VEGETABLE AND FRUIT DEHYDRATION 45 



tions are more readily oxidized by air than are those at lower pH, 

 so that important amounts may be converted to inactive sulfate. In 

 the absence of complete information it seems best to use a mixture 

 of the two salts which will give a solution in the range of pH 7 to 8. 

 A convenient proportion consists of 3 parts by weight of sodium 

 sulfite to 1 part of the metabisulfite, which yields a solution of ap- 

 proximately pH 7.2. If desired the cheaper metabisulfite can be used 

 and the correct pH achieved by addition of soda ash. 



Hard waters cause precipitation of the highly insoluble calcium sul- 

 fite, which results in a milky appearance of the solution and upon accu- 

 mulation may cause clogging of spray jets. This precipitation may be 

 effectively inhibited by dissolving sodium hexametaphosphate (Cal- 

 gon) in the water to give a concentration of 5 p. p. m. prior to addi- 

 tion of the sulfite salts. The sulfite salts dissolve somewhat more 

 slowly in the presence of the phosphate and a large excess is to be 

 avoided because of its potentially unfavorable tenderizing action on 

 the cabbage. 



Reasonable caution should be exercised in handling sulfite solu- 

 tions to avoid contamination with metals such as iron and copper, 

 since these catalyze the oxidative conversion to inactive sulfate. Con- 

 tact with air should be minimized, especially with solutions of high 

 pH. If a solution is held more than a few hours it should be mixed, 

 sampled, and rechecked for sulfite content and ref ortified, if necessary, 

 before use. 



Corrosion of metal trays will not be serious, provided solutions of 

 pH 7 or higher are used. Tinned trays must be kept well coated; 

 otherwise cabbage coming in contact with exposed iron will be seri- 

 ously stained as a result of the relative positions of tin and iron in 

 the electrochemical series. Galvanized-iron trays are less likely to 

 cause staining of the product, since the zinc is more active than the 

 iron and hence soluble iron does not reach the cabbage. Cloths over 

 the tray screens have been tried to avoid staining and to facilitate 

 removal of the dried product without excessive fragmentation. Un- 

 fortunately, although the cloths are very helpful in detraying opera- 

 tions, they do not work satisfactorily when sulfite is used. Metal 

 trays can be treated with a light coat of mineral oil to avoid sticking 

 of the dried cabbage. 



In plants equipped with cabinet blanchers sulfiting can be carried 

 out by dipping baskets of the raw shredded material in a tank of sul- 

 fite solution. If dipped cold it is necessary to use a solution of 0.5 

 percent as S0 2 or greater to obtain the desired uptake. The cabbage 

 should remain immersed a minimum of 15 seconds, should be removed 

 and drained another 15 seconds, and then dipped in or sprayed with 

 fresh water for 5 seconds. Then it is spread on trays and blanched 

 in the usual way. Varieties of cabbage may be expected to show 

 considerable variation in absorption of sulfite from cold solutions; 

 therefore trials must be made with different sulfite concentrations on 

 each new lot of cabbage. Perhaps a more satisfactory procedure is 

 to dip the raw cabbage in a hot (180°-190° F.) sulfite solution for 5 

 seconds, drain briefly, dip momentarily in fresh water, and then spread 

 on the trays and blanch. Lower concentrations of sulfite can be 

 used when the solution is applied hot — 0.2 to 0.4 percent as S0 2 

 ordinarily being adequate. 



Dipping of cabbage after blanching is not satisfoctory because of 



