Question

why butter is generally wrapped in a wet cloth if no refrigerator available

Answer 1

Butter is generally wrapped in a wet cloth if the fridgerator is available because in summer it was due to a lot of heat if no adequate coolest is available it is generally wrapped with a wet cloth

Answer 2

During summer, particularly in tropical countries like India, milk and milk products like butter, often go sour due to high temperatures. When an object is wrapped in wet cloth, the water contained in the cloth evaporates which brings down the temperature of its content.

Remember the earthen pot we used to keep at our home in olden days? That also used to give us pleasingly cold water in pre-refrigerator days on the same principle. The pot being earthen, used to be porous which allowed minute quantities of water to pilfer on its surface. That moisture evaporates thereby removing some part of the heat from the pot water.

In other words, the action mentioned by you is an age old scientific trick used by our ancestors which is still being put into practice where refrigerators are not available.