Boil-Down
Maple sap is boiled to remove water and concentrate the sap to syrup. A lot of moisture is created in the boil-down process. Therefore it is important to choose a well ventilated location, preferably outside. I recommend using an open fire pit as a heat source. However a similar procedure may be used for any other heat source. Other popular sources of heat include gas barbeques and woodstoves. It is important to bring the sap to a fast rolling boil as this will drastically decrease the time required to boil of the excess water.
When boiling maple sap you can use this simple formula to roughly estimate how much water must be boiled off:
40 Littre of sap = 1 Littre of Syrup
*Note – The ratio varies depending on the sugar content of the sap, ratios from 30:1 to 40:1 are possible
If you have 20 liters of sap you need to boil it down to approximately ½ liter. I recommend that you remove the sap when it approaches the 40:1 ratio and do the final boil-down in a smaller pot on a stove or gas barbecue. Great care must be taken as it is extremely easy to burn the sap when it gets close to the 40:1 ratio.
When the syrup is done you should filter it to remove any ash or other contaminants. A clean cheese cloth works well, and should be used while the syrup is still hot.