How to prevent a baby scoby from forming in bottled kombucha

Pasteurisation would reduce viable cell count in your kombucha which is undesirable.

Refrigeration, as I just recently discovered, only slows the growth of the scoby but it would give you enough time to keep the liquid clear. Given enough time (>3 months in my case), you will see growth at 3C.

Whether it is a single or double ferment, there is really no difference unless your substrate is very different in the second fermentation. The yeast species are responsible for the fizz while bacteria like G.Xylinus is responsible for the formation of the cellulose mat you want to control. I have not yet looked into what makes G.Xylinus thrive, but even in a scoby there has to be some conditions that favour yeasts over bacteria, whether it is a pH threshold or nitrogen or some other micro nutrient.

You might want to experiment with it. What I do notice is that old scoby kept at low temperatures are less capable of producing gas, which suggests that the yeast population is harmed by high acidity or high acidity at low temperature.

G.Xylinus and other bacteria feed on ethanol from yeast to produce acids (primarily acetic and lactic). So, you might want to try a removing the new growth and rebottling without any further sugar addition.

Agitation also prevents mat formation but you will still find sediments and "scum" suspended in the liquid. If that is acceptable, you can just shade the bottles periodically to disrupt the mat.

The best ways to reduce scoby formation are filtration and refrigeration. Once the scoby is removed there are still active yeast and bacteria in the kombucha. Filtration down to a small enough micron level will remove most of the yeast, which are larger, preventing both continuous fermentation(into ethanol) and the formation of scoby. The bacteria will still be present which comprises most of the desirable probiotic content. This might allow the ph to continue to decrease, becoming more acidic, but if refrigerated, this too will be quite slow or nearly imperceptible.

When folks suggest using packaged kombucha as a starter, it has be left out in a warm space long enough for the yeast to build back up and then for the scoby mat for reform, before adding new sugar and tea.

How about using Cascade or nothern brewer cone hopps for flavor ? Let batch ferment to 3.0 acidity. Remove scoby. Add hops then let batch sit in fridge for 7 days. Prime, bottle. My thinking is the acid and oils from the hops would prevent a booger snot scoby from forming in bottles.