Anyone ferments knows the problems of fruit flies, they just love kombucha, kefir and fermenting vegetables. Covering your brew with a good tight weave cloth can help to keep the little critters out of your brew but how do you keep them away.
Well.... It's crazy and we have absolutley no scientific evidence to back this up but we use this method and it works. That's all we can say.
Place between 4 and 5 pennies in a bag of water (we like the zip lock bags as they are easier to seal but any clear plastic bag works). hang the bag somewhere near the area you don't want the flies in and you will find that it keeps them at bay! Cheap, Easy and effective.
Another option is to place a few drops of orange oil in a bottle top or similar and place somewhere near your ferment.
Fruit flies and other insects do not like the smell and stay away. You will find that you need to refresh the oil every couple of days (also ensure that it cannot be eaten by pets/children).