Boiling is where sap becomes syrup, and it's the longest part of the process. You're boiling away almost all of the water: about 39 of every 40 gallons. It takes time, but a good setup and a few habits make it easy and a lot of fun. This guide covers the main boil. When your syrup gets close to done, move on to our finishing guide.
How much sap makes how much syrup
The rule of thumb is Jones' Rule of 86: divide 86 by your sap's sugar percentage to get the gallons of sap needed for one gallon of syrup.
| Sap sugar | Gallons of sap per gallon of syrup |
|---|---|
| 1.5% | about 57 |
| 2% | about 43 |
| 2.5% | about 34 |
| 3% | about 29 |
Use our Sap to Syrup calculator with your own numbers.
Boil outdoors
Boiling 40 gallons of sap puts about 39 gallons of water into the air as steam. Indoors, that much steam can peel wallpaper, soak drywall, and cause moisture damage. Do the main boil outside. Many backyard sugarmakers bring the nearly finished syrup inside to finish on the stove, where it's easier to watch the temperature (see the finishing guide).
Choose your setup
Propane burner and pan
A turkey-fryer style burner with a stainless pan is the easiest way to start. It's quick to set up, easy to control, and good for a handful of taps.
Block arch and pan
A simple firebox of concrete blocks with a pan on top, fueled by wood. It's cheap to build, holds a bigger pan, and has that classic sugaring feel. It takes more tending and more firewood.
Hobby evaporator
A purpose-built firebox and pan for small producers. It boils much faster and more evenly. A good upgrade once you're hooked.
Pick the right pan
- Wide and shallow beats deep. More surface area means faster evaporation.
- Food-grade stainless steel is the best choice.
- Avoid galvanized metal, lead solder, and old pans of unknown origin. They can put metals into your syrup.
How long will it take?
It depends on your pan, your heat, and the weather. A small home setup often boils off roughly 1 to 3 gallons of water an hour, so 40 gallons of sap can take most of a day. To find your own rate, mark the sap level, boil for an hour without adding sap, and measure how much went down. Then plug it into our Boil-Off Time calculator.
Keep the boil going
- Start with 1 to 2 inches of sap in the pan and bring it to a rolling boil.
- Add sap gradually as the level drops, keeping at least an inch or two in the pan. Adding a little at a time keeps the boil from stalling. Preheating sap in a pot on the side helps even more.
- Never let the pan run low. Thickening sap can scorch, and a dry pan can warp or burn through in minutes.
- Skim the foam and scum that rises to the top with a slotted spoon or skimmer.
Tip: If foam starts climbing toward the rim, a tiny dab of butter or a drop of food-grade defoamer knocks it down fast. Keep a spoon of butter nearby.
When to move to finishing
As you get near the end, the liquid turns golden, the bubbles get smaller and thicker, and the temperature starts climbing above the boiling point of water. When it's a few degrees below your finishing point, stop adding sap and move the batch to a smaller pot where you can control it closely. Our finishing guide takes it from there.
Why syrup turns out dark
- Sap that sat warm before boiling
- Very long boiling times, or boiling a small amount of sap for hours
- Light scorching on the pan bottom
- Late-season sap, which naturally makes darker syrup
Darker syrup isn't bad. It has a stronger maple flavor that many people prefer. But for lighter syrup, keep sap cold and boil it promptly.
Safety first
- Never run propane or wood fires indoors or in a garage. Carbon monoxide is deadly.
- Set up on a stable, level surface away from buildings, dry grass, and overhangs.
- Never leave a boil unattended, and keep kids and pets back from the fire and hot pan.
- Steam and boiling syrup cause serious burns. Wear gloves and use long-handled tools.
- Keep a fire extinguisher or water nearby.
Ready for the next step? Read How to Finish Maple Syrup, or go back to collecting and storing sap.