Water Kefir is a fizzy probiotic drink. A lot of people think of it as a healthy homemade soda pop replacement. It is basically fermented sugar water. The kefir grains (which aren't grain at all, but actually yeasts and bacterias) work to eat the sugar converting it into simple sugars that have probiotics, higher vitamins (because they are made more easily digestible) including hard to get B vitamins. For a much better explanation check out this website, or google Water Kefir. There is also a Milk Kefir that you use with Raw Milk. This is not that.like these. You don't have to use swing tops. You can reuse beer bottles, if you buy extra caps and a capper, you can reuse store bought kombucha bottles or you can use another quart mason jar. I have found that the swing top bottles and the beer bottles create the most fizz. And sometimes if you use kombucha bottles they become hard to open, due to the pressure build up. Do not use plastic bottles. It's handy to have a funnel and you'll need a small strainer. Plastic is recommended, but since the grains don't stay in it long, I use metal. You want to keep your grains away from metal for the most part, I've read.
Pour a bit of your favorite juice in the bottom of each bottle. This is a cherry juice. My favorite is grape. If it is a lighter flavor juice I add a bit more (like the cherry above), grape I use a bit less. Experiment to your liking. Citrus juices are not recommended, although some people like to put a slice of lemon. Ginger also works well in kefir. You can also use fresh fruit instead of juice. Berries work excellently. Strawberry kefir is delicious!
For one quart of kefir you want to use 1/4 cup of grains and 1/4 cup of sugar. For most batches I use organic cane sugar. Sometimes I do half organic cane sugar and half succant. Kefir thrives on the succant, but it has a stronger flavor in my opinion so I don't use it as often. If your grains ever get a bit sad (they take too long to ferment, they aren't getting as bubbly, they start to get very, very small) use sucanat and or 100% pure blackstrap molasses (just a bit) to perk them back up. They need the minerals that plain white/cane sugar doesn't provide.
*** Important to note. If you need a break from your kefir or you are going out of town, just get to the step where you are about to leave them on the counter to ferment, but instead, stick them in your fridge. They will keep for weeks like this and I think you can even rescue them if you forget about them for several months. If you are planning on taking a several month break from them, you can dehydrate them. I have not done this myself, but have heard of plenty of success stories.
If you just have them in fridge storage, when you take them out, depending on how long they've been in the fridge, they may be ready to pour on juice or may need to sit out for a bit. You can tell by how fizzy and the smell once you get some practice at it. ***