Maple syrup was first made and used by the indigenous peoples of North America, dating back hundreds of years. From simple methods used by the Algonquian Indians through Colonists, maple syrup production process has evolved. Buckets hanging on trees have been replace by miles of plastic tubing and vacuum pumps to take the the sap came directly from the tree to the evaporator house.
It still takes a lot of sap to make maple syrup. One tap on one tree will produce approximately 10 gallons of sap (in a typical year, it does vary from year to year) which will boil down to make about one quart of maple syrup. That's a 40 to 1 ratio of sap to syrup! That's right, it takes about 40 gallons of sap to make 1 gallon of maple syrup. The higher the sugar content of the sap, the smaller the volume of sap is needed to obtain the same amount of syrup. 57 units of sap with 1.5 percent sugar content will yield 1 unit of syrup, but only 25 units of sap with a 3.5 percent sugar content are needed to obtain one unit of syrup. The sap's sugar content is highly variable and will fluctuate even within the same tree.
Not all trees produce sweet, edible, tasty sap in sufficient quantities to make a syrup! Maple syrup is usually made from the xylem sap of sugar maples (Acer saccharum) which is also known as the hard maple, rock maple, sweet maple and black maple. But maple syrup can also be made from the sap of red maple and black maple trees. It can even be made from other maple species, such as the Bigleaf Maple in the Pacific Northwest.
These trees are "tapped" meaning a hollow tube is inserted into a drilled hole. How many times you can tap a single tree is calculated based on the tree’s diameter, health and growth rate. The maple tree must be at least 8 to 10 inches in diameter. Larger diameter trees can have more taps inserted ; basically 1 more per each additional 20 cm of tree trunk diameter; up to a maximum of three taps per tree and season. Done this way, the tapping does not adversely affect the growth of the maple trees.
The season starts when temperature rise above freezing and maple trees buds start to open and leaves appear. The season can start as early as January 1st and run to as late as the beginning of May, but the typical season is from February through mid-April.
The first sap of the year is always diluted, so it has to be cooked down further to reach the optimal 66.5 percent sugar. Too little sugar and it could start to mold, too high and the sugar could crystallize. That means early, initially weak sap ends up as even darker and more concentrated syrup to reach that proper percentage. It becomes the rich black-brown of a harsh Italian espresso. When nearly finished and just before bottling, the syrup is run through a filter to extract silty minerals that cloud the molasses-colored sweet stuff.
Plastic tubing is connected to the taps and run to vacuum pumps and collection tanks.
Vacuum pumps were added to the tubing systems, and preheaters were developed to recycle heat lost in the steam. Producers developed reverse-osmosis machines to take a portion of water out of the sap before it was boiled, increasing processing efficiency.
Improvements in tubing and vacuum pumps, new filtering techniques, "supercharged" preheaters, and better storage containers have since been developed. Research continues on pest control and improved woodlot management. In 2009, researchers at the University of Vermont unveiled a new type of tap that prevents backflow of sap into the tree, reducing bacterial contamination and preventing the tree from attempting to heal the bore hole. Experiments show that it may be possible to use saplings in a plantation instead of mature trees, dramatically boosting productivity per acre. As a result of the smaller tree diameter, milder diurnal temperature swings are needed for the tree to freeze and thaw, which enables sap production in milder climatic conditions outside of northeastern North America.
After harvesting in the maple woods, the sap is transported to a sugar house where it boils down to become real maple syrup. During cooking, storage tank pipes feed sap to a long and narrow ridged pan called an evaporator. As it boils, water evaporates and becomes denser and sweeter. Sap boils until it reaches the density of maple syrup. About 40 liters (10.5 gallons) of sap boil down to one liter (about .25 gallons or one quart) of pure maple syrup. For other maple products – butter, taffy, or sugar – the sweet syrup is further boiled in the evaporator to the temperature necessary to produce the different types of maple products. After evaporation, the finished products get bottled or canned, and are shipped to their final destinations.
Open pan evaporation methods have been streamlined since colonial days, but remain basically unchanged. Sap must first be collected and boiled down to obtain pure syrup without chemical agents or preservatives. Maple syrup is made by boiling between 20 and 50 volumes of sap (depending on its concentration) over an open fire until 1 volume of syrup is obtained, usually at a temperature 4.1 °C (7.4 °F) over the boiling point of water. As the boiling point of water varies with changes in air pressure the correct value for pure water is determined at the place where the syrup is being produced, each time evaporation is begun and periodically throughout the day. Syrup can be boiled entirely over one heat source or can be drawn off into smaller batches and boiled at a more controlled temperature.
Boiling the syrup is a tightly controlled process, which ensures appropriate sugar content. Syrup boiled too long will eventually crystallize, whereas under-boiled syrup will be watery, and will quickly spoil. The finished syrup has a density of 66° on the Brix scale (a hydrometric scale used to measure sugar solutions).
In addition to open pan evaporation methods, many large producers use the more fuel efficient reverse osmosis procedure to separate the water from the sap. Smaller producers can also use batchwise recirculating reverse osmosis, with the most energy-efficient operation taking the sugar concentration to 25% prior to boiling.
The syrup is then filtered to remove precipitated "sugar sand", which is sediment made up largely of sugar and calcium malate. These crystals are not toxic, but create a unpleasant gritty texture in the syrup if they are not filtered out.
The filtered syrup is graded and packaged while still hot, usually at a temperature of 82 °C (180 °F) or greater. The containers are turned over after being sealed to sterilize the cap with the hot syrup. Packages can be made of metal, glass, or coated plastic, depending on volume and target market. The syrup can also be heated longer and further processed to create a variety of other maple products, including maple sugar, maple butter or cream, and maple candy or taffy.