all depends what ingredients they use but i very much doubt it will be like any beer. no grains will be in their recipe. they will probably make a batch of sugar n water up and chuck the vegi stuff in. it will ferment out but wont taste too good. then they could add some squash to taste when drinking but i dont think them alkie abos will bother with that .
marmite is made from the yeast after its used to brew with i believe. its just a yeast byproduct. i have viewed recipes with a little added to use as a yeast nutrient and also tomato puree too