If you syrup is possibley fermenting then try:
Place the syrup in a sauce pan. Set on stove.
Bring some water to a boil separately.
Rinse your syrup bottle well, scrubbing if possible then fill with hot, hot water; scrub the cap as well and place in a bowl of hot water. Then after the bottle is hot, pour off that water and fill with boiling water then pour this off carefully and then fill again with hot water; do the same with the bottle lid. Set aside while you do the next thing:
Over low heat, bring to barely boiling and reduce heat while you empty the bottle filled as above. Pour in the hot syrup and then cap the bottle (it's going to be hot, so again, be careful). Best to place this in the refrigerator, but make sure you place the hot bottle on a clean, DRY towel, to avoid any themal shock that may break your syrup.
AND, Thank you for the chinchona bark!