38 



MISC. PUBLICATION 5 4 0, U. S. DEPT. OF AGRICULTURE 



less loss of soluble materials from the blanched material. Investiga- 

 tions of the Western Regional Research Laboratory tend to indicate, 

 however, that losses due to series blanching may be less than those 

 encountered in ordinary water blanching, but not necessarily less than 

 with steam blanching. 



Table 6. — Effects of water blanching and steam blanching on losses of vitamin C, 

 sugar, and protein from dehydrated vegetables 



Vegetable 



3-minute blanch in— 



Vitamin 

 C lost i 



Sugar 

 lost 2 



Protein 

 lost 2 





f Water 



Percent 

 49.0 

 28.0 

 38.0 

 20.0 

 46.0 

 36.0 

 32.0 

 11.0 



Percent 

 22.6 

 17.5 

 12.7 

 18.5 

 7.5 

 3.3 



Percent 



22.1 



Peas .. . _ . 



\Steam . 











(Water 



18.5 















f Water ... 









t Steam 



fWater 











Brussels sprouts 



\Steam . . . . . 















1 Data from Adam, Horner, and Stanworth (2). The carrots are reported as diced and the beans as 

 sliced and green. 



2 Data from Horner (21). 



Very largely because of differences with regard to loss of soluble 

 materials, steam blanching is generally recommended. In fact, Gov- 

 ernment specifications for most dehydrated vegetables require that the 

 product be steam-blanched. 



It is not possible to state accurately the blanching times required 

 for different products, since the time is dependent upon a large number 

 of factors that must be controlled. Among the factors that may in- 

 fluence the blanching time are the following : (1) Size of pieces. Since 

 the product should reach a temperature of at least 190° F. in the 

 center of each piece, it is obvious that the larger the piece, the longer 

 will be the time required to reach this temperature. (2) Depth to 

 which the material is loaded on the blanching trays or belt or amount 

 of material loaded into blancher. It is obvious that the greater the 

 depth of the load, or amount of load, the longer will be the time re- 

 quired for penetration of heat to the center. (3) Uniformity of heat 

 distribution in the blancher. If there are pockets or areas in the 

 blancher in which the temperature is low, a longer blanch will be re- 

 quired to compensate for the low temperatures. (4) Ability of the 

 blancher to maintain a high temperature. If the temperature should 

 drop for any reason, it is obvious that a longer blanch will be required 

 to obtain the same degree of blanch had the temperature not dropped. 

 (5) Characteristics of the raw material, such as variety and maturity 

 of the product. 



An additional factor that may influence the blanching time is 

 altitude. This factor applies to both steam and water blanchers 

 operated at atmospheric pressure in those cases where the blanching 

 temperature is specified as that of live steam and boiling water. In 

 general, the greater the altitude the lower will be the temperature 

 that can be maintained, and consequently the longer will be the blanch- 

 ing time. Variations of as much as a degree or two may occur as a 

 result of day-to-day changes in barometric pressure. The following 

 tabulation shows the effect of altitude on the average boiling point of 

 water. 



