Aug 3, 2010
The San Joaquin Valley experienced a prolonged period of cool, wet weather this past spring, which has delayed the development of many crops including grapes. Growers expecting to vine-dry their grapes may find it difficult to decide when to sever the canes and initiate drying; if drying is initiated too soon, raisin quality and yield will be compromised, but if drying begins too late, the fruit may not dry sufficiently before cool wet weather returns.
Recently, several studies have suggested that dry-on-vine (DOV) raisins may have higher USDA grades than raisins made from similar grapes dried on trays. The reason why drying method may affect grading is uncertain, but could be related to the effect that drying method has on the raisins’ wrinkles. Dry-on-vine raisins generally develop finer wrinkles than raisins dried on trays due to the axial vs lateral action of gravity on the drying fruit. Raisins of relatively large size and having relatively fine wrinkles will have higher USDA raisin quality scores, so the favorable wrinkling characteristics imparted by DOV might enable growers to initiate drying sooner, with fruits of lower soluble solids, than would be recommended for tray drying. If so, this would be desirable as earlier cane severance would increase the likelihood of adequately drying the grapes on the vine.
To determine the effect of soluble solids on DOV raisin yield and quality, we recently made DOV raisins from 'Fiesta' and 'Selma Pete' grapevines, with berries having a broad range of soluble solids, from 13 to 28 Brix. Then we compared raisin grades and yields as a function of berry soluble solids when drying commenced. The proportion of ‘Fiesta’ and ‘Selma Pete’ DOV raisins receiving ‘B or better’ raisin grades increased with the level of berry soluble solids. Vines having fruit with high solids also produced greater yeilds in Selma Pete.
Recently, several studies have suggested that dry-on-vine (DOV) raisins may have higher USDA grades than raisins made from similar grapes dried on trays. The reason why drying method may affect grading is uncertain, but could be related to the effect that drying method has on the raisins’ wrinkles. Dry-on-vine raisins generally develop finer wrinkles than raisins dried on trays due to the axial vs lateral action of gravity on the drying fruit. Raisins of relatively large size and having relatively fine wrinkles will have higher USDA raisin quality scores, so the favorable wrinkling characteristics imparted by DOV might enable growers to initiate drying sooner, with fruits of lower soluble solids, than would be recommended for tray drying. If so, this would be desirable as earlier cane severance would increase the likelihood of adequately drying the grapes on the vine.
To determine the effect of soluble solids on DOV raisin yield and quality, we recently made DOV raisins from 'Fiesta' and 'Selma Pete' grapevines, with berries having a broad range of soluble solids, from 13 to 28 Brix. Then we compared raisin grades and yields as a function of berry soluble solids when drying commenced. The proportion of ‘Fiesta’ and ‘Selma Pete’ DOV raisins receiving ‘B or better’ raisin grades increased with the level of berry soluble solids. Vines having fruit with high solids also produced greater yeilds in Selma Pete.
Effect of severing the canes of ‘Selma Pete’ grapevines on different dates on berry fresh wt, soluble solids (SS), titratable acidity (TA), brix:acid ratio, and raisin yield, grades, and moisture, Parlier Calif., 2007.
|
|
Berry |
Raisin |
|||||
|
Severance date |
Weight (g) |
SS (Brix) |
TA (g/100 ml) |
Yield (kg) |
‘B and better’ (%) |
‘Substandard’ (%) |
Moisture (%) |
|
9 July |
1.8 |
16.9 d |
1.06 a |
5.4 b |
56.9 b |
9.3 a |
11.37 |
|
16 July |
1.9 |
18.3 c |
0.90 b |
6.0 b |
65.4 b |
4.5 b |
12.76 |
|
27 July |
1.8 |
20.7 b |
0.78 c |
6.1 b |
84.2 a |
2.8 bc |
11.89 |
|
3 August |
1.9 |
22.4 a |
0.65 d |
7.8 a |
88.6 a |
2.5 bc |
12.41 |
|
8 August |
1.8 |
23.0 a |
0.64 d |
8.2 a |
92.0 a |
1.9 c |
12.77 |
