Hi G, you can definitely double the ingredients as long as your jars are big enough to hold double. I like my jars to have plenty of extra room so the liquid doesn’t splash out when I move them. 🙂

Hi G, You can actually drink that leftover bit after the first fermentation, although it won’t be fizzy or flavored. I usually just add it to another bottle for second fermentation even though it won’t fill the bottle all the way. I hate to waste any too, so I just make it work 🙂 As for water kefir being keto friendly, I did a little bit of research and it looks like it can work for the keto diet. The recipes I found use real fruit instead of fruit juice for the second fermentation, so that might be something to try. Berries, melons, and even peaches seem to be good options. Just keep in mind that the sugar in the first ferment is for the kefir grains, not you. Virtually none of that sugar will be left after the grains consume it, so I don’t think you have to worry about the sugar content in the first ferment.