Rough Wines are those in which an excess of tannin causes decided astringency. They usually contain pigment, but not much alcohol. Some clarets belong with this group.

As a rule, these wines are not available for general dietetic or invalid use, and are mainly employed to add to other wines to aid in their preservation and otherwise alter them, although they are sometimes drunk by peasants in the countries in which they are produced.

Concentrated Wines

Attempts to concentrate wines by heat evaporation of the water contained in them result in the loss of the ingredients which furnish "bouquet" or "aroma," and which are more volatile than the alcohol. A process has been devised in France by which concentration is secured by cold without this loss. In congealing to ice the water does not include the volatile ingredients of the wine. The wine is submitted to a temperature below freezing, the ice meanwhile being mechanically broken into minute particles, which are then separated by a centrifugal machine. The result is a wine composed of uncongealed concentrate and condensed to from 60 to 80 per cent of its original bulk, thereby improving its capacity for preservation and greatly lessening cost of storage and transportation. The same ingenious process has been successfully applied to milk and fruit juices. Upon addition of water the original bulk and degree of flavour is restored.

Raisin Wine

An inferior quality of wine is made by restoring the water of the grapes which has been lost by drying them into raisins. Wine is now sometimes made in France from raisins dried in California.