Why does sugar start to stink in the canister?

maybe your sugar isnt totally sealed. make sure that your canister is well sealed to prevent moisture from entering the canister. sugar absorbs moisture from air fast and a veery good moisture retainer. the reason why it stinks is because bacteria and molds already grew on your sugar. note: there was an increased moisture content in you sugar, that would trigger the growth of these contaminants. bacteria and molds are hydrophilic, meaning they love water, they grow on water, and they love foods with high water/ moisture content.