I've been experimenting with not using SCOBYs when setting up cultures. I get lovely, thick, well-formed SCOBYs. I started wondering how adding a SCOBY was doing anything, since I heard about other people using the old SCOBY to make their next batch. The old SCOBY is submerged, sometimes even sitting at the bottom of the jar. The SCOBY of course is where the bacteria sit at the surface, so they can stay wet but have access to lots of oxygen. If the SCOBY isn't on the surface it's just a meaningless piece of cellulose, and that's what lots of people use rather than the active one on top.
I tried making cultures without SCOBYs. Not surprisingly, they grow SCOBYs just as quickly as the cultures with starter SCOBYs. I usually add about 10-15% kombucha and 85-90% sweet tea, and a SCOBY (or piece of one). If I make two batches side by side and give one a SCOBY and the other the same volume in extra kombucha, the one without the starter SCOBY actually brews faster and grows a new SCOBY more quickly, with no difference in 'quality' (as judged by my taste buds), just a slightly shorter brewing time. I interpret that as there being more microbes in the liquid than in the SCOBY (which is basically just permeable cellulose with a bit of liquid). I did wonder if there would be lots of bacteria in the SCOBY and more yeast in the liquid, and perhaps that is the case, but either way, there is obviously plenty of everything in the liquid.
I think using old SCOBYs is especially meaningless. You're just putting some inert byproduct into your new culture.
I tried making cultures without SCOBYs. Not surprisingly, they grow SCOBYs just as quickly as the cultures with starter SCOBYs. I usually add about 10-15% kombucha and 85-90% sweet tea, and a SCOBY (or piece of one). If I make two batches side by side and give one a SCOBY and the other the same volume in extra kombucha, the one without the starter SCOBY actually brews faster and grows a new SCOBY more quickly, with no difference in 'quality' (as judged by my taste buds), just a slightly shorter brewing time. I interpret that as there being more microbes in the liquid than in the SCOBY (which is basically just permeable cellulose with a bit of liquid). I did wonder if there would be lots of bacteria in the SCOBY and more yeast in the liquid, and perhaps that is the case, but either way, there is obviously plenty of everything in the liquid.
I think using old SCOBYs is especially meaningless. You're just putting some inert byproduct into your new culture.