36 X 36 Flat pan

[Trapper2]

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I do all my cooking on a flat pan, once its going in 15 minutes or so I keep it at a rolling boil feeding it with a trickle from my preheat tank. My pan has 6 inch sides on it and I usually keep 4" of sap in the pan. Would I evaporate more GPH if I only kept 2" of sap in it or doesn't it really matter as long as you maintain the boil?

Thanks, Trapper

[tcross]

you'd be better off keeping the level at 2", or more like 1" or 1 1/4". less liquid in there pan equals faster evaporating.

[wmick]

Can anyone explain the thermodynamics or physics to explain why shallower sap evaporates faster? I don't doubt it, because I've heard it too many times for it not to be true.... but with the exception of longer start up time (getting the extra volume to boiling point), I have a hard time understanding why throughput will be faster. I would love to understand if anyone cares to explain it..
Thanks

[SPILEDRIVER]

its a matter of the energy needed to heat the sap...takes a lot less energy(btu's) to keep 5gallons of sap boiling at 1 inch depth than 15 gallons boiling at 3 inch depth...

[pyro]

Increased depth creates more exposed surface area on the side of the pans and will lose heat to the ambient cold air. That said, I don't see any noticeable effects of boiling deep. The backside of my pan gets heat leaking through going to the flue so it actually helps me on that side.

I will also mention I'm on thick pans which are slower to respond and retain heat longer (although are less efficient). I don't see why that would change anything with sap depth, but just stating it since many others seem to say they see a difference in depth. I think they're just impatient :)

[mellondome]

Increased depth also increases the distance the bubble has before breaking the surface. Which increases the likely hood that it wont break the surface, but condense back to water in the pan.

[CharlieVT]

Can anyone explain the thermodynamics or physics to explain why shallower sap evaporates faster? I don't doubt it, because I've heard it too many times for it not to be true.... but with the exception of longer start up time (getting the extra volume to boiling point), I have a hard time understanding why throughput will be faster. I would love to understand if anyone cares to explain it..
Thanks

Interesting question, I'm trying to get my head around this question:
Dusting off the memory banks of some physical chemistry I once knew and a quick "google" on the subject,

Primary factors affecting rate of evaporation:
The big factors: surface area exposed to the atmosphere (bigger pan boils faster), temperature (hotter fire boils faster), atmospheric pressure and relative humidity (higher pressure and relative humidty will reduce rate of evaporation).

Depth of the liquid is less significant. It will take longer to come to temperature at start up since more liquid must be heating to boiling point, but once the temperature of evaporation is reached, the same amount of heat energy will result in an equal rate of evaporation regardless of depth with the following exceptions: Increased surface of the sides of the container (pan) will result in some increased cooling of the sap, but probably not all that significant unless you are boiling outside and the wind is blowing (under these circumstances your pan becomes a heat radiator). A little wind can actually increase the rate of evaporation: a gentle breeze over the pan will increase boiling but blowing away water molecules just evaporated from the surface thus decreasing humidity at the surface.

How I think this applies to sugarmaking:
My understanding of the reason sugarmakers seek a shallow depth of sap in the pan is to get lighter syrup. A deep pan results in sap being boiled longer, resulting in increased caramelization of the sugars hence darker syrup. This is not because the rate of evaporation is being significantly reduced, but rather due to more sugar molecules staying the the pan and being "cooked" longer before being drawn off. By running pan shallow, you are able to draw off a smaller amount of syrup sooner, by running deep you boil longer to evaporate a larger quantity of water and ulimately will draw off a larger, but darker batch of syrup.

So the reason to run sallow is to get lighter syrup, but it doesn't significantly change the rate of evaporation. Running shallow will increase the frequency of draw off which may give the impression of faster evaporation.

Does this make sense?

[Quebecguy]

Does this make sense?

Yes, CharlieVT, I think that makes perfect sense. To maximise the syrup quality, minimize the depth of sap in one's pans. Within reason of course. I keep enough depth in the front pan to insure the solder doesn't melt and this depth increases in direct proportion to the number of visitors in the sugarhouse! Boiling by myself I keep an inch of sap or less in the front pan but with the distraction of visitors I might go up to an inch and a half or even two inches.

[Super Sapper]

For whatever technical reason depth does play a significant part in evaporation rate. Depending on size of evaporator the difference from 1 inch to 2 inches can be several gallons per hour. It may be that as you can not get the liquid any higher than its point of evaporation (which occurs where the pan meets the heat) it cools just slightly as the vapor is trying to escape and some condenses. The longer the bubble has to travel through the liquid the more chance some will condense.