Why so much sap?
Sap is about 2% sugar and finished syrup is about 66–67.5% sugar, so roughly 40 litres of sap make 1 litre of syrup. Sweeter sap needs less; see the Rule of 86 in the deeper science.
Safety basics from UMaine Extension:
- Boil outdoors (an outdoor burner, hobby evaporator or fireplace), not on an indoor stove without strong ventilation: boiling sap releases a lot of steam.
- Never leave boiling sap unattended, especially over a wood fire. If it boils dry it can scorch and ruin the pan.
- Keep at least about 4 cm (1½ in) of sap in the pan.
How do you know it’s done?
UMaine Extension says syrup is finished at about 4 °C (7.1 °F) above the boiling point of water where you are. That boiling point changes with elevation and weather, so check it on the day. A syrup hydrometer is the most accurate check.
Why does the sugar level matter so much?
Below about 66% sugar, syrup can ferment or go mouldy. Much above about 69%, sugar crystals can form in storage. Finished syrup is filtered hot, and UMaine describes hot-packing it at about 82–88 °C (180–190 °F). Discard syrup that grows mould, and refrigerate opened containers.
Sources
- Ontario Maple Syrup Producers’ Association, Maple Products. ontariomaple.com
- University of Maine Cooperative Extension, Bulletin #7036, How to Tap Maple Trees and Make Maple Syrup (2025 update). extension.umaine.edu