Prepare your grapes. Place the grapes into the colander, and wash them with cool water. Check the grapes, and remove any spoiled ones. Remove all the stems.
Fill the 4-quart pot with water, and bring to a boil. Place the grapes into the water for 30 seconds, and then remove them. This process cracks the skins of the grapes and helps them dry more easily.
Fill the large bowl with 2 quarts of cool water and 2 tsp. citric acid. Stir the ingredients well.
Transfer the boiled grapes to the large bowl, and stir them around in the water for 10 minutes. Treating the grapes in the citric acid solution improves the quality of the raisins.
Drain the raisins, and place them onto the trays of the food dehydrator in a single layer.
Stack the trays inside the dehydrator. Generally, you will set the temperature to between 120 to 140 degrees F and turn it on; however, consult the directions for your dehydrator to find the appropriate temperature.
Let the grapes dehydrate for at least 24 hours. Check the grapes after 24 hours to see if they look like raisins. If they still look moist, continue dehydrating them, checking on them every hour or two until they look completely shriveled and there is no moisture in the middle of the grape.
Remove the raisins from the dehydrator, and leave the raisins sitting on the trays for about one hour to cool.
Transfer the raisins to the plastic container, and seal the container. You should have about 1 lb. of raisins that will keep indefinitely at room temperature.