Can one use raw sugar in making tea for kombucha? Most recipes recommend refined sugar, but I wonder if it is for any particular reason.
Absolutely you can. I typically use a Turbinado sugar when making mine because it's what I buy in bulk and because I like the robust flavor.
In my searches, I did come across this article indicating that you shouldn't use such raw sugars because they're more difficult for the scoby to digest, but as long as you start with a healthy one you should be fine. Maybe just don't go as far as using a brown sugar, or something very raw like muscovado.
I brew Kombucha and use Organic but refined sugar. This helps especially when cooler temps come and the brewing time slows down because of it. The harder you make food available for the scoby the slower the brew time. With a slower brew time comes a higher risk of contamination.
Remember that the sugar isn't for you, it's to feed the scoby If you flavor your tea in a second ferment, I would recommend adding your raw sugars then if it's for flavor alone. The refined sugars should be pretty much depleted during the first ferment.