SIRUP “Sugaring” Preventable by Use of Invertase

Cane sirup and orgo sirup often “sugar,” or crystallize, and sometimes maple sirup does. The principal sugar of these three sirups, and the one which separates during crystallization, is cane sugar, the chemical name for which is sucrose. Crystallization occurs when the quantity of this sugar in the sirup is too great to dissolve in the water present at the prevailing temperature. Sucrose is less soluble in cold than in warm weather. The presence of crystals of sugar gives sirup an unsightly appearance, which often detracts from its market value. Unfortunately, the thicker sirups preferred by many people have a greater tendency to undergo crystallization than those of more common density. The crystallization of sugar also increases with the ratio of sugar to the total solid material in solution in the sirup. This ratio increases with the degree of maturity of the sorgo and sugar canes and is generally higher in first-run maple sap than in last-run sap.

If a portion of the cane sugar (sucrose) is transformed into invert sugar the tendency to crystallize is greatly reduced. Advantage may be taken of this fact to prevent crystallization, even in very thick sirups. “Invert sugar,” a mixture of the two sugars dextrose and levulose in equal parts, has about the same degree of sweetness as sucrose. The transformation of sucrose into invert sugar is called “inversion” and has practically no effect on the sweetness of sirup.

Some invert sugar is normally present in cane and sorgo juices and in maple sap. Sorgo juice contains more invert sugar than cane juice, which, in turn, contains more than maple sap. The standards of the Federal Government and of most States require that not more than 30 per cent of water be present in cane and sorgo sirups and not more than 35 per cent in maple sirup. If sirups contain no more than these specified amounts of water, crystallization of sugar does not often occur. If the sirups are evaporated to lower contents of water, however, sugar usually separates on standing, the crystallization increasing as the water content decreases. Under such conditions there is usually not enough invert sugar present to prevent crystallization and separation of sugar.

Cane and sorgo juices and maple sap contain acids which cause some inversion during evaporation. The amount of cane sugar inverted increases with the time required for evaporation, but it is not advisable to prolong evaporation for this purpose because of its harmful effect on the color and flavor of the sirup. Evaporation should be conducted just as rapidly as possible. Inversion of cane sugar can be increased by adding acid to the juice or sap, thereby preventing crystallization. This is not advisable, however, because of the effect of the acid on the flavor. Fortunately there is another method by which enough cane sugar can be inverted to prevent crystallization without affecting the flavor. This is by the use of invertase, a substance belonging to the type of substances called enzymes that are distributed in nature in both plants and animals. For instance the sugar of the nectar of flowers consists largely of cane sugar which is transformed by bees, by means of the enzyme invertase, into invert sugar, the sugar of honey.

The Bureau of Chemistry has developed a method whereby the sugaring of cane, sorgo, and maple sirups may be prevented by the use of invertase. Briefly, this method is as follows: In making cane and sorgo sirups it 1s best to add the invertase at an intermediate stage of the evaporation, say at a density corresponding to about 20° Baumé (when the sirup is about two-thirds evaporated).  Invertase is destroyed at fairly high temperatures and should not be added directly to the boiling sirup. The partially finished sirup is allowed to cool to about 150° F., the invertase is added, and the sirup is allowed to stand over night. It is then evaporated the next day to final density. Two evaporators can be used conveniently in the process. This also increases the total daily output and justifies the expense of the second evaporator. One evaporator is used for bringing the partially finished sirup, treated with invertase, to final density while the other evaporator is concentrating fresh juice to partially finished sirup. If the second evaporator does not seem desirable, a single evaporator can be used by discontinuing grinding while the partially finished sirup treated with invertase is being evaporated to final density. A tank is provided for holding the partially finished sirup during the overnight treatment with invertase.

In making maple sirup all that is necessary is the addition of the invertase to the finished sirup as soon as it is cool and at the end of a certain period, depending upon the amount of the invertase added, heating the sirup to about 185° F., so as to destroy the invertase and prevent any further action. If the maple sirup is to be held in bulk before canning, it may receive the invertase treatment during the storage period. The heating required to destroy the invertase may be gone at the time the sirup is canned.

Under certain conditions invertase can be added to finished cane and sorgo sirups instead of during evaporation. This is conveniently done in connection with the operation of a canning plant, the sirup being warmed to 150° F., invertase added, and the sirup allowed to stand for about 36 hours, after which it is heated to the required temperature for canning.

The cost of invertase is about one-half cent per gallon of cane and maple sirups and about one-fourth cent per gallon of sorgo sirup.  Full directions for using invertase, including names and addresses of manufacturers, may be obtained from the Bureau of Chemistry, United States Department of Agriculture.