Add spruce tips to a bowl of cold water and swirl around to clean. Remove the brown sheaths that cover the tips and strain.
Add spruce tips, lime slice, a slice of candied or fresh ginger, syrup, and 2 cups of water to a sterilized quart-sized mason jar.
Use a cocktail muddler or similar object to smash the ingredients to release their oils and extracts. Cover with a coffee filter and keep in place with a rubber band, or use a fermenting lid and airlock.
Place in a sunny window and stir daily until the mixture becomes fizzy and bubbly (about 4 days).
Once the fermentation is active, strain and discard the solids. Pour soda into flip-top bottles using a strainer and funnel. Leave at least a one-inch headspace at the top.
Ferment another day or two at room temperature, then refrigerate to halt fermentation. Enjoy chilled.
Notes
One way to identify a spruce tree is by its papery cones. The cones always point down when mature.
If you have access to a blue spruce, use it; the tips have an even better flavor!
You can technically start the fermentation in a flip-top bottle; however, spruce tips are harder to fit into the opening of the bottle. For this reason, I recommend starting the fermentation in a mason jar, then transferring to a flip-top bottle before refrigerating to halt fermentation.
If you find your fermentation is stuck (not progressing), especially when fermenting during cooler weather, try adding a pinch of either baker's yeast or champagne yeast for more reliable fermentation.
Use young tips only—bright green and tender, usually harvested in early spring.
Avoid brown, old, or resin-heavy needles (bitter and tough).
Keep a sterilized container to avoid bacteria buildup or mold.