It is nutrition that brings us out of ketosis. When we ingest any nutrition the body expects us to provide more and will take it as a sign that we have taken over again and stop breaking down stores and creating ketones to provide for itself. Also digestion does not start in the stomach but in the mouth, as soon as we taste anything the taste receptors send messages to the brain which then relays the message to the heart which will divert blood and energy to the digestion system. This is certainly not desirable while fasting. And continuing to taste things while fasting is very likely to continue the cravings also!