DEVELOPMENTS IN THE PRODUCTION OF TABLE GRAPES, WINE AND RAISINS IN TROPICAL REGIONS OF THE WORLD

In less than 50 years grape production in the tropics has changed from being somewhat of a horticultural curiosity to grapevines becoming the most widely grown temperate fruit in the tropics. Currently world production is over 3 million tonnes annually, with India producing more than a million tonnes and Brazil just under this figure each year. Other tropical producers include Yemen 163,000, Peru 136,000, Thailand 40,000, Colombia 19,000, Tanzania 14,000 and Venezuela 11,500 tonnes. Grapes are also produced in the tropical part of Mexico and Saudi Arabia, while many other tropical countries produce small amounts for local consumption. Many different climates exist within the tropics resulting from variations in temperature, humidity, elevation and in the amount and distribution of the rainfall. Those best suited to growing ever-green vines and producing grapes have average minimum temperatures above 15°C and a reliable dry period of at least 3 months during which bunch formation and ripening occurs. In both the dry and wet tropics, the growth and cropping cycle of the vine can be manipulated to extend from 5 to 12 months by a combination of pruning, modifying vine water status and the judicious use of chemical regulators. In the tropics overhead trellises, which separate bunches from the vine canopy and reduce bunch rotting, are the most common form of vine training. Some elevated areas within the tropics have cold periods that induce leaf fall and in these areas the growth cycle of the vine is climate controlled and not able to be manipulated. Initially grape vines were cultivated in the tropics for the production of table grapes and this is still their main end use. With their capacity to produce more than one crop per year grapevines can provide massive yields of nutritious fresh fruit at times of the year when supplies of tropical fruits are limited. New developments in this area include the growing of an increased range of seedless varieties and the selection and breeding of new clones and varieties better suited to the tropics. A further innovation has been the use of plastic shelters and plastic-houses with open sides to, shield the vines from rain, reduce the incidence of bunch rots and slightly modify ripening times. The adoption of post harvest techniques originally developed for grapes from temperate areas has been of major importance for tropical grapes. These involve fumigating the grapes with gaseous and slow release sulphur dioxide papers combined with storage at temperatures just above zero. These treatments greatly extend the shelf life of tropical grapes and allow them to be transported to distant markets. A relatively new development has been the use of tropical grapes for the production of both wine and dried raisins. Good wine is now produced in the slightly elevated, wet tropical areas of northern and eastern Thailand, from both the Shiraz and Chenin Blanc varieties. Grapes from the larger crop that ripens in the cooler low rainfall months are of better quality and have less disease than those from the monsoon crop. In a region with a somewhat similar climate, the Deccan Plateau of South India, a range of winemaking varieties are now being grown and cropped once per year, with the grapes being used exclusively for wine production. Good wine is also made from grapes, from vines grown with irrigation and cropped twice per year, in dry tropical areas of both Venezuela (Carora) and Brazil (San Francisco Valley). As with virtually all wine grapes grown in hot areas it is essential to supplement the ferments with tartaric acid to provide an appropriate acid balance to the wine. Raisin production in tropical areas of high humidity represents perhaps the ultimate challenge for tropical grapes; however, this problem has largely been solved in South India using techniques developed in Australia for producing raisins rather than drying them on paper on the ground. In this scheme of things, the Thomson Seedless (Sultana) grapes are dried on wire netting racks with roofs that protect them from the rain, after treating them with emulsions of fatty acids (mainly ethyl oleate) and potassium carbonate that hasten drying and lead to the production of light-brown coloured raisins. It is clear that tropical grape production is now a major world industry and the grapes are able to be utilized for fresh eating, wine and raisin production.