Concentrated juice comes from pure liquid that gets drained from fruit. In order for the concentrate to be drinkable it requires the addition of water. You can easily make homemade juice concentrate sans artificial ingredients.
The method depends largely on the type of fruit you use. For example, various berries and cherries are simple: press the fruit to extract the juice and then strain it. The juice is already in concentrated form. For other types of fruits the process is slightly more involved; there are two home techniques you can use to make juice concentrate.
*Use this for lower-water content fruits like apples, pears, grapes etc.
Wash, peel and slice the fruit. If you're using grapes, they don't need to be peeled or sliced, however, you should remove the stems.
Place the fruit and sugar to taste (amount varies by fruit and preference) in a pan and add water until the fruit is submerged. Bring the water to a boil and cook for about 30 minutes or until the fruit is soft and pulpy.
Strain the liquid into another container, repeating the process until the juice is free of particulate. When ready to drink, add water to taste.
*Use for higher-water content fruits like oranges, grapefruits etc.
Express the juice from the fruit into a container. This can be done by hand squeezing or by using a juicing device. Strain the juice to remove seeds or any unwanted pulp.
Pour the juice into a narrow-necked container such as a jug. Cover and place in your freezer until the juice is completely frozen.
Remove the cover and suspend the container over another container large enough to contain the melted juice. Allow the juice to thaw to the point where the juice is beginning to drip but is still mostly contained as a block of ice. Repeat the freezing and thawing process twice more to attain a concentrated juice.