Put the rosehips into a pot, and add 8 cups of water. Bring to a simmer.
Simmer for about 30 minutes over low heat, then cool. I have left mine overnight before, but you don’t need to.
Strain out the rosehips.
Add the honey or sugar and stir until dissolved. (You can also just save this as rosehip syrup! This is a nice way to make another batch later– you can freeze, then dilute when you want to make another batch, quickly. Dilute the syrup with water to get a good juice flavor and consistency.)
Pour the “juice” into a sterilized or very clean demijohn, pour in your whey or sauerkraut juice and add your airlock. (I have a small swing-top container that I used for making a smaller batch than usual. An airlock fits in the top. Some people have had success with putting a balloon over the top of the demijohn with a pin hole in the top to mimic an airlock. Worth a try in a pinch!)
Let it sit for about three days, and taste it. Mine fermented pretty quickly, but there are some variables– the temperature of the room, the strength of the culture you used, etc. Taste it and let it ferment until it’s only a little sweeter than you would like it to be.
Pour it into your swing-top bottles, and store in the fridge. (The type of bottle is important, as they allow the ferment to give off some small amounts of Co2 and won’t explode.) You could leave them out at room temperature if you’d like to drink them sooner, but I usually pop them into the fridge to slow down the fermentation process.
You will want to drink them within a few weeks, or risk losing most of your Rosehip Soda to the “geyser effect.” If you’re storing it for a while, I’d just check in now and then to see what kind of pressure is building up. Your beverage will get drier, more tart and fizzier the longer you wait. It will eventually develop more of an alcohol content, too, so you might want to taste it before giving it to your kids if you’ve been storing it for a while! Enjoy!