Table grape quality standards vary between countries. Many have been established as a result of local preference, taste and tradition. Maintaining high sugars and a juicy berry by manipulating the time of maturity is important for marketability.
Table grape berries must be of good external quality and attractive appearance to meet the market specifications.
The major external quality parameters of grape berries include color, even size, skin firmness, pulp stability, and strength of attachment to the bunch stalk.
The internal quality of table grape is of big importance. The desired level of sweetness is a matter of personal taste and preference. Sweetness of berry is expressed as the Sugar/Acid ratio. A measure of the sugar in the grape or Total Soluble Solids (TSS) content is usually obtained from assessing the oBrix of the fruit.
Application of the right amount of nutrients is the major crop management practice required to produce high quality table grape.
Crop Nutrition and Table Grape Quality
Supply of sufficient amount of macronutrients (N, P, and K) can improve table grape quality. Nitrogen is needed to produce better quality berries, because it enhances growth and development of crop. Application of N fertilizer resulted in higher sugar content of berries. Too much nitrogen, however, can lead to soft table grapes at harvest.
Potassium is a key component of nucleic acids and lipids. Thus it enhances growth and development that can increase quality of table grape. K plays the central role during transportation of photosynthetic products to support growth and development processes. Potassium increases berry size and evenness and it is also applied to improve skin color. Application of K fertilizer results in increase of sugar/acid ratio of grape berries.
Deficiency of secondary nutrients (calcium and magnesium) can negatively affect quality of table grape. Calcium is a key component of cell walls maintaining the membrane structure and also directly influences regulation of enzyme systems, phyto-hormone activities, and nutrient uptake. Post-harvest berry quality is specifically influenced by Ca nutrition. It is very important to maintain sufficient level of Ca in berry skin via Ca applications to the vine throughout the season and/or Ca sprays targeted during fruit development. Calcium sprays directly on the fruit, especially late in the season during fruit maturity, are important to improve strength of skin, and storage and handling characteristics.
Application of sufficient amount of micro nutrients is resulted in better growth and development of table grape, because micro nutrients deficiency can limit growth and development of berries. Boron enhances germination of pollen and fruit set. Application of boron fertilizer resulted in increase of sugar content.
Iron is essentially required for early leaf production and photosynthesis to ensure better berry development and quality. Supply of sufficient amount of Fe fertilizer resulted in increase of sugar content.
Zinc is involved in process of chloroplast development, thus it is essential for improvement of grape quality. Zinc fertilizer application resulted in increase of sugar content and reduction of post-harvest weight loss .