Along with the lemon the brown sugar gives "sima" its (mild) taste and a bit of colour I suppose
. The raisins are an indicator: when they rise on the top, the stuff is ready to drink, that is, has gotten carbonated by slowly continuing to ferment in the cold (capped). The taste improves a bit for keeping it for a few days after that. Warning: carelessly opening a a bottle forgotten in the cellar for a couple of weeks results in an instant, sticky mess
) Done by the recipe this is very mild alcoholwise and as most of the sugar has not been converted it is also sweet so kids can have some and like it (which, I suppose, invokes fond memories in older people who have been introduced to it as kids
)