Boiling Sap on your Propane Grill: Is it Worth it?

March 19, 2018

Boiling sap to make maple syrup is something of a rite of passage when your homestead is in Vermont.  You have try it at least once, and if you find a system that works you just might get hooked. Especially once you taste a spoonful of the golden elixir right after it is boiled down. 


When we bought our homestead, we longingly eyed the almost half acre of sugar maples that we share with our neighbor.  The old sugar shack now serves as our shed, but the remnants of the boiling that they used to do on this farm lingered - an old tub that used to hold sap, plastic barrier now covering steam vents in the roof.  We just knew we’d be tempted.


We have plans in the works to partner with a local sugar maker to tap most of our trees and sell him the sap for his operation, but in the meantime we’re playing around with old-school tapping and backyard boiling methods. 


In a good year, about 40 gallons of sap make about 1 gallon of syrup. Boiling sap in your kitchen is not a great option. Imagine how much steam is generated from 39 gallons of water, onto all of the surfaces in your kitchen - a sticky mess!  Back yard alternatives are a must.



This year, we tapped 10 of the trees closest to our house and we experimented with two improvised back yard methods - the propane grill and a fire pit boiler. This article focuses on the propane grill; our next article will share results with the fire pit.  In both cases, we boiled using a continuous flow pan called “The Seedling Urban Evaporator” loaned to us by the Vermont Evaporator Company.


A NOTE ABOUT OUR PAN: One of our goals in experimenting with this method was to find a more efficient way to do it, hence the use of the Seedling Continuous Flow Pan.  This pan is actually sized to fit a typical backyard grill, because the McCabe Family at the Vermont Evaporator Company were also looking for simple backyard sugaring solutions. They knew that this grill top method was popular and could be improved.  The pan measures 17x23 inches, and is divided into four sections that allow the sap to move from one side of the pan to the other as it thickens (see photo below).  Then, where the thickest sap gathers, there is a spout to release the nearly-finished syrup.  New sap is poured into the left side each time the total volume in the evaporator reduces by half, which allows you to keep adding all sap day while the sap on the right side of the pan thickens up.  This pan retails for $295.




Using your grill to boil sap basically entails setting a large pan on top of the grill and letting it simmer and evaporate for many hours.  You’ll hear stories where people have used up to $40 in propane to make a quart of syrup which took two days to reduce down, usually because they are using a large pot with not much surface area.  While this method is fine for a one-time gig, I doubt too many people will choose to repeat this highly inefficient process. 


The Seedling pan increases the efficiency of this method, but you could also try a large hotel pan like this one – it will not fill the whole surface of your grill and lacks the continuous flow feature, but it does offer a larger surface area for steam to escape.  You would just keep adding sap as it reduced through the day.


Our Results:


The key to measuring the efficiency of any boiling method is the number of gallons of sap you can boil down in an hour.  In our experiment, we used a 30,000 BTU grill (on the low side when it comes to heat production – about 75 BTU’s per square inch) and boiled about 1-1.5 gallons per hour. After 14 hours of boiling, we reduced 16 gallons sap down to 3 quarts which we then brought inside and finished on the stovetop (to reach the boiling point of sap) and ended up with about 1.5 quarts of syrup.


NOTE: Back yard boiling methods do not always get the syrup up to the temperature necessary to finish it off.  Syrup boils at 7 degrees higher than water, which means that if water boils at 212 degrees you would have syrup when the sap that you have reduced down starts to boil and has reached 219 degrees (you may actually want to boil water at your house and take the temperature since the actual boiling point can vary based on elevation and pressure changes caused by weather systems).  In our experiments we found that it was best to boil as much sap as we wanted (or had time to do), reduce it down, and get it up to about 200 degrees throughout the different sections of the evaoporator.  We then brought the final batch into the kitchen and reduced it and brought it up to 219 degrees in a roasting pan on our stove. This process in the kitchen took about 15-20 minutes.



Another key measure is cost of materials – we filled one propane tank for about $15 and did not end up using the whole thing, which means we used less than $15 of propane to get 1.5 quarts of syrup.  Given the current cost of syrup is about $50/gallon this is a pretty reasonable exchange.  It does not take into account the cost of the pan – you would need to consider how many times you were going to boil to factor this in.


Based on our conversations with the Vermont Evaporator Company and our research on propane grills, we believe our results were on the slow side.  A higher BTU propane grill (many burn around 80-100 BTU’s per square inch) would speed up the process; the company’s original tester was able to boil 2 gallons per hour, which was much faster than any other basic pan he had used.  At that rate, we would have finished our sap in closer to 8 hours.  This would have been a more desirable solution, as boiling into the wee hours of the night makes the activity a little less fun! (Although it did remind us of the days to come this summer when we would be preserving our summer's bounty in the canner!).


Is it Worth It?


If you have a higher BTU grill and either the Seedling Evaporator Pan or a large hotel pan, this method might be a good choice, especially if you don’t want to invest too much time in a more permanent boiling solution.  If, for example, you want to tap 5 trees in your backyard and boil 2 or 3 times, you could probably rely on this method for a fun family activity, even if its not the best return on investment.  It’s also much easier than dealing with a fire pit.  You can literally set your timer to check the sap every 20-30 minutes and not have to do much to keep the process going.  This makes it a beginner-friendly option.


And really, any method that results in being able to taste your own freshly boiled maple syrup is worth it at least once a year!




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