Here’s what you need to do to make homemade grape juice: 1. Gather your grapes and wash them. Destemming the grapes is also a necessary step. Note that a pound of grapes will only yield a cup of juice, so make sure to prepare more if you wish to extract more juice. 2. Using a potato masher, start mashing the grapes in a bowl. Make sure that you smash every fruit to extract the most juice. 3. Cook the grapes. This will serve as the pasteurization stage. This will ensure that no bacteria will contaminate the juice once you put them in jars. 4. Strain the mixture using a cheesecloth. It may not drain immediately, so you need to wait for a few hours to complete the straining. 5. Place the filtered juice in clean jars. Make sure that no contaminant will spoil the juice. Air exposure will also call for fermentation and cause the liquid to turn sour. Make sure the jars are sealed properly.