Most mold spores cannot survive and grow after being heated. This means that you can effectively clean your sweet tea of contaminants by pasturizing it before it gets added to your healthy batch and SCOBY. So what temperature will keep your pellicle safe and sound? Check out this research on the effects of pasteurization on mold spores conducted by the US Department of agriculture.
From the Journal of Agricultural Research vol. vi, No., available here: https://naldc.nal.usda.gov/download/IND43965604/PDF
The study finds that two methods of pasteurizing were effective against mold in milk. It would follow that Kombucha tea exposed to molds of the same varieties would also be pasteurized and clean of mold contaminants at the same temperatures.
Mold Control Method: Holder Pasteurizing - Hold temperature at 145F for 30 minutes.
- Result - killed the mold spores of every species investigated, except those of Aspergillus repens, A. ftavus, and A. fumigatus were killed.
Mold Control Method: Flash Pasteurizing at 175F for 30 seconds.
- Result - This method killed all the spores that survived the holder method in the USDA experiment. This method should be our preferred method for sanitizing kombucha brewing vessels and sweet tea on its way to becoming kombucha.
So why is boiling your tea and adding sugar when it is hot not enough? Well, it is if that is all you add… but what I used to do was take some cool water or ice cubes to immediately cool down my hot tea so that I could add in my Scoby and kombucha starter. If you watch youtube videos about kombucha, this is a common method, but if that cool water, or ice has even a single mold spore that has not been heated then BAM! We have deadly kombucha mold contamination and you may have to throw out the batch.
Here is my new method: Boil everything (no more cool water mix-in), carefully add it to by brewing vessel at pasteurization temperatures, then affix my kombucha bonnet (an invention that I will share about more in the future) and allow the batch to cool before I add the SCOBY and starter at a safe temperature (below 80F).
Boiling temperature water should be adequate to kill these spores in your hot, sweetened tea however that does not mean that all of your brewing equipment is clean. If you use 175F and 30 seconds as safe assumption for killing kombucha mold, then I think you will be a happy booch brewer.