I contacted a Finnish ex-colleague, and she said she was making sima as we spoke. She uses 1/3 cane sugar, 1/3 white sugar and 1/3 brown sugar, plus lime and ginger. She doesn't like honey in it. Apparently the raisins are very important, I assume for the flavor. She uses plain baker's yeast, most often the simple dried stuff. She stores the closed bottles five days to a week, so the sima can become fizzy. She's never had any exploding bottles (the fact that she brings it up herself is a bit scary), but added that some people leave the bottles half open so superfluous CO2 can escape.