14 MISC. PUBLICATION 340, U. S. DEPT. OF AGRICULTUEE 



does not always mean that grapes showing it have been rained on. 

 It frequently occurs in shipments made up of grapes picked long before 

 the rains began. Hence the recognition of it as due to rain must 

 always depend (1) on there having been rain, (2) on the presence of 

 the other symptoms described, and (3) on the absence of conditions 

 that might have brought it about without rain having fallen, such as 

 dew in the vineyard or the condensation of moisture on the fruit after 

 it is placed in the car. 



RAISINING 



The production of raisins by drying is a regular procedure in the 

 marketing of a large part of the crop from vinifera vines in California 

 and other parts of the world. But the presence of raisining in fresh 

 grapes shipped for table use is undesirable, since it damages their 

 appearance. It is also undesirable in juice grapes if the juice is to 

 be pressed from the grapes for wine making, because it reduces the 

 quantity of juice obtainable. On the other hand, if the grapes are 

 crushed and then allowed to ferment, pomace and all, some raisined 

 fruit is desirable because of its high sugar content. 



Four stages can usually be recognized in bunches where raisining 

 occurs: (1) Plump, fresh grapes that have normal color; (2) grapes 

 that are still plump but have begun to turn brown (pi. 6, B) ; (3) grapes 

 that are definitely brown all over, have lost moisture, and are becom- 

 ing flabby and soft; and (4) those that have progressed far enough in 

 the drying process to have assumed the color, taste, and physical con- 

 dition of raisins (pi. 6, A; 7, A). 



White or green varieties darken as they dry, and when found in the 

 soft, flabby condition are sometimes thought to be decayed. A cor- 

 rect diagnosis is easily made by tasting a few affected berries. 



Kaisining may be due to extremely hot weather during the harvest 

 season or to delay in removing the crop from the vines. Whether or 

 not it can develop in storage or transit is a question to which no definite 

 answer can be made. In a test with Alexandria (Muscat) grapes at 

 shipping point in California in 1934 no darkening was found in either 

 green or amber fruit after holding it in storage at 50° F. for 10 days 

 and then at room temperature for 10 days more. In transportation 

 tests made the following year 7 percent of the undiscolored berries in 

 one test and 11 percent in another became noticeably darkened after 

 14 days in an iced refrigerator car. No increase was noted in the per- 

 centage of true raisins, but evidence was obtained that grapes showing 

 some darkening when loaded had a greater tendency to continue to 

 darken in transit than those that were normal in color when loaded. 

 No data are available for other varieties grown in California. 



RHIZOPUS ROT 



(See Strawberries: Rhizopus Rot, p. 21) 



RING MILDEW 



Malaga and Alexandria (Muscat) graoes grown in California occa- 

 sionally show a brown spotting which is known as ring mildew or 

 fingerprint mildew (pi. 5, C, D). No evidence has been obtained that 

 the spotting is caused by the grape powdery mildew, or indeed by any 

 other organism; yet it keeps its name and has the appearance of being 



