I normally make this cordial in small batches so it is consumed quickly. I cannot tell you if it lasts more than a couple of weeks as it never does in our house. If you wish to make larger batches you will either need to add more sugar or properly heat treat the cordial for storage. I have on occasion made larger batches and heat treated them for storage. This has worked well. To serve, pour the desired amount into a glass and top up with cold mineral water. Add ice and enjoy! I used seven large grapefruit to produce one litre of juice.