Maple syrup is a syrup made from the sap of maple trees. In cold climates, these trees store starch in their trunks and roots before winter; the starch is then converted to sugar that rises in the sap in late winter and early spring. Maple trees are tapped by drilling holes into their trunks and collecting the sap, which is processed by heating to evaporate much of the water, leaving the concentrated syrup.
Maple syrup was first made by the Indigenous peoples of Northeastern North America. The practice was adopted by European settlers, who gradually changed production methods. Technological improvements in the 1970s further refined syrup processing. Virtually all of the world's maple syrup is produced in Canada and the United States. The Canadian province of Quebec is the largest producer, responsible for 70 per cent of the world's output; Canadian exports of maple syrup in 2016 were C$487 million (about US$360 million), with Quebec accounting for some 90 per cent of this total.[1][2]
Maple syrup is graded based on its colour and taste. Sucrose is the most prevalent sugar in maple syrup. In Canada, syrups must be made exclusively from maple sap to qualify as maple syrup and must also be at least 66 per cent sugar.[3] In the United States, a syrup must be made almost entirely from maple sap to be labelled as "maple", though states such as Vermont and New York have more restrictive definitions.
Maple syrup is often used as a condiment for pancakes, waffles, French toast, oatmeal, or porridge. It is also used as an ingredient in baking and as a sweetener or flavouring agent. Culinary experts have praised its unique flavour, although the chemistry responsible is not fully understood.[4]
Three species of maple (Acer) trees are predominantly used to produce maple syrup: the sugar maple (Acer saccharum),[5][6] the black maple (A. nigrum),[5][7] and the red maple (A. rubrum),[5][8] because of the high sugar content (roughly two to five per cent) in the sap of these species.[9] The black maple is included as a subspecies or variety in a more broadly viewed concept of A. saccharum, the sugar maple, by some botanists.[10] Of these, the red maple has a shorter season because it buds earlier than sugar and black maples, which alters the flavour of the sap.[11]
A few other species of maple are also sometimes used as sources of sap for producing maple syrup, including the box elder or Manitoba maple (Acer negundo),[5][12] the silver maple (A. saccharinum),[5][13] and the bigleaf maple (A. macrophyllum).[14] In the Southeastern United States, Florida sugar maple (Acer floridanum) is occasionally used for maple syrup production.[15]
Similar syrups may also be produced from walnut, birch, or palm trees, among other sources.[16][17][18]
Indigenous peoples living in northeastern North America were the first groups known to have produced maple syrup and maple sugar. According to Indigenous oral traditions, as well as archaeological evidence, maple tree sap was being processed into syrup long before Europeans arrived in the region.[19][20] There are no authenticated accounts of how maple syrup production and consumption began,[21] but various legends exist; one of the most popular involves maple sap being used in place of water to cook venison served to a chief.[20] Indigenous tribes developed rituals around syrup-making, celebrating the Sugar Moon (the first full moon of spring) with a Maple Dance.[22] Many aboriginal dishes replaced the salt traditional in European cuisine with maple syrup.[20]
The Algonquians recognized maple sap as a source of energy and nutrition. At the beginning of the spring thaw, they made V-shaped incisions in tree trunks; they then inserted reeds or concave pieces of bark to run the sap into clay buckets or tightly woven birch-bark baskets. The maple sap was concentrated first by leaving it exposed to the cold temperatures overnight and disposing of the layer of ice that formed on top. Following that, the sap was transported by sled to large fires where it was boiled in clay pots to produce maple syrup. Often, multiple pots were used in conjunction, with the liquid being transferred between them as it grew more concentrated. Contrary to popular belief, syrup was not typically produced by dropping heated stones into wooden bowls, especially in northeast North America where Indigenous cultures had been using clay pots for thousands of years.[23][21] However, modern and historic sources contain evidence that hot stones may have occasionally been used in the upper Midwest and Canada, where hollowed out logs and birchbark containers typically replaced clay pots.[24]
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In the early stages of European colonization in northeastern North America, local Indigenous peoples showed the arriving colonists how to tap the trunks of certain types of maples during the spring thaw to harvest the sap.[25] André Thevet, the "Royal Cosmographer of France", wrote about Jacques Cartier drinking maple sap during his Canadian voyages.[26] By 1680, European settlers and fur traders were involved in harvesting maple products.[27] However, rather than making incisions in the bark, the Europeans used the method of drilling tapholes in the trunks with augers. Prior to the 19th century, processed maple sap was used primarily as a source of concentrated sugar, in both liquid and crystallized-solid form, as cane sugar had to be imported from the West Indies.[21][22]
Maple sugaring parties typically began to operate at the start of the spring thaw in regions of woodland with sufficiently large numbers of maples.[25] Syrup makers first bored holes in the trunks, usually more than one hole per large tree; they then inserted wooden spouts into the holes and hung a wooden bucket from the protruding end of each spout to collect the sap. The buckets were commonly made by cutting cylindrical segments from a large tree trunk and then hollowing out each segment's core from one end of the cylinder, creating a seamless, watertight container.[21] Sap filled the buckets, and was then either transferred to larger holding vessels (barrels, large pots, or hollowed-out wooden logs), often mounted on sledges or wagons pulled by draft animals, or carried in buckets or other convenient containers.[28] The sap-collection buckets were returned to the spouts mounted on the trees, and the process was repeated for as long as the flow of sap remained "sweet". The specific weather conditions of the thaw period were, and still are, critical in determining the length of the sugaring season.[29] As the weather continues to warm, a maple tree's normal early spring biological process eventually alters the taste of the sap, making it unpalatable, perhaps due to an increase in amino acids.[30]
The boiling process was very time-consuming. The harvested sap was transported back to the party's base camp, where it was then poured into large vessels (usually made from metal) and boiled down to achieve the desired concentration.[21] The sap was usually transported using large barrels pulled by horses or oxen to a central collection point, where it was processed either over a fire built out in the open or inside a shelter built for that purpose (the "sugar shack").[21][31]
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Around the time of the American Civil War (1861–1865), syrup makers started using large, flat sheet metal pans as they were more efficient for boiling than heavy, rounded iron kettles, because of a greater surface area for evaporation.[31] Around this time, cane sugar replaced maple sugar as the dominant sweetener in the US; as a result, producers focused marketing efforts on maple syrup. The first evaporator, used to heat and concentrate sap, was patented in 1858. In 1872, an evaporator was developed that featured two pans and a metal arch or firebox, which greatly decreased boiling time.[21] Around 1900, producers bent the tin that formed the bottom of a pan into a series of flues, which increased the heated surface area of the pan and again decreased boiling time. Some producers also added a finishing pan, a separate batch evaporator, as a final stage in the evaporation process.[31]
Buckets began to be replaced with plastic bags, which allowed people to see at a distance how much sap had been collected. Syrup producers also began using tractors to haul vats of sap from the trees being tapped (the sugar bush) to the evaporator. Some producers adopted motor-powered tappers and metal tubing systems to convey sap from the tree to a central collection container, but these techniques were not widely used.[21] Heating methods also diversified: modern producers use wood, oil, natural gas, propane, or steam to evaporate sap.[31] Modern filtration methods were perfected to prevent contamination of the syrup.[32]
A large number of technological changes took place during the 1970s. Plastic tubing systems that had been experimental since the early part of the century were perfected, and the sap came directly from the tree to the evaporator house.[33] 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.[21]
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.[21] 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.[34] Experiments show that it may be possible to use saplings in a plantation instead of mature trees, dramatically boosting productivity per acre.[35] 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.[36]
Open pan evaporation methods have been streamlined since colonial days, but remain basically unchanged. Sap must first be collected and boiled down to obtain syrup. 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.[31][37] Syrup can be boiled entirely over one heat source or can be drawn off into smaller batches and boiled at a more controlled temperature.[38] Defoamers are often added during boiling.[39]
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).[40] The syrup is then filtered to remove precipitated "sugar sand", crystals made up largely of sugar and calcium malate.[41] These crystals are not toxic, but create a "gritty" texture in the syrup if not filtered out.[42]
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.[43] Smaller producers can also use batchwise recirculating reverse osmosis, with the most energy-efficient operation taking the sugar concentration to 25% prior to boiling.[44]
The higher the sugar content of the sap, the smaller the volume of sap is needed to obtain the same amount of syrup. To yield 1 unit of syrup, sap at 1.5 per cent sugar content will require 57 units, while sap at 3.5 per cent sugar content only needs 25 units of sap.[45] The sap's sugar content is highly variable and will fluctuate even within the same tree.[46]
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.[47] 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.[48]
Off-flavours can sometimes develop during the production of maple syrup, resulting from contaminants in the boiling apparatus (such as disinfectants), microorganisms, fermentation products, metallic can flavours, and "buddy sap", an off-flavour occurring late in the syrup season when tree budding has begun.[49][50] In some circumstances, it is possible to remove off-flavours through processing.[49][51]
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