The Effects of Harvest Date on Thompson Seedless Grapes and Raisins. I. Fruit Composition, Characteristics, and Yield

Abstract

A three-year study was conducted on the influence of harvest date on Thompson Seedless grape and raisin composition, yield, and quality. Five weekly harvests (2 years) and three weekly harvests (1 year) were performed during August and September. Fruit soluble solids as degrees Brix increased steadily during the harvest period at an average rate of 0.111° Brix per day. Berry volume and weight increased until a cessation of berry growth in September week 1 or 2. Fresh fruit yield was not significantly affected by harvest date, but raisin yield increased weekly until September week 2 and then declined. This raisin yield increase peaked one week later than did berry volume and weight and was attributed to increased SS and the accompanying lowered drying ratios. A subsequent drop in raisin yield in September week 3 was attributed to bunch rot and berry shatter losses. Fresh fruit and raisin TA declined constantly throughout the harvest period. However, raisin reducing sugar increases did not correspond well to fruit maturation rates as measured by other indices. Airstream sorter raisin grades improved with harvest date, but less so at the later harvests. This was attributed to the discontinuance of berry growth, although °Brix increased during the same period. Optimum harvest in this study occurred in September week 2, when considering the raisin yield and quality parameters studied here.