MAPLE SIRUP PRODUCERS MANUAL 



67 



The nitrogenous matter constitutes only a 

 small part of the total solids (88).'' Expressed as 

 nitrogen, the sap contains only 0.0013 percent 

 and the sirup 0.06 percent. The sap does not 

 contain any free amino acids except late in the 

 sap-flow season. Nitrogen occurs only in the 

 form of peptides. Whether the nitrogenous mat- 

 ter enters into the formation of maple color or 

 flavor is an open question. An increase in free 

 amino acids is associated with the development 

 of "buddy sap." 



FORMATION OF TRIOSES 

 FROM SUCROSE 



HYDROLYSIS OF SUCROSE 



C|2 HjjO,, 

 (SUCROSE) 



FISSION OF HEXOSES 



(HEXOSES) 

 ► Cg HiaOe + CsHjOg 

 (GLUCOSE) (FRUCTOSE) 



(.olor anti Flavor 



Maple sap as it comes from the tree is a 

 sterile, ciystal-clear liquid with a sweet taste. 

 None of the brown color or flavor that we 

 associate with maple sirup is in the sap. This is 

 easily demonstrated by collecting sap asepti- 

 cally, freezing it, and then freeze-drying it. The 

 solid obtained is white or very light yellow and 

 has only a sweet taste. The typical color and 

 flavor of maple sirup are the result of chemical 

 reactions, involving certain substances in the 

 sap, brought about by heat as the sap boils 

 (H8). Since at least one of the products of the 

 reaction is the brown color, it is known as a 

 browning reaction. Neither the exact nature of 

 this reaction nor the identity of the reacting 

 substances is known. Indications are that one 

 or more of the 6 sugars or their degradation 

 products and one or more of the 12 organic 

 acids in maple sap are involved in the browning 

 reaction. 



Experimental evidence indicates that the 

 color and flavor of maple sirup are related to 

 triose sugar {52-5J,, 118-120, 122, 155). These 

 sugars are not constituents of sap when it 

 comes from the tree but are formed as a result 

 of the two reactions shown in chart 14. Evi- 

 dence also indicates that the phenolic ligninlike 

 substances of maple sap are intermediate in the 

 flavor reactions and may account for the speci- 

 ficity of maple flavor (117). 



The amount of invert hexose sugars is di- 

 rectly proportional to the amount of fermenta- 

 tion that has occurred. The first reaction is the 

 bacterial or enzymatic hydrolysis of the sucrose 

 to form invert sugar, a mixture of fructose and 



GUUCIC ACID 



TRIOSE n 



ACETOL 



'Also unpublished data of Eastern Regional Research 

 Center. 



Chart li. — Chemical reactions showing the formation of 

 trioses from the sucrose of sap. In the first reaction, 1 

 molecule of sucrose is hydrolyzed by enzymes to yield 2 

 molecules of hexose sugars. In the second reaction, 

 these hexoses are broken by alkaline fission into 

 trioses. 



dextrose (chart 14). The second reaction is the 

 alkaline degradation of the fructose and dex- 

 trose to trioses (98). The second reaction occurs 

 while the sap is boiling in the sap pan, where 

 the alkalinity of the sap reaches a pH of 8 to 9. 

 These trioses are highly active chemically. 

 They can combine with themselves to form 

 color compounds, and they can react with other 

 substances in the sap (such as organic acids) to 

 form the maple flavor substances (79). 



Experiments have established that up to a 

 point the amount of color formed is proportional 

 to the amount of flavor formed. This makes it 

 possible to evaluate flavor in terms of color, a 

 measurable quantity. When the point is 

 reached at which the background flavor "cara- 

 mel" begins to be noticeable, this relation no 

 longer holds. 



The identity of the compounds responsible for 

 the flavor of maple has proved to be elusive. 

 Certainly all the components of maple sirup 



