Here's the recipe for artificial nectar (syrup):
Use one part ordinary white cane sugar to four parts water.
It's not necessary to boil the water. The microorganisms that cause fermentation don't come from the water; they are transported to the feeder on hummingbird bills.
Store unused syrup in the refrigerator for up to two weeks.
This mixture approximates the average sucrose content (about 21%) of the flowers favored by North American hummingbirds, without being so sweet it attracts too many insects.