The brown stringy things hanging from your SCOBY or floating in your kombucha are strands of yeast, a normal and harmless byproduct of the fermentation process. They are a sign of a healthy and active kombucha culture.
During kombucha fermentation, the SCOBY (Symbiotic Culture Of Bacteria and Yeast) consumes sugar and produces various acids, gases, and other compounds that give kombucha its characteristic flavor and health benefits. Yeast is a crucial component of the SCOBY, and as it multiplies and works its magic, it forms these stringy, sediment-like structures. These are simply colonies of yeast cells clumped together. They can appear brown due to the tannins from the tea used in the kombucha brewing process. The presence of these yeast strands indicates that your SCOBY is active and fermenting properly. They are completely safe to consume and do not indicate spoilage. You can filter them out if you prefer a clearer kombucha, but they are perfectly fine to drink.
If you find the yeast strands unappealing, try using a tea with fewer tannins, such as green tea, or filtering your kombucha through a cheesecloth or fine-mesh sieve before bottling. This will help remove the majority of the yeast strands and create a cleaner final product.