There are at least 20 species of tree that can be tapped for their edible sap. And in many cases, once the sap has been reduced, a syrup can be produced. Trees in the maple (Acer spp.) family can be tapped from January to March – as long as the nights are cold and the days crisp and sunny. Birch trees (Betula spp.) however only run for a very short period of 2 to 3 weeks in mid- to end of March once the coming of Spring starts the sap flowing. Walnut trees (Juglans spp.) like a freezing cold winter and spring. Some walnut species can be tapped from autumn right through until spring.
Climate change is affecting sap production. Although some of this is hearsay, there is certainly recorded evidence that maple sap yields in southern states are dropping and that the season is starting earlier, often in December, and not lasting as long. It also affects the quality of the syrup. Higher temperatures are linked to maple syrup with higher levels of phenolics which makes the syrup darker. Phenolics are secondary metabolite defense compounds that influence the flavour of the sap.
Acer dasycarpum SILVER MAPLE (SOFT MAPLE)
Silver maple produces a good syrup but in only about half the quantity of sugar maple. So around 32 litres of sap is required to fill a large (454g) honey jar of syrup.
Acer pseudo-platanus SYCAMORE (SYCAMORE MAPLE, MOCK PLANE)
According to Sturtevant 1919, “In England, children suck the wings of the growing keys for the sake of obtaining the sweet exudation that is upon them. In the western Highlands and some parts of the Continent, the sap is fermented into wine, the trees being first tapped when just coming into leaf. From the sap, sugar may be made but not in remunerative quantities.”
Acer saccharinum SUGAR MAPLE
The most productive of the maples, around 18 litres of sap will produce a large (454g) honey jar of syrup (1919). For ease of comparison, 20 litres yields about 500 grams. In the 18th and 19th centuries, Native American’s were recorded as making a candy from the sap which was poured onto the snow to cool. That must have been some ice cream topping! A single tree can yield around 2 kilos with occasionally yields reporting around 15 kilos (33 pounds) from a single tree.
Acer rubrum RED MAPLE (SWAMP MAPLE)
Red maple produces a syrup but not more than half the quantity of sugar maple. So around 20 litres of sap will make about 250 grams of syrup.
Betula alba WHITE BIRCH (PAPER BIRCH)
“From the sap, a wine is made in Derbyshire, England, and, in 1814, the Russian soldiers near Hamburg intoxicated themselves with this fermented sap. The leaves are used in northern Europe as a substitute for tea, and the Indians of Maine make from the leaves of the American variety a tea which is relished. At certain seasons, the sap contains sugar. In Maine, the sap is sometimes collected in the spring and made into vinegar” (1919).
Betula lenta BLACK BIRCH (CHERRY BIRCH, MAHOGANY BIRCH, SWEET BIRCH)
As with white birch, the sap was occasionally made into vinegar (1919).
Betula papyrifera PAPER BIRCH
The carbohydrate concentration (glucose, fructose and sucrose to sap) has been analysed in paper birch at 0.9% compared to sugar maple which is 2-3%. So, theoretically 20 litres would make 350 grams at best.
Betula pendula SILVER BIRCH
The sap also contains sugar in the spring and can be tapped. This is the one most commonly found in the UK. In my experience, 20 litres yields around 100-150ml (80 to 120g) of syrupwhich is much lower than the reported yield of the paper birch.
Betula nigra RED BIRCH (RIVER BIRCH)
The sap also contains sugar in the spring.