Question about boil off

[CUBrewing]

I use a 16 gallon pot as my boil kettle. It has a larger diameter than most other boil pots I have seen and I seem to boil off like 3 gallons or more on a 60 min boil for a five gallon batch. I was wondering if the increased surface area could cause this or could I be boiling to vigorously?

 

[jCOSbrew]

I get about 1 gal/hour boil off in a 10 gallon pot on a bayou classic burner.

I would turn down the heat and save some propane. The wort is the same temp whether it is a slow boil or a vigorous boil.

 

[CUBrewing]

I get about 1 gal/hour boil off in a 10 gallon pot on a bayou classic burner.

I would turn down the heat and save some propane. The wort is the same temp whether it is a slow boil or a vigorous boil.

I have seen where some people say that it is important to have a full rolling boil though

 

[duckredbeard]

Absolutely the large surface area is contributing to your evap rate. I use a converted keg and try to keep about 1/3 of the surface covered with boil foam. It isn't science.

I just know that typically works for me. Preboil is 7.5 gal, 90 min boil gets me to 5.25 gal. By the time I ferment and rack a few times, I have 5 gal.

 

[duboman]

I use a 16 gallon pot as my boil kettle. It has a larger diameter than most other boil pots I have seen and I seem to boil off like 3 gallons or more on a 60 min boil for a five gallon batch. I was wondering if the increased surface area could cause this or could I be boiling to vigorously?

The increased surface area is the culprit but also 3 gallons is a lot! While you do want a vigorous boil to drive off DMS it sounds like you can drop your heat a bit to reduce the rate of evaporation.

There are also environmental issue to contend with like wind, temperature, humidity, etc as these conditions will also increase or decrease the rate of evaporation as well.

I have found that when I brew in the winter with the cold dry air I will lose about 1.25 gallons, on a normal spring/summer day about a gallon and if it's really hot and humid about .75 gallons.

 

[matt2778]

Pot diameter is by far the biggest factor in boil off. I have a 15 gallon aluminum (18" diameter) and I typically boil off 2 gallons an hour. When I was using my smaller 8 gallon pot (14"dia) I was only boiling off just over gallon. As long as your hitting your post boil volumes I wouldn't sweat it to much.

 

[passedpawn]

I disagree with most here. It's the larger base that is giving you much greater boil-off, not the opening at the top. This might seem like semantics, but it's not.

First, evaporation and vaporization are two different things. Evaporation does occur, and the opening size does affect it, but the majority of the boil-off is caused by vaporization at the bottom of your pot. That's where the heat is being applied. When the base gets bigger, the flame can more efficiently heat the pot and you get more vaporization.

The water is vaporized at the bottom of the pot, not at the surface. Watch a boil. The reason the water is churning is because of these vapors racing up from the bottom. The surface area is not important to vaporization.

 

[logdrum]

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[logdrum]

I disagree with most here. It's the larger base that is giving you much greater boil-off, not the opening at the top. This might seem like semantics, but it's not.

First, evaporation and vaporization are two different things. Evaporation does occur, and the opening size does affect it, but the majority of the boil-off is caused by vaporization at the bottom of your pot. That's where the heat is being applied. When the base gets bigger, the flame can more efficiently heat the pot and you get more vaporization.

The water is vaporized at the bottom of the pot, not at the surface. Watch a boil. The reason the water is churning is because of these vapors racing up from the bottom. The surface area is not important to vaporization.

Thank you Dr Science!

 

[duboman]

While it is true that vaporizing and evaporating are two different actions they are both related to each other. You are correct in that the wider base increases the rate of vaporizing the same holds true for the greater surface area in its relationship to the rate of evaporation.

If you were to use two vessels of the same base diameter and the same volume delivering the same heating rate the vaporization would be equal but if one vessel had a smaller diameter surface area exposed to less air and environmental conditions the rate at which evaporation occurs would be less. You would wind up with less final volume in the wider opening vessel.

For example, when I used to make starters I used to use a sauce pot to boil before transferring to a mason jar. I now use an Erlenmeyer flask. The bases of the two vessels are the same diameter as well as the same stove and heat supply but the flask is much narrower in the opening. I boil the same amount of time with the same starter volume. With using the flask I now get a larger final volume of starter wort after a 15 minute boil than I did with the sauce pot.

I know this is not an exact science comparison but it does illustrate my point. In truth I believe we are all correct to some degree

 

[StMarcos]

This is more or less correct. Evaporation is inconsequential when you're boiling wort. Power in (above the power needed to keep at boil temp (loss through sides)) = vape rate.

I disagree with most here. It's the larger base that is giving you much greater boil-off, not the opening at the top. This might seem like semantics, but it's not.

First, evaporation and vaporization are two different things. Evaporation does occur, and the opening size does affect it, but the majority of the boil-off is caused by vaporization at the bottom of your pot. That's where the heat is being applied. When the base gets bigger, the flame can more efficiently heat the pot and you get more vaporization.

The water is vaporized at the bottom of the pot, not at the surface. Watch a boil. The reason the water is churning is because of these vapors racing up from the bottom. The surface area is not important to vaporization.

 

[smoothbean]

I disagree with most here. It's the larger base that is giving you much greater boil-off, not the opening at the top. This might seem like semantics, but it's not.

First, evaporation and vaporization are two different things. Evaporation does occur, and the opening size does affect it, but the majority of the boil-off is caused by vaporization at the bottom of your pot. That's where the heat is being applied. When the base gets bigger, the flame can more efficiently heat the pot and you get more vaporization.

The water is vaporized at the bottom of the pot, not at the surface. Watch a boil. The reason the water is churning is because of these vapors racing up from the bottom. The surface area is not important to vaporization.

pots are the same size top and bottom? I don't under...never mind