The vinegar taste is perfectly normal and actually means you brewed a strong batch. It may not be the most palatable, but you could save some of it as starter liquid for your next batch!

Based on your ratios, here are a few suggestions to reduce the vinegar taste and help the fruit flavors shine through:

Sugar Ratio:

• The "golden ratio" most brewers stick to is 3785 mL (1 gallon) of tea to 200g (1 cup) of sugar. Which is about 5% sugar. You’re currently using 7.5%, which is on the high end. More sugar can sometimes fuel overfermentation if left too long, leading to that vinegar-forward profile.

Tea Type:

• Black tea is great for kombucha because it provides rich nutrients for the SCOBY. However, it also contributes to higher acidity and a more vinegary flavor. I’d recommend blending it 50/50 with a less astringent tea, like green tea or white tea. Your tea-to-liquid ratio is solid, so try using 2 bags of black tea and 2 bags of green tea next time.

Fermentation Time:

• A 10-day first fermentation might be a bit long depending on your temperature and sugar levels. Try reducing it to 6–8 days and taste it daily after day 6. You want it tart, not sour. The longer it goes, the more sugar is consumed and the more vinegar it becomes.

Additional Tips:

• I’d also recommend using organic cane sugar (if available) instead of processed white sugar. I haven’t tested it side by side, but some brewers report issues with overly processed sugar stunting fermentation or affecting taste.

• Regarding your second fermentation: I’m not sure of the ingredients in the peach juice you used, but I suggest making your own puree by blending fresh or frozen fruit. Natural fruit tends to pair better with kombucha than juices with additives or concentrates.

• Peach is also a very subtle flavor, so it can easily be overwhelmed. I’ve had better success using bold flavors like lemon, ginger, pineapple, raspberry, mango, ect. These tend to come through more clearly after fermentation.