It isn't necessary to add fruit juice to the mixture listed above. When I was teaching Molecular Biology (and Genetics) I always had dozens, if not hundreds, of fruit fly cultures so I do have a bit of experience with Drosophila
One thing that you have to keep in mind, however, is that DIY
media are susceptible to the growth of bacteria and occasionally mites so you should subculture your flies frequently (every two weeks or so). It might be easier, if you can find it, to purchase one of the commercially-available fruit fly media which generally come in dry form (simply add water) and are very easy to use. Carolina Biological Supply sells one called 4-24 which I had excellent results with.
Hope this helps a bit