Any negative effects using a smaller boil keggle top openings?

After reading another thread posted about a boil pot with a 18" diameter asking if that would increase more boil off volume that made me think and ask a few questions almost on the same topic.
First off that 18" diameter boil pot would result in 254 sq/in surface area, a 12" cut keggle 113 sq/in surface area, going down to 10" cut keggle to 78.54 sq/in surface area.
Going from diameter 18" down to 12" reduces this surface area to .444 of 18", 18" to 10" reduces this surface area to .308 and 12" to 10" to .694 of a 12" opening.
Questions; would there be any ill effects with having a boil keggle with 10" vs a 12" opening on the keggle? Any nasty by products that need to be boiled out that a smaller opening might hinder their excape using 10" vs a 12" opening? I know the boil off times to reduce the volume would take longer with a smaller opening, any other reason why this would not work?

Which really has an effect on the boil off... the actual surface area of the wort or the opening through which the steam escapes? If you're using a keg as a keggle and just throttling down your opening I'd wonder if it'll make that much difference in boil off rate. (But I'm FAR from an engineer, and especially a thermal one!)

Just from personal experience and readings/podcast listenings, I would think the difference would be unnoticeable.

However, I have this nagging thought in my head that I heard/read somewhere that if the baddies that boil off get caught on the rim and drip back into the keggle late in the boil, then it could hurt ya...I don't know if that's true or not though.

I am really new to this, so does this mean that with the kettles with larger openings will reduce boil off time? im thinking that would be a good thing?? I am the guy with the 18 inch pot, but like i said i am new to this.skip...

woog11 said:

I am really new to this, so does this mean that with the kettles with larger openings will reduce boil off time? im thinking that would be a good thing?? I am the guy with the 18 inch pot, but like i said i am new to this.skip...

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A larger diameter kettle (more surface area) will boil off more liquid in the same amount of time. You just need to start with the right amount of wort in the kettle to hit the desired volume at the end of the boil. Varies for every brewers' method and system - takes a few batches to dial it in.

The narrower opening will also increase the likelihood of more boil overs as it is like putting a lid on the pot.

Linc

Major breweries have covered boil kettles. There's an awful lot of drip-down. They vent the steam through chimneys to the exterior of the building....some actually use the steam to heat the building. I know New Belgium has gotten several "eco-awards" for doing this very thing.....

missing link said:

The narrower opening will also increase the likelihood of more boil overs as it is like putting a lid on the pot.

Linc

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This I must disagree on as a pot on the stove with any liquid near a boil will not boil over even with a lid added covering almost 3/4 of the pots surface area. Placing the lid fully on yes your headed for a boil over rather quickly even with the heat reduced by app 40% of the heat applied before without any lid. As an example the keg ID is 15.6" diameter this is 191 sq/in in area, a 10" opening is 78.54 sq/in in area. 191/78.54 = 41% of total keg surface area.
I find this hard to believe this reduction amount would cause boil over problems that a little heating control readjustment or lowering can not handle.

I was more concerned about any nasties that must be boiled out if there are any unless i'm reading or adding more than what is required in brewing.

ScubaSteve said:

Major breweries have covered boil kettles. There's an awful lot of drip-down. They vent the steam through chimneys to the exterior of the building....some actually use the steam to heat the building. I know New Belgium has gotten several "eco-awards" for doing this very thing.....

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In that case with what you posted about "Major breweies have covered boil kettles. There's an awful lot of drip-down".

This tells me that there must be no worries about nasties getting trapped and not boiled out.
Boiling too long also reduces the hops oils and flavors hence adding more later towards the end of the boil time again.

With less water boiled down per given amount of time be it a 60 or 90 minute boil time this will allow for more net product at the end for the frementer.
With a large grain bill like a big Stout requiring 48.5 pounds of grain (off memory here would require 19.04 gallons of MLT volume).
After two or three trub and yeast dumps there still will be over 15 plus gallons in the fermenter to fill three 5 gallon corny kegs full.
I'm talking a MLT and boil keggle capable of holding 22 gallons of liquid.

The extra material on the keggle top from a cut 10" hole to the side of the keggle would allow more material to add vertical fittings plus a stainless sleeve for adjustment of the sparge ring heigth above the different mash levels.

I have a 12" hole in the top of my keggle. It fits a convenient pot lid I have. The disadvantage I'd give on having a smaller opening, is that it's harder to see what's going on in there, because a lot more steam is held in place. If I did not use the keggle for other purposes, I'd cut a larger opening. I think my next keggle for a 3 tier setup will have a larger opening and this one will be a HLT.