A: A rotten egg smell comes from sulfur. The presence of sulfur may be:
- A product of nitrogen from the tea
- From the water source
- Another thread to read on kombucha and sulfur can be found here
- According to beer brewing sites, sulfur smells in beer may be due to byproducts of certain yeasts, yeast autolysis (yeast cannibalism), or bacterial infection
- The sulfur smell goes away in beer over time according to this thread and FAQ 5.43.
According to the threads here and here, it appears that the kombucha is still safe to drink even if it smells like sulfur/rotten eggs. However, if you don't feel good after you drink it, stop!
What can you do?
- If you think the sulfur smells are due to your water source, consider using a water filter or upgrading your current water filter.
- Let your kombucha age for longer periods of time before you drink it to see if the sulfur smells decrease over time.
- If you think the sulfur smells are due to certain yeasts in your kombucha, try favoring the bacteria in your brew.
- Try cleaning all of your equipment and make sure you practice proper sanitation techniques.
- Try starting over with a new SCOBY.