18 CIRCULAR 5 9, L T . S. DEPARTMENT OF AGRICULTURE 



The submersion methods as well as the direct- jet spray method may 

 cause the penetration of contaminated acid solution into the core of 

 the fruit and thereby may bring about decay. Even in apples with 

 closed calyx tubes deep submersion may lead to decay. 



Dipping methods in which the fruit is immersed in a cleaning- 

 solution while in boxes are open to the same objection as submersion 

 methods. 



The method whereby warm alkaline solution was used was gen- 

 erally efficient with apples. Usually a solution of soda ash of about 

 2 per cent strength was used when the residue was not too difficult to 

 remove. With heavily .sprayed lots, the addition of caustic soda 

 sufficient to make a 0.25 to 0.5 per cent solution was also added. In 

 the commercial use of this method during 1927 borax was also added 

 to the cleaning solution which was warmed to a temperature ranging 

 from 80° to 110° F. Cleaning efficiency was greater at the higher 

 temperature. 



Since the alkaline solutions are solvents for the waxy materials on 

 the surface of the apples, considerable care must be exercised in 

 making the solution strong enough to be an efficient cleaning agent 

 and yet not so caustic as to injure the fruit. A very thorough rinsing 

 with an abundance of fresh water is also essential, since the alkaline 

 materials are more difficult to wash off. 



For pears having russeted surfaces, the use of an alkaline washing 

 solution, especially when caustic soda is added, is attended with some 

 danger of injury to the skin of the fruit. 



The cleaning efficiency obtained with dipping methods as commonly 

 operated was less than that obtained with washing machines which 

 included some form of spray or flood wash when used under similar 

 conditions. This was especially true with varieties of apples that are 

 not easily cleaned or with fruit that has been subjected to spraying- 

 practices that make satisfactory cleaning difficult. 



A certain degree of agitation is essential in the dipping methods, if 

 they are to attain their greatest possible efficiency in cleaning fruit, A 

 slight turning motion in the fruit is helpful in increasing the efficiency 

 of cleaning in using most commercial washing machines of the spray 

 or flood type, but this should not be of such a character as to bruise or 

 injure the fruit. Pears are best handled by washing-machine conveyors 

 which give them a minimum of individual fruit motion. 



In the spray type of washer it has generally been found desirable 

 to have 8 to 10 pounds of solution pressure in the delivery pipes. 

 This pressure causes the solvent to flow more rapidly over the fruit, 

 whereas the flood-wash methods accomplish a similar result by pass* 

 ing a large volume of liquid over it. The pressure of the liquid 

 in the spray methods probably also removes some of the superficial 

 dust and lead arsenate. It is probable, however, that the actual 

 solution of the lead arsenate by the acid is determined largely by 

 the constant removal of the products of the reaction and the con- 

 stant renewal of the solvent against the surface of the fruit. 



A prewash of the fruit with water or very dilute acid solution 

 may assist slightly in removing some of the dust and residue from 

 fruit and will remove some of the spores from its surface. With 

 this procedure, however, there is a steady dilution of the actual 

 cleaning solution in the washer from the water carried over on the 



