Raisins are fresh grapes that have been dried and hydrated. Good quality raisins are full and elastic in shape and have a sticky sweet taste. Also, good quality raisins have non-crystallizing and non-acidic fructose. So how to make good quality raisins in the process of drying grapes? Grapes are rich in fiber and sugar. And the raisin drying process is also the process of ripening grapes. This is the process of converting polysaccharides into monosaccharides by the action of biological enzymes, while preserving as much as possible the original quality of the grapes. This results in a better sweetness of the raisins.
Two different ways of making raisins
The optimal temperature for the conversion of the internal sugars into simple sugars during the drying process is 55-60 degrees. There are two ways of processing raisins: natural drying and using a grape drying machine. The natural drying time is long and the temperature cannot be controlled, which does not meet the needs of large-scale production. The grape dryer, on the other hand, can precisely control the drying temperature and humidity in the drying process. On the other hand, the dryer has the advantages of low operating cost and high efficiency. It is an indispensable machine necessary for modern production.
Product features of grapes drying machine
The grape dryer is professional drying equipment composed of an air energy heat pump dryer, convection air circulation system, temperature and humidity intelligent control system, drying room, and so on. It has good heating and heat preservation, ventilation, and water dispersal equipment. It also has very good sanitary conditions. The drying host absorbs the heat in the air and forms hot air through the compressor. Then it is evenly blown into the drying room through the convection fan. The sensor inside the dry grapes making machine can record the temperature and humidity. The drying temperature and drying time are then controlled.
Selecting high-quality grapes for raisins
We need to choose grapes with bright colors, thin skin and thick flesh, suitable ripeness, and sugar content above 20 percent. Then clean them and put them in the grape dryer trays. Only good quality grapes can be used to obtain good quality raisins.
Temperature control of the grapes drying machine
- The initial temperature is set between 40-50 degrees Celsius for 2 hours. The purpose of this operation is to encourage the evaporation of moisture from the grape skins.
- Mid-term mass dehydration: increase the temperature to 55 degrees Celsius for 10 hours. The dehydration rate of the grapes at this point is about 70 percent.
- Deep drying: the temperature is increased to 60 degrees Celsius. The humidity is set to 55% for 10 hours.
- Finally, the temperature is controlled at 55 degrees Celsius and the baking time is 5 hours. At this point, the moisture content of the grapes is below 12%.
At this point, the raisins are not discolored and the flesh is soft. The grapes are dry and no juice is oozing out. When a handful of raisins is squeezed and released, the grains will quickly disperse. This means that the dryness is appropriate. We can see that the white raisins have a small amount of sugar frosting on the outside. After removing the frosting, the color is crystal green and transparent. The red raisins also have a slightly frosted appearance. After removing the frosting, the color is translucent purple. The water content is less than 15%.
Grapes contain a lot of water and usually, 4 pounds of grapes yield 1 pound of raisins. The dehydration rate of grapes is about 70%. Because the outer skin of the grapes is easily broken, care should be taken to place them gently when loading the tray of the grapes drying machine. Do not over squeeze them either.