Love the new picture. That's a glass jar with a stainless steel spigot, right? If so you shouldn't have to worry much about contamination or leaching plastics. Good deal.
I'd wager that you're trying to cut your brew with more sugary juice because you're not getting enough fizz during the primary ferment. I don't brew with the continuous method because I really like the way the carbonation builds up during the secondary fermentation, plus I don't want to accustom myself to drinking that much sugar.
I do my primary ferment for seven to nine days, then a secondary ferment for usually about two days. Since most of the sugar has been eaten up during primary, I add 2oz to 3oz of an organic clear fruit juice and about a teaspoon of dry ginger per quart (or liter) before starting the secondary. The quart/liter bottles have a flip-top stopper, and I usually "burp" them every 12-24 hours during secondary just to see how it's coming along. After secondary ferment I pour the bigger bottles into 12oz screw-top bottles and because some carbonation is lost in that process, I will often let those sit out for another 12 hours before refrigerating.
I like to think that most of the sugar in the fruit juice has been consumed as it turns to carbonation, but it's difficult to know what the remaining concentration really is. My juice choice tend to be pomegranate, cranberry, or a generic organic "berry" mixture. But honestly I bet just adding a teaspoon or two of straight refined white sugar would taste the same - fizz & ginger dominates in my final beverage. The combination of a strong fizzy effervescence and that gingery snap is what I love in my Kombucha.
If you don't want to go thru that much trouble, try making up a "mocktail" (non-alcoholic cocktail) like I often do...
- 6 oz Kombucha Tea (KT)
- 2-3 leaves Fresh spearmint
- 1 Tablespoon Frozen berry mix (blue, rasp, black)
- 1 very thin slice lemon
- 1 very thin slice lime
Grab your glass. Muddle up the mint leaves with a mortar & pestle, then add to glass (or just muddle in the glass with a wooden spoon). Chop and crush down the berries, add 'em in. Squeeze the lemon & lime into the glass, toss the peel in too. Throw in the ice, pour in the KT, stir. Drink up!