Boil off Rate: 10gal vs. 20gal kettle

[DVCNick]

So I've Googled around and opinions seem quite varied (?), so I'm looking for anecdotal experience:

I'm planning my first 10 gallon batch hopefully this weekend, and I've got a new 20 gallon kettle to use for it.

Is my boil off rate likely to change?
Average of my last ten 5 gallon batches in the 10 gallon kettle: 4.1qt/hr boil off. Exposed surface area of the liquid is 1017 square cm.

Surface area in the new kettle is going to be about 1590 square cm, almost 60% increase from the old kettle. I'm sure there is real science on whether this matters at all, but what have you actually observed in this situation? Should I assume a proportionally increased boil off rate, no change, something else? Thanks.

 

[Dgallo]

So I've Googled around and opinions seem quite varied (?), so I'm looking for anecdotal experience:

I'm planning my first 10 gallon batch hopefully this weekend, and I've got a new 20 gallon kettle to use for it.

Is my boil off rate likely to change?
Average of my last ten 5 gallon batches in the 10 gallon kettle: 4.1qt/hr boil off. Exposed surface area of the liquid is 1017 square cm.

Surface area in the new kettle is going to be about 1590 square cm, almost 60% increase from the old kettle. I'm sure there is real science on whether this matters at all, but what have you actually observed in this situation? Should I assume a proportionally increased boil off rate, no change, something else? Thanks.

Did your kettle company give you the specific ratio the kettle is made to be? Most companies will follow a specific one for boil off rate

 

[DVCNick]

Both are Megapots. This is the 20gal one: https://www.northernbrewer.com/products/20-gal-megapot-1-2

I'm just using the listed internal diameter to calculate the surface area... is that the ratio you are talking about?

 

[Dgallo]

Both are Megapots. This is the 20gal one: https://www.northernbrewer.com/products/20-gal-megapot-1-2

I'm just using the listed internal diameter to calculate the surface area... is that the ratio you are talking about?

Yeah I was looking to see if your pot was 1.2:1 which is stadard. I have a 20 gallon pot with the same ration and I have a boil off about rate of about 12.5% with 6.75-7galof wort going into the kettle preboil and finish with just about 5.75-6galon. If never done a 10 gal batch but it’s understanding my understanding is that as you increase the batch volume in the same pot, the volume boiled off remain very similar to a smaller batch but your boil off percent will fall

 

[RPh_Guy]

With larger batch and larger kettle and all other factors equal:
Boil off rate should go down a little, mainly due to increased heat loss from larger surface area.

The amount of heat applied to the wort is the main factor determining your boil off rate, not the kettle dimensions (although that does have an effect). If you care about thermal damage to your wort, you'll want to target about 4-10% boil off per hour.

The heating and cooling times will double, approximately.

 

[DVCNick]

Yeah I was looking to see if your pot was 1.2:1 which is stadard. I have a 20 gallon pot with the same ration and I have a boil off about rate of about 12.5% with 6.75-7galof wort going into the kettle preboil and finish with just about 5.75-6galon. If never done a 10 gal batch but it’s understanding my understanding is that as you increase the batch volume in the same pot, the volume boiled of remain very similar to a smaller batch but your boil off percent will fall

Ah gotcha. Yeah looks like it is right near 1.2/1 height/diameter.

To me it makes sense that the exposed surface area of the liquid would play a significant role in the boil off rate, and all else equal, it would scale linearly with said available surface area... but, that is just my WAG.

Sounds like you're losing about the same amount in your 20gal pot as I am in my ten gallon pot though, which would not support my theory.

 

[DVCNick]

With larger batch and larger kettle and all other factors equal:
Boil off rate should go down a little, mainly due to increased heat loss from larger surface area.

The amount of heat applied to the wort is the main factor determining your boil off rate, not the kettle dimensions (although that does have an effect). If you care about thermal damage to your wort, you'll want to target about 4-10% boil off per hour.

The heating and cooling times will double, approximately.

I try to keep the boil pretty low. Definitely not a raging boil. Just enough to see it churning.

I cited my average at just a hair over 1gal/hr, but, my measurements aren't exact (I'm just eyeballing based on the gallon mark graduations in the kettle... kind of wish it had quart graduations). Also, in that average I had numbers all the way from mid 3's to mid 4's quart loss, and that spans seasons also... so if summer vs. winter is a major factory, it could be at play as well.

I guess I'll just assume one gallon and see how it turns out... if it's more I'll just have a tad more punch in my ale.

 

[RPh_Guy]

kind of wish it had quart graduations

Get a yardstick to use as a dipstick and calibrate your own markings.

 

[jrgtr42]

With a new kettle, I'd recommend doing a test boil - maybe not full volume, but half? Get an idea of how long to boil (yeah, it's not exact scale, but you'll be rough) and boil off of a given time.

 

[DVCNick]

Did the first 10gal batch today. Just decided to wing it.
My observed boil off rate was very near the absolute number I see for 5gal batches: +/- one gallon per hour. 4.1qt in this case is my best guess. Everything except kettle size was the same as always.

Definitely have to work a little harder and longer for the 10gal batch, but my first impression is that you have, on the whole, about a 20% greater time commitment for a 100% greater amount of beer, so... I like it.

I had 7.7 gallons of strike water and 22.5lb of grain, and my 10gallon mash tun was FULL. Required 3 sparge steps and got over 80% efficiency which is definitely high for me. I was expecting to take a slight hit in efficiency but it seems to be the opposite at least with this batch.