The maple sap mystique
Sap from maple trees is thin, barely sweet, and as clear as melted snow in spring. The distinctive maple taste emerges only after the sap is boiled.
There’s an element of mystery to sap and its sugar content. Each fall, trees produce starch that helps protect their roots from freezing during winter. When the snow melts, water penetrates the roots and this sugared water begins circulating within the tree in preparation for the growing season.
The spring thaw causes the wood of the tree to expand, which puts the water trapped in the sap wood under pressure. If just one hole is made in the bark, the sap will run forth. This stage lasts until the tree’s buds leaf out, generally from March to April.
The ideal conditions for harvesting sap consist of a stretch of warm days with below-freezing temperatures at night.
The maple producer taps a tree by using a drill to make a hole 1 cm in diameter and 5 cm deep. A maple tree can be tapped in more than one spot. However, making multiple holes in a maple is not recommended if its trunk is less than 25 cm in diameter. After tapping the tree, the producer inserts a tap so the sap can run into a bucket.
It’s important to realize that tapping doesn’t affect the health of the tree. After the sap harvest, a long, slender vertical scar appears where the tap was. However, the outer bark is no longer alive so the hole will close up in two or three years, as the tree grows around the wound. Maples may live to be almost 200 years old.
Maple producers traditionally gathered sap by hand, using metal buckets and horse-drawn sleds that transported the sap to their sugar shacks.
Today, elaborate tubing systems connect each tree in a sugarbush, conducting sap directly to the sugar shack.
Partial sap concentration by reverse osmosis
Many maple producers use partial reverse osmosis units that let them increase the amount of sugar in the sap, thus reducing the time it needs to be boiled.
Sap is boiled in metal vats, or evaporators, until it turns into syrup. It has to be boiled the same day that it is harvested, so maple producers must keep steady fires going constantly to obtain good maple syrup. On average, it takes about 32 liters of maple sap to produce one liter of maple syrup.
Sap must be boiled to evaporate its water content and concentrate its sugar content.
As sap boils, it goes through a complex series of chemical reactions that create the unique maple syrup color and flavor.
Sap is transformed into syrup when it reaches a temperature of 104° C (219.2° F).
Before syrup is bottled or used for other products, it must be filtered to remove any impurities. There are two filtration methods, one involving gravity and felt filters and the other is a filter press operated under pressure.