Grapes are by far one of the hardest fruits to wash thoroughly. They’re always coated with that white, waxy stuff that just doesn’t come off with a regular rinse (it's called the 'bloom' and you can read more about it below).
In general, you should always rinse fruit/vegetables before eating them. Don't rinse them and then store them, because if you remove the white, waxy bloom, the exposure to moisture and air tends to make them rot faster.
The white film, called “bloom,” is something that you see on a number of soft fruits and protects the grape from things like moisture loss and decay. Produced by the grape itself, the bloom is mostly made of a waxy substance called oleanolic acid.
Yes! Frozen grapes make a delicious snack and can even be used in lieu of ice cubes to chill a glass of wine. Wash them accoding to the instructions below and then after then are completely dry you can freeze them.
The most important step is getting your grapes in the refrigerator immediately upon arriving home from grocery shopping. Grapes will stay freshest when stored at temperatures between 32 and 36 degrees Fahrenheit.