I've been having fun experimenting with making my own kombucha cultures from purchased kombucha.
I have used only the plain flavor--no flavored tea or tea with juice added, etc. because I don't want to contaminate my culture.
A lot of people seem to be using mostly the sediment left at the bottom of the bottle, and that works. I've grown a couple of SCOBYs now by just leaving the last half or third of the kombucha in the bottom of the bottle and leaving it out, covered, at room temperature for a few days. The thin little SCOBYs that grew had no trouble coming out when I poured them through the neck of the bottle into a larger container.
Many bottles of the GT's kombucha have a pretty good start at a SCOBY in them already. Look in the bottoms and try to find a bottle with a pretty good chunk of almost transparent cloudy stuff--it looks like sediment at first, but the difference is that it stays all in one piece when you swirl the tea around in the bottle.
When you take off the lid, the rising bubbles will carry the little SCOBY right to the top. Wait a few minutes, and you can watch it rise slowly to float as a little film or clump of cloudy stuff at the top. If it doesn't float up, put the lid back on and gently turn the bottle upside down a couple of times, and then try again. Or you can just shake the bottle very gently a bit before you open in in the first place. Just don't shake it too hard, or you'll have an exploding bottle on your hands when you open it.
I've had success with pouring the top half of the tea, complete with the little SCOBY, into a sterilized quart jar. I then cover the jar with a natural (brown) coffee filter secured with the metal band that comes with the jars (I take out the flat metal lid, of course, and replace it with the coffee filter).
The first time I tried making kombucha from a jar of purchased kombucha, it didn't work very well. I added the baby SCOBYs from two jars of kombucha along with a cup or two of kombucha into a full-sized batch (2-3 quarts) of sweet tea in a gallon-sized jar. But the ratio of tea to kombucha and SCOBY was too much. The tea went bad before the SCOBYs grew enough to really start turning it into kombucha.
What has worked really well for me is just leaving the purchased kombucha with nothing added at room temperature for a few days. This way the SCOBY starts to develop within 2-4 days (I think I let mine go for about a week before adding anything else). I've let it culture this way for a week with a few of my experiments, and the tea was pretty sour but it made a good-looking SCOBY.
I start out with about a cup of kombucha in a quart jar and just let it work for a few days, and then tilt the jar to the side and add about a cup of cooled sweet tea. I pour it down the side of the jar to try to avoid disturbing the SCOBY too much, but the SCOBYs I've been really rough with, jostled around, played with and poured stuff on top of seem to be surviving also--they seem to be pretty sturdy little critters.
I made a new batch of sweet tea last night with 6 tea bags and 1.5 cups of sugar to 3.5 quarts of water (I boiled a little more than 2 quarts of filtered water for 10 minutes, steeped the tea for 10 minutes, dissolved the sugar in it, then added bottled spring water to cool it to room temperature more quickly--enough to make 3.5 quarts total tea).
I started a new batch with part of a fresh bottle of GTs tea, but this time I added about 1/4 of the amount of my cooled sweet tea to the prepared kombucha and the baby SCOBY from the jar. I am thinking that might give the SCOBY some extra food to give it a good start without over-diluting the culture.
The other cultures, I have had going for a week or two. To these I added new tea so that the uncultured tea was about half to three-quarters of the liquid in the jars. I'll be interested to see how quickly the various proportions work, and how they taste and look. Right now I have 5 quart jars and 1 gallon jar culturing, all at different stages, started from 5 different bottles of kombucha.
I did end up using the very old bottle of High Country Kombucha that I'd had sitting in my refrigerator for months. It worked, but I think that it has a much higher proportion of yeast in it. There is a lot of dark cloudy stuff hanging down from the SCOBY and sinking or floating suspended in the tea, and a much more yeasty smell and taste than in my GT cultures.
I've been writing notes on the edges of my coffee filters so I can keep track of which culture is which. Here are the cultures I have at the moment:
1: The culture from the SCOBY on top of the really old bottle of High Country tea.
2. Another culture from the dregs at the bottom of that same bottle. It's now in its 3rd batch of tea.
3. A culture from the last bit of tea in a bottle of GTs kombucha.
4. A hybrid baby SCOBY that grew from adding culture #2 to a GT culture that had been going slowly because I put the baby GT SCOBY in too much sweet tea.
5. A new culture from a fresh bottle of High Country.
6. A new culture from a fresh bottle of GTs.
After culture #2 got going, I added it to a slow-going GTs kombucha in a gallon-sized jar to make culture #4.
Culture #1 had TONS of yeast in it, and I tried to gently scrape off and fish out as much of the yeasty stuff as I could with a spoon when I transferred it to a new container yesterday. The kombucha from this was pretty much undrinkable, so I'll try it on my hair.
When I switched things around yesterday, I peeled the gallon-sized baby SCOBY (#4) off the quart-sized #2 SCOBY and put the smaller one into a fresh quart jar filled about 1/3 of the way with the resulting kombucha. Then I filled it almost up to the shoulders of the jar (before the narrowing) with fresh sweet tea.
I put the #4 SCOBY back into the gallon jar with a good share of the kombucha it had made and filled it up the rest of the way (slightly more than half of the total) with sweet tea.
The #3 culture has made the best kombucha tea so far, I think. I took out about half the tea it had made and replaced the amount with fresh sweet tea.
With the two new cultures I just added about 1/4 the amount of fresh tea. I put the remainder of my sweet tea in the refrigerator and plan to add it to these two new cultures in a few days once the SCOBYs get a little bigger.
Once my SCOBYs get more established, I plan to use a higher proportion of fresh tea to the cultured kombucha in some of the jars. But I also want to try at least one gallon-sized jar as a continuous-ferment kombucha culture.
I bought a glass jar with a plastic spigot at a thrift store yesterday. It didn't look like it had been used much if at all, but once I took the spigot apart there was some gunk inside it that wasn't all that easy to get off. I took it completely apart scrubbed it well and then sterilized all the parts and the jar, but I'm still not sure I trust it.
I can buy a gallon glass jar with a plastic spigot new for about $6, or one with a metal spigot for about $22. I'm trying to figure out which would be better to use for my continuous ferment.
I like the idea of a spout at the bottom of the jar so I would have to disturb the culture a little less often. But both plastic and metal spouts are going to have plastic or rubber washers, anyway, and I'm worried about the metal corroding or the plastic leaching chemicals into the kombucha. So I may just end up using a gallon-sized jar and using a spoon to hold back the SCOBY while I pour some out the top, and then gently pouring in enough fresh tea to replace what I took out.
If the continuous fermentation system works well, I'll probably end up choosing the best culture to keep in that, and going down to just one culture and maybe a backup.
But for now I'm having a lot of fun experimenting with the different cultures. Each one has its own completely unique personality, flavor and look so far. The High Country kombucha does seem to maybe have a higher yeast content than the GTs kombucha even in the fresh cultures, from what I can tell so far. But neither has cultured enough to really tell yet.