Grapes can most definitely be juiced and there are a number of ways to go about doing this. You will first want to start off by going down to your local grocery store and getting some grapes, either red or white. Make sure that you thoroughly clean the grapes so as not to leave any remnants of pesticides or other harmful chemicals on them. After you have done this you will be able to start mashing the grapes. Put all of the grapes that you have into a large bowl and mash them together and thoroughly as possible with the help of a potato masher.
After you have mashed all of the grapes together, you will be able to cook them. Just make sure to remove all of the stems and clean the mashed grapes as best you can. Then you will have to put them into a large pot, adding enough water to where all of the grapes are covered. Put the heat on medium to high until it has started to boil. Once it has reached the boiling point, you will want to turn down the heat until it has reached a slow simmer which you will want to keep going for about 10 minutes. Keep in mind that you will be occasionally stirring as the pot is simmering. After this step is done you will need to strain and empty the grape mixture and pour into a pitcher for serving.