[gmac]

I've decided to build a bigger fermenter and I have a couple questions.  In particular, does the diameter of the vessel matter?  I know if it was a pot it would impact boil-off rates but in a closed fermenter, does it matter if the fermenter is tall and skinny or narrow and wide? 

I'm looking to build something of about 15 to 20 gal capacity and we've ordered a 4X8 sheet of stainless to get started.  But, the dimension is clearly one of the key points to consider before we start cutting anything. 
I'm lucky that I have a good friend who has a machine shop and is slow right now so we are going to have the steel rolled to dimension and then a seam welded. He has a very good TIG welder on staff so I'm not that concerned about the weld as it will be done well and ground.  We're also looking at having a cone rolled for the bottom and welded. 

The other consideration was, would it make any sense to have the entire fermenter made conical?  Instead of having straight sides attached to a cone, would it make sense to have it all as a cone and weld wedges on the exterior to bolt legs to.  The lid will likely be formed with an o-ring groove and clamps to hold it in place.  Any other thoughts?  I've looked at some on-line and I don't know if I like how the lid attaches on some of them.
Thanks for the advice.

[denny]

Fermenter geometry does have an affect on fermentation.  A tall narrow fermenter will exert more pressure on the yeast than a wider shallower one.  My understanding is that will place more stress on the yeast and produce different flavors.

[gmac]

I wonder what the commercial ones look like.  Anyone have a commercial fermenter that they can tell me the ratio of diameter to height?  Then, I could just scale down accordingly.

[tschmidlin]

It does have an effect, but it should be pretty small at the 10-20 gallon scale.  It's not like you're talking about making it 10 feet wide and 1 inch deep, or 1 foot wide and 7 feet deep.  Within the normal range for the volume and shape you're proposing, there won't be too much difference.

I wouldn't go all cone, I think that would make it too big at the top and a weird shape to be easy to handle.

[bluesman]

On a Brewstrong session, Jamil made note of the fact that fermenting 5 gal of beer in a 15 gal conical will tend to produce more esters than it would had you been fermenting 1o gallons of beer due to an increased amount of pressure on the yeast. Palmer agreed as well. Although, I'm uncertain as to how they confirmed this information.

I have a 14.5 gal conical fermenter that I've used to ferment 5 gal of beer and I have noticed and increase in esters from an aroma and flavor standpoint but this was based from batch to batch and not a side by side comparison. I really need to do duplicate back to back batches (5 and 10 gal) then do a blind tasting.

[richardt]

Check this out:  http://www.toledometalspinning.com/hopper/default.php

The cone should be 60 degrees (read that somewhere). 
It is steep enough to allow yeast and trub to slide and settle towards the apex of the cone (though you sometimes see pro-brewers whacking the larger cones with rubber mallets to try and get the yeast and trub to settle further down the cone).

Keep in mind that, given the same radius and height, the volume of a cylinder is 3 times that of a cone. 
You can ferment more beer in less space with a cylinder. 
This is an important consideration if you're using a keezer or refrigerator. 
To use a 27 gallon fermentor, you'd need 24 x 24 x 36 inches (minimum), preferably 26x26x38 inches or more.  See the Blichman website listed below (click on "data" tab).

If doing it from scratch, I'd basically copy the profile of a 20 gallon brew kettle and put a 60 degree cone on the base; basically giving yourself a 26.67 gallon fermentor (assuming you go with a flat lid). 
Consider using FermCap-S to limit the excessive krausen -- it'll help prevent blow-off problems.

Check out the 27 gallon fermentor Blichmann makes http://www.blichmannengineering.com/fermentor/fermentor.html

[tschmidlin]

On a Brewstrong session, Jamil made note of the fact that fermenting 5 gal of beer in a 15 gal conical will tend to produce more esters than it would had you been fermenting 1o gallons of beer due to an increased amount of pressure on the yeast. Palmer agreed as well. Although, I'm uncertain as to how they confirmed this information.

I have a 14.5 gal conical fermenter that I've used to ferment 5 gal of beer and I have noticed and increase in esters from an aroma and flavor standpoint but this was based from batch to batch and not a side by side comparison. I really need to do duplicate back to back batches (5 and 10 gal) then do a blind tasting.

How did they account for changes caused by the increased headspace?  There will be a lot more O2 left that can diffuse into the wort with the fermenter 1/3 full than when it is 2/3 full, especially if they are using straight O2.  It's just not as straightforward as doing two batches like that.

[bluesman]

On a Brewstrong session, Jamil made note of the fact that fermenting 5 gal of beer in a 15 gal conical will tend to produce more esters than it would had you been fermenting 1o gallons of beer due to an increased amount of pressure on the yeast. Palmer agreed as well. Although, I'm uncertain as to how they confirmed this information.

I have a 14.5 gal conical fermenter that I've used to ferment 5 gal of beer and I have noticed and increase in esters from an aroma and flavor standpoint but this was based from batch to batch and not a side by side comparison. I really need to do duplicate back to back batches (5 and 10 gal) then do a blind tasting.

How did they account for changes caused by the increased headspace?  There will be a lot more O2 left that can diffuse into the wort with the fermenter 1/3 full than when it is 2/3 full, especially if they are using straight O2.  It's just not as straightforward as doing two batches like that.

Tom...it's been a while since I've listened to that session and I'd have to go back through the sessions i order to accurately recap the info. but I believe it's the Brewstrong session "Fermenters" on 9/7/2009. They made mention of head space and O2 levels as well. It's a dynamic environment but fermenter geometry and size play important roles on ester production. Check it out if you can get a chance.

[tschmidlin]

Tom...it's been a while since I've listened to that session and I'd have to go back through the sessions i order to accurately recap the info. but I believe it's the Brewstrong session "Fermenters" on 9/7/2009. They made mention of head space and O2 levels as well. It's a dynamic environment but fermenter geometry and size play important roles on ester production. Check it out if you can get a chance.

I'll listen when I get a chance.  I have no doubt that it plays a role, but I am skeptical that there is much difference at homebrew volumes.

[gmac]

So if I do my math properly, a 1.2 foot by 3 foot cylinder would have a volume of approximately 23 US gallons.  The diameter of a circle with a circumference of 4 feet would be 1.2 feet.  That way we start with one cut across the sheet of steel.  The volume of a cone 1.2 X 1.5 feet would be about 4 US gallons so the total should be pretty close to 27 gallons.  This is likely taller than the Blichman models (I already checked them out on-line looking for dimensions).  This is a bit bigger than I was looking for but I could always cut the ht down a bit.  Volume of a cylinder 2.5 feet high is 21 gallons and the cone adds 4 for about 25 total.  Still more than I was originally intending but probably workable with upside volume.

Does this make sense?  That's about a 2:1 ratio of ht to width.  
I'll try to remember to take pictures.

Now, how to boil 30 gallons???  And does Coleman make a 45 gallon cooler???  Who's gonna drink all this beer???

[richardt]

How big is your fridge?  You're not going to be able to lift the thing when it is full.  Do you have some way of lifting or transferring it with pulleys/chains or overhead rack?

[denny]

How big is your fridge?  You're not going to be able to lift the thing when it is full.  Do you have some way of lifting or transferring it with pulleys/chains or overhead rack?

Yep.  It's one thing to have a big fermenter...it's entirely another to be able to control the temp in a fermenter that size.

[gmac]

My ratio of ales to lagers is about 10:1 so far.  It gets pretty cool here in the fall/winter/spring with ambient basement temps about 60 degrees.  I'm thinking that I would not be refrigerating this much.  If I wanted to do a lager, I'd be back to using buckets in the fridge but for ales, I'm thinking I would be good at least 9 months of the year.  Hopefully with bigger volume I will be able to get some volume ahead for the hot months (and with the airconditioner in the house running, the basement goes back into the 60's pretty fast).  I expect that this larger volume will produce more heat during fermentation than a smaller volume so I may be unpleasantly surprised though.
Is there a reason for refrigerating that I am missing?  I fully expect to have to rely on pumps to move wort/beer as I know this is far too heavy to lift.

[morticaixavier]

Now, how to boil 30 gallons???  And does Coleman make a 45 gallon cooler???  Who's gonna drink all this beer???

there is that post about an 880k btu burner! I would think that, except for high gravity brews the coleman 100qt would do the trick even at 15-20 gallons batches. could be wrong on that though.

[tom]

Tom...it's been a while since I've listened to that session and I'd have to go back through the sessions i order to accurately recap the info. but I believe it's the Brewstrong session "Fermenters" on 9/7/2009. They made mention of head space and O2 levels as well. It's a dynamic environment but fermenter geometry and size play important roles on ester production. Check it out if you can get a chance.

I'll listen when I get a chance.  I have no doubt that it plays a role, but I am skeptical that there is much difference at homebrew volumes.

+1
I think "they" now think that the effect is from hydrostatic pressure, thus the height of the fermenter, not the height:width ratio.