Ah Marmite, looks and smells like road tar, but tastes great.
Or was that vegemite?
Marmite is like Coco Cola - the recipe is a trade secret.
There is a explanation of the process at
Farmers haul off tons of the stuff from breweries to use as
animal feed. So there's no reason to believe the sediment at
the bottom of a fermenter would harm you. Just put some on a
cracker (or on your finger) and see how it tastes.