Evaporation rates

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chardo

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How do I estimate my boil off rate? More heat more surface area = more gph This is realy a question about making Maple syrup. I asked in general chit chat but haven't had a good answer. Any help would be great.

Thanks
Chardo
 
I don't know how to calculate it. The easiest way is probably to put a set amount of liquid in your kettle, boil for 60 or 90 minutes, cool it, and re-measure the volume.

Boil-off will depend on how big of a flame you are applying and the geometry of your kettle (the amount of surface area exposed for evaporation) , plus it can vary depending on your ambient temperature, humidity, etc.
 
10 Gallons of sap on a turkey fryer in 40 degree weather takes all day, a couple of propane tanks, a ton of homebrew and a lot of patience to get down to 1 quart. And you want it to be 40 to 1.
 
I kept coming up short after my boil. So I spent a day boiling water. I wanted to end with 5 gal. so I started at 6, then 6 1/2, 7. Figured I boil off between 1 1/2 and 2 gal an hour of water. Took all day and a lot of gas, but seems to get me closer in the end. Only trouble is that was in January at 20-25 deg F. with dry winter air. I'm sure I'll be over when spring and summer gets here.

Anyway that is how I figured it out. May help someone.
 
10 Gallons of sap on a turkey fryer in 40 degree weather takes all day, a couple of propane tanks, a ton of homebrew and a lot of patience to get down to 1 quart. And you want it to be 40 to 1.

Wouldn't a quick trip to the grocery for a bottle be a LOT cheaper than two tanks of propane? </smart-ass response>

Sorry, I admire your fortitude though. Just seems like a lot of work for little return.
 
All true Vermonters must at least once boil sap for an entire morning and afternoon. If you're doing it with your kids as a project, they will lose interest about 10 minutes into it. If you're having your buddies over for brews, they will be kicked out by wife somewhere around mid afternoon.
 
I was thinking about doing this as well at one point. I was planning on getting one of the 6" deep strap pans we used to use in a commercial kitchen (Probably 2'x3'x6") and build a pit out of bricks, then fire it with wood. I get wood for free so then I wouldn't be paying for all the propane, and it would need to boil for a long time, but the pan would give me more surface area. I'd just keep pouring in more sap as it boiled down.

Unfortunately I only have 1 maple tree and though I could get enough sap out of it over the whole season, sap does not store well, so I couldn't save it all up and do it in one day easily.
 
Just sneak out at night and pop the neighbor's trees. Tell them that there is a really large woodpecker in the area to explain the hole.... If they catch you with the bucket, you are on your own....
 
I was thinking about doing this as well at one point. I was planning on getting one of the 6" deep strap pans we used to use in a commercial kitchen (Probably 2'x3'x6") and build a pit out of bricks, then fire it with wood. I get wood for free so then I wouldn't be paying for all the propane, and it would need to boil for a long time, but the pan would give me more surface area. I'd just keep pouring in more sap as it boiled down.

Unfortunately I only have 1 maple tree and though I could get enough sap out of it over the whole season, sap does not store well, so I couldn't save it all up and do it in one day easily.

if you get a good season you can get 10 gallons in two weeks from a tree. 5 gallons would be enough for a pint. lot of work for that much. store it in a rubber trash can with lid outside for that time. as long as it doesn't turn milky you can boil it.
 
So how do I figure an evaporation rate? I need to size the equioment I'm building and how many taps to set.

Chardo
 
All true Vermonters must at least once boil sap for an entire morning and afternoon. If you're doing it with your kids as a project, they will lose interest about 10 minutes into it. If you're having your buddies over for brews, they will be kicked out by wife somewhere around mid afternoon.

I can totally understand this mentality. I would do it at least once. I am in the process of building a cold smoker so that I can start smoking my own salmon. It will take like 3 days to completion for the brining and smoking. I'll end up with five pounds that costs me . . . nevermind. Bad example. I'll get like $100 worth of primo salmon from an investment of about $30 in ingredients.

Is there sugar conversion going on with maple syrup. Or is it strictly concentrating the sugars. I am wondering if the cook can be seen in the finished product. That is the type of specialty products I like to make.

Coffee is another example. I have a steady 30-40 customers who insist that I roast the best coffee they have ever had. They have done the search for it too so I feel partucularly flattered but not too surprised because I felt that way before I ever even had customers.
 
yes but the heat of the evaporation does have an effect on the final color of the syrup. the same malliard reactions that darken your wort on a long boil also darken the maple sap.
 
So how do I figure an evaporation rate? I need to size the equioment I'm building and how many taps to set.

Chardo

This has been a stumbling block for me. In my software (Beersmith) they want an evaporation rate, instead of volume boiled off. I used 15 to start with just to see how it went and I think that is just about right. However, you have to make sure you maintain the same flame intensity every time or the evap. rate will change.

It's really a matter of trial and error IME unfortunately; 15% is a good starting point IMO. About 1 - 1.5 gallons
 
I ran a test with my new gear yesterday, using a stovetop plus a 950W heatstick. The evaporation rate for me with plain tap water came in around 17% (about 2 gallons over a 90 minute boil, with the starting volume at 170 degrees). I tried to make the conditions as close as I could to actual brewing conditions so that my estimate would be close to what I'd really end up getting.
 
Trial and error, keep good notes. Then you figure out how much you need to start with to finish with a certain volume. Of course evaporation will likely be a little different each time depending on how rapid the boil is.
 
By the way, why do we measure evaporation rates in percent? This would imply that less and less water boils off over time. For example, let's start with 10 gallons and evaporation rate of 10% per hour.

10.0 gal @ 0 hrs.
9.00 gal @ 1 hrs.
8.10 gal @ 3 hrs.
7.29 gal @ 4 hrs.

If you keep doing the numbers, you will NEVER hit zero gallons, so clearly the percent model is wrong. If anything, evaporation should occur faster with less volume as time goes along, but I think a constant rate of x gal/hr. is a better model.
 
Maybe the percent number just means the percentage of the original volume that boils off per hour, so it is constant.
 
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