A. nigrum Michx. f.Source: Magness et al. 1971
Maple sugar and syrup are obtained from the sap of these two species and are solely products of the United States and Canada. The Indians were making crude syrups and sugar from maple sap before the coming of white men. The preparation of maple sugar and syrup is strictly a farm industry, occurring from Kentucky northwest to Iowa, northeast to Maine and north into Canada. Native stands of these maple species are tapped to obtain the dilute juice or sap. The trees are not a cultivated crop, although competing useless trees may be removed and maple stands may be thinned to promote better growth and sugar yield. Only a small proportion of the available trees of these species are actually tapped. It is estimated that more than 200 million such trees are growing in the United States, and less than 6 million are tapped.
The tapping is done by boring a small hole (under 0.5-inch diameter) horizontally into the tree so as to penetrate through the outer or sap wood. On large trees up to four such taps may be made at one time. Tapered spouts (hollow tubes) are driven into the holes to fit tightly, and the sap flows through this tube and is collected in sap buckets. it is important to protect the buckets and contents from rain water. Tapping is done in late winter, before bud break. During periods when temperatures are above freezing at this season sap flow is quite abundant, A tap hole usuallv produces 5 to 15 gallons of sap, though much more than that is sometimes obtained. Sugar content of the sap also varies widelv, from l0 to 30°Brix or higher.
Portable tanks of various types are used to collect the sap, which is poured into the tank through strainers. An alternative method is to use pipc lines to carry the sap to the evaporation equipment.
Originally a single open kettle over a fire was used to evaporate the excess water in the sap to produce syrup. Now multiple evaporators are mainly used, the syrup being transferred as it becomes more dense. Usually 2 or 3 transfers are made. Modem evaporating pans have flues in them through which the heat from the fuel passes to speed the process and codserve fuel. For standard-density syrup, concentration is to 65.5°Brix, which is about 86 percent solids by weight. If the sap tests 2.4°Brix, 34 gallons would be required to produce one gallon of syrup.
Slow evaporation–or longer heating time–in the final stages of concentration result in a darker colored syrup. More rapid evaporation at this stage gives a lighter colored, higher grade syrup. Sensitive thermometers are used to determine when the syrup is concentrated to the standard of 65.5 Brix. The completed syrup contains solid granules, mainly calcium malate, termed sugar sand. For toable syrup these must be removed. On the farm they may be allowed to settle out or are removed by filtering. Centrifuging is efficient if available.
To produce various types of maple sugar, the syrup is further heated and additional water driven off. If heated to a boiling point of 230°F. and cooled rapidly without stirring a solid cake is formed. Stirring during cooling results in crystal formation. For fine crystals the highly supersaturated solution is seeded with fine crystals and stirred rapidly, which results in rapid formation of great numbers of fine crystals.
Numerous products, as maple cream, or butters, soft-sugar candies, maple spread, and candies utilize maple syrup or sugar. Total maple syrup production in the United States averaged approximately 1,400,000 gallons, 1961-66, inclusive. This includes that made into sugar. In addition about 800,000 gallons of syrup and 5,145,000 pounds of sugar were imported annually from Canada during those years.