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



alkaline waters have little effect on texture, but strong alkalinity, 

 such as is produced by adding sodium bicarbonate or sodium sulfite, 

 causes an abnormal softening of the tissue which results in some in- 

 stances in an unpleasant sliminess in the reconstituted product. Water 

 supplies high in calcium and magnesium salts are common. Such 

 water is likely to harden the skins on peas and lima beans. 



Taste and "flavor are affected only by relatively strong acids and 

 alkalies, which are not encountered in ordinary usage. 



Variation in the composition of drainage and well waters is an 

 important matter. Indeed, the lack of uniformity from day to day 

 or month to month may be a crucial difficulty in comparative testing 

 in dehydration plants and should not under any circumstance be over- 

 looked or disregarded. The cost of supplying a uniform quality of 

 water, such as ordinary distilled, may be negligible as compared with 

 the cost in time, material, and poor results obtained when tap water 

 is used. 



The size and shape of the individual pieces determine in part the 

 amount of water that a given weight of dehydrated material will im- 

 bibe, in unit time and at unit temperature. For example, from one lot 

 of carrots (fig. 71) two samples were dried, one sliced one-eighth inch, 

 the other three-sixteenths inch thick. The former slice reached its 

 original water content in approximately 3% hours and the latter after 

 16 hours at room temperature (78° F.). These results show the im- 

 portance of specific directions for home and institution use. In gen- 

 eral the thick pieces require some soaking before boiling. 



Serial Tests 



No generalization can be offered here as to the number of duplicated 

 tests that should be performed or the number of points on a rehydra- 

 tion curve that must be found. From the data presented in figure 72 

 it is obvious that single tests have little value. Figure 72 shows a set 

 of six pairs of carrot samples of one variety dried at various tempera- 

 tures until they had attained finished moistures of approximately 5.0 

 and 2.0 percent. They were sliced three-sixteenths inch thick and 

 blanched 4 minutes. The problem was to determine whether or not 

 the rate and effectiveness of rehydration had been influenced by the 

 drying conditions and to correlate these conditions with optimum 

 quality in the rehyclratecl sample. From preliminary studies it had 

 been found that good samples of carrots were soft and tender after 

 boiling 10 to 20 minutes, and also that by soaking overnight and then 

 boiling 10 to 20 minutes a plumper, smoother slice with a higher co- 

 efficient of rehydration was obtained. It seemed advisable to try 

 serial rehydration tests, in which time and temperature of rehydration 

 varied from 10 and 20 minutes of boiling, without soaking, to soaking 

 overnight (17% hours) and then boiling 10 and 20 minutes. 



As a means of determining extent to which failure to rehydrate 

 might be caused by surface hardening of the pieces, samples were 

 ground through 20-mesh sieves and then boiled without soaking for 

 10 and 20 minutes. Duplicate tests were made at each time-tem- 

 perature interval. The average drained weight from these duplicate 

 tests were used for calculating the coefficients reported in figure 72. 

 This plan gave 14 rehydration tests on each sample. 



