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AGRICULTURE HANDBOOK 134, U.S. DEPT. OF AGRICULTURE 



contribute to its flavor — the sugar, the organ it- 

 acid salts, and even the oil, butter, or whatever 

 was used as an antifoam agent during evapora- 

 tion. An unknown number of trace materials in 

 the sirup or sugar give it "maple flavor." These 

 compounds have defied identification for many 

 years because they exist in very small amounts 

 (a few parts per million), and their chemical 

 character in many cases is so similar to carbo- 

 hydrates that separation from the sugars of the 

 sirup has been extremely difficult (123). Now 

 with the modern techniques of gas chromatog- 

 raphy and mass spectrometry, progress is being 

 made in solving the mystery of "maple flavor." 

 The flavor compounds identified can be divided 

 into two groups according to their probable 

 source. One group, possibly formed from lig- 

 neous material in the sap, contains such com- 

 pounds as vanillin, syringealdehyde, dihydro- 

 coniferyl alcohol, acetovanillone, ethylvanillin. 

 and guaiacyl acetone. A second group, most 

 likely formed by caramelization of the carbohy- 

 drates in the sap, includes acetol, methylcyclo- 

 pentenolone (cyclotene), furfural, hydroxymeth- 

 ylfurfural, isomaltol, and alpha-furonone (25, 

 116). It has been impossible to make a synthetic 

 maple flavor by combining these compounds. 

 Perhaps one or more key compounds have not 

 yet been identified. Even if all these compounds 

 were available, a proper balance of the many 

 parts of a mixture to give the desired combina- 

 tion flavor would be difficult to achieve since 

 they have not been accurately measured. 



Factors that control color and flavor are: (1) 

 Amount of fermentation products in the sap 

 (75)\ (2) pH of the boiling sap; (3) concentration 

 of the solids (sugars); (4) time of heating (time 

 necessary to evaporate sap to sirup); and (5) 

 temperature of the boiling sap (la, 150). The 

 two most important factors are the time of 

 heating and the amount of fermentation prod- 

 ucts in the sap (150). The temperature of the 

 sap under atmospheric pressure (open pan) boil- 

 ing is fixed, and nothing can be done about it. 

 Neither can anything be done about changes in 

 pH of the boiling sap. At the beginning of 

 evaporation, the natural acidity of fresh sap is 

 lost and the sap becomes alkaline. It is during 

 this alkaline phase of the pH cycle that hexose 

 sugars, if any are present, undergo alkaline 

 degi-adations. The sap then remains alkaline 



until sufficient organic acids are formed by the 

 decomposition of the sap sugars to make the 

 sap acid again. 



The longer the boiling time, the darker the 

 sirup; and, conversely, the shorter the boiling 

 time, the lighter the sirup. During evaporation, 

 the effect of the boiling-point factor increases 

 as the solids concentration of the sap increases. 

 The relation between the amount of hexose 

 sugars (invert sugar) produced during the fer- 

 mentation of the sap and the length of time the 

 sap is boiled is of the greatest importance. 

 Thus, the color and flavor of sirup made in 

 exactly the same boiling time from a series of 

 saps of equal solids concentration (Brix value) 

 but with increasing amounts of invert sugar 

 will be progressively darker and stronger. The 

 stronger maple flavor, however, is usually 

 masked by the acrid caramel flavor. Although 

 flavor and color are formed because of exo- 

 thermic chemical reactions, the amount of fla- 

 vor that can be produced is limited by the 

 concentration of the sap-soluble lignaceouslike 

 materials that are probable flavor precursors. 

 Indications are that there are sufficient of 

 these flavor percursors in sap to permit forming 

 a product that is from 15 to 30 times richer in 

 maple flavor than is commercial "pure maple 

 sirup" (15i). These precursors can be utilized to 

 increase the flavor by subjecting the sirup to 

 higher temperatures. This method is used in 

 preparing high-flavored maple products, de- 

 scribed later. 



Buddy Sap and Sirup 



As the maple tree comes out of dormancy, 

 physiological changes in the tree form constitu- 

 ents in the sap which, when boiled, give off a 

 noxious odor and impart a characteristic, un- 

 pleasant flavor to the sirup. This noxious odor 

 is most noticeable in sap obtained from trees 

 whose buds have swelled or burst during a 

 period of warm weather; and sirup made from 

 this sap is said to have buddy flavor. Due to the 

 unseasonably warm weather in 1963, buddy sap 

 was produced early in the sap season. Because 

 of this, much of the crop was not harvested in 

 some areas. Although the trees may not have 

 come far enough out of dormancy to cause the 

 buds to swell, they may have come out enough 



