Why is Vegemite a concentrated solution?

Vegemite is the left overs after the beer is brewed. It's a concentrated mix of dead yeast and a little bit of liquid that is boiled off to make the paste. It's not really a solution as the yeasts do not actually dissolve.

Vegemite is a product brand name for Autolysed yeast paste. Marmite is another brand name for this paste. Autolysis means the yeast began feeding on itself, converting their cellular structures into multiple glutamic compounds. These are where it gets it's characteristic salty taste.