ruin anything, but if you covered it and didn't know they got stuck that would completely throw off your hop profile.
 
pjcampbell said:
Oh.. that sucks. I covered my pot after I soaked my grains, and after I added the malt extract but not once I put the hops in..... so it was maybe covered for 30 minutes. but then uncovered for an hour or so. Need to get a stronger burner (That is why i covered it...).
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You should be fine!

It is OK to keep your kettle covered while bringing it to a boil. In fact it is a good idea cause it saves energy and speeds up the process you just have to really watch your kettle for potential boilovers.

Once your wort is boiling then you want to keep it uncovered, or if on a stovetop, keep the lid on enough to keep a strong boil but still lets a lot of steam escape!
 
KevinW said:
Yeah that is about what I end up with however the amount of boil off is also determined by the size of the kettle and the length of the boil.
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As well as kettle dimensions. Two 8 gallon pots will have different evaporation rates if one is short and wide and the other is tall and narrow. Less surface area gives you a slower evaporation rate. That's why chefs will use a wider pot if they want their sauces to reduce and a taller one if they want to avoid it.
 
pjcampbell said:
Oh.. that sucks. I covered my pot after I soaked my grains, and after I added the malt extract but not once I put the hops in..... so it was maybe covered for 30 minutes. but then uncovered for an hour or so. Need to get a stronger burner...
Click to expand...


This is mainly an issue for all grain brewing. Your beer's fine.

Here's how it works. When your wort is at high temperatures, it starts producing DMS, but since it's boiling (with the lid off) the DMS is being cooked away. So as long as you boil it for a good hour with the lid off and you cool it quickly, your fine. (you may need 90 minutes for light beers).
 
ChshreCat said:
As well as kettle dimensions. Two 8 gallon pots will have different evaporation rates if one is short and wide and the other is tall and narrow. Less surface area gives you a slower evaporation rate.
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Sorry, I don't believe that is completely accurate. You are correct regarding evaporation, but that isn't the same as boiling.

For each 970 BTU you get into the wort, 1 pound of water ( ~ 1/8 gallon) will turn to steam and get out of the pot. Doesn't matter what shape the pot is.

Of course, some shapes are better for gaining the maximum heat from a burner. That is where the difference lies.

For electric brewers (me), the boil-off rate would be identical if I boiled in an Erlenmeyer flask or a pie pan.
 
I think the free surface area will make a difference to the amount of water lost during the boil. While the wort is boiling, it is also evaporating from the open wort surface. Passedpawn is correct about the heat required to boil off a pound of water, but evaporation from the hot wort surface takes place as well. A larger surface area will evaporate more than a smaller surface area, so pot dimensions will make a difference.

Think about it from a different point of view - heat some water or wort to 200 degrees, it won't boil but it will evaporate. It will evaporate faster from a pan than from an ehrlenmeyer flask. Bringing it to a boil will not change the relative evaporation rates of the two containers.

The boiling process will release more water vapor than the evaporation process, but the two add up to the total "boil off rate".
 
AiredAle said:
I think the free surface area will make a difference to the amount of water lost during the boil. While the wort is boiling, it is also evaporating from the open wort surface. Passedpawn is correct about the heat required to boil off a pound of water, but evaporation from the hot wort surface takes place as well. A larger surface area will evaporate more than a smaller surface area, so pot dimensions will make a difference.

Think about it from a different point of view - heat some water or wort to 200 degrees, it won't boil but it will evaporate. It will evaporate faster from a pan than from an ehrlenmeyer flask. Bringing it to a boil will not change the relative evaporation rates of the two containers.

The boiling process will release more water vapor than the evaporation process, but the two add up to the total "boil off rate".
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So, you are saying water evaporates. I'll buy that. I'd say it is insignificant compared to the boiloff. And, given this assertion that evaporation is insignificant, I'll stand by my prior statement that the shape of the pot does not have any significant effect on the boiloff rate.
 
Welcome to the wonderful obsession of homebrewing and good luck!
Click to expand...

Thanks much. I have my brew day schedule written out step by step, so I'm hoping it will go smoothly.

The boiling process will release more water vapor than the evaporation process, but the two add up to the total "boil off rate".
Click to expand...

I would think that the evaporation rate would be diminished by the saturated air directly around the surface of boiling water, so that only the loss from steam would become a factor. I guess there's one way to find out. Put equal amounts of water in a wide stainless skillet and a narrow pyrex flask and boil them both for 30 minutes then measure how much is left in each.
 
passedpawn said:
So, you are saying water evaporates. I'll buy that. I'd say it is insignificant compared to the boiloff. And, given this assertion that evaporation is insignificant, I'll stand by my prior statement that the shape of the pot does not have any significant effect on the boiloff rate.
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i took chem a while ago but as i recall the larger surface area allows the vapor pressure to alleviate faster than a more narrow one. the less vapor pressure there is the easier the liquid boils. this is why when you blow on a boiling pot the foam goes away you are decreasing vapor pressure. or something along those lines.
 
I would think that the evaporation rate would be diminished by the saturated air directly around the surface of boiling water, so that only the loss from steam would become a factor. I guess there's one way to find out. Put equal amounts of water in a wide stainless skillet and a narrow pyrex flask and boil them both for 30 minutes then measure how much is left in each.
Click to expand...

well you would need to have similar vessels to boil in since those two would give you different amounts of heat escape and retention.
 
Tinga said:
well you would need to have similar vessels to boil in since those two would give you different amounts of heat escape and retention.
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I was simply saying a tall narrow pot vs a short fat one. There are many things that affect the boil off rate between the two beyond surface area.
 
Homercidal said:
Well technically isn't it the precursors to DMS that we are boiling off? DMS doesn't actually occur until later I think.
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The way I understand it is as follows: SMM is present in grain. When exposed to heat, SMM converts to DMS so this conversion occurs during the mash and boil. So, with that said, I think its a combination of both (i.e. you are boiling off both DMS and SMM which is the precursor I think you're referring to).

Someone please correct me if I am mistaken.
 
Bopper said:
The way I understand it is as follows: SMM is present in grain. When exposed to heat, SMM converts to DMS so this conversion occurs during the mash and boil. So, with that said, I think its a combination of both (i.e. you are boiling off both DMS and SMM which is the precursor I think you're referring to).

Someone please correct me if I am mistaken.
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There is an EXCELLENT Brewstrong podcast called DMS that very clearly covers this. Unfortunately, I can't help you with any real facts.
 
passedpawn said:
There is an EXCELLENT Brewstrong podcast called DMS that very clearly covers this. Unfortunately, I can't help you with any real facts.
Click to expand...

Cool, thanks. I'll check it out.

I found it in itunes. The brewcast is called DMS and was from 03/03/09. I'll report back after I have a chance to listen to it.
 
Ok, so I ran the experiment. I took an identical skillet and small saucepan from the same set of pots and filled them each with 1/2 cup of tap water. I marked a pencil dot on the inside of each to mark the fill line, then brought them to a boil. After verifying that they were both at 225 degrees, I then re-filled each with boiling water from the microwave up to the pencil dot so that they were both now at the same temp and equal amounts of water.

I let them both boil for 5 minutes and then dumped the contents of each into pyrex measuring cups. The skillet definitely lost more water than the small saucepan.

The setup:
boil1.jpg


Results from skillet:
boil2.jpg


Results from saucepan:
boil3.jpg


Of course, this is all shade tree science so who knows.
 
Bopper said:
EDIT - Just a point of clarification since this is in the beginners forum: DMS is only an issue with all-grain brewing. However, when brewing extract, I would still leave the pot uncovered in order to keep boil-overs at bay.

EDIT #2 - It's OK to leave the lid on while you get up to a boil in order to save some time. Once you start your timer for the boil, then you should take the lid off.
Click to expand...

I am brewing my first partial (http://www.austinhomebrew.com/product_info.php?products_id=12372) tomorrow and am having major concerns about my boil.

I have run several experiments i can get a good boil going but have to keep a lid on it.

I am wondering if DMS is a concern when brewing a partial or if it is only a concern for all grain.

The reason i ask for verification is because i cannot reach 212 degrees with a lid off - even after nearly 2 hours. it stays just shy (2 degrees - not a calibration issue).

im thinking about splitting the boils but i rather not if possible. so lid or no lid for my recipe?

im apologize for the dumb question but i have done a ton of preparation and dont want to mess up something simple.

:mug:
 

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