Watermelon is a hard fruit to make wine out of. The flavor is very volitile and does not fare well through primary fermentation. Also the wine is very thin and watery. Often it needs a second flavoring ingredient to improve the overall wine. When making these kinds of wines it is also important to get good watermelons. Don't use the big oval watermelons that we are all used to. Get the smaller round ones that are dark green. Those will pack more flavor. Here is a simple watermelon wine recipe you can try:
1 gallon
1 gallon of fresh pressed watermelon.
3 cups dried hibiscus petals (these are what I am talking about hibiscus
1/4 cup chopped raisins
Juice of 1 lemon and 1 orange
4 cups sugar
1/2 tsp acid blend
1 Camden tablet
1 tsp yeast nutrient
Yeast (lalvin RC-212)
Add all the ingredients lack your watermelon juice your jug/jar. Then top up with the juice. You should have plenty left over. Freeze that juice and save it for when you rack to secondary for topping off. Watermelon juice spoils easily so that is why I say freeze the leftover. I really like hibiscus so I included that as the secondary flavor ingredient. But feel free to substitute that with anything like: 2 ripe bananas, 1/4lb dried elderberries, 2lb strawberries or 2 peaches. After adding the Camden tablet make sure to pitch the yeast after 24 hours. Mix the wine twice daily for the first week. When there is 1/4" - 1/2" of settled lees rack to new jug/jar and top up with juice. Let it clear completely and rack again. Now add Camden and sorbate, after 12 hours top up with any remaining juice and sweeten with sugar to taste.