What is the purpose of yeast extract in a Cumberland pie?

[DettolObsessed]

I have found a recipe for vegetarian Cumberland pie which says to add yeast extract? Do I have to do this and what does this do exactly? Does it help it rise? I only ever use it when making dough/bread.

Yeast extract is Marmite. It will add savoury flavour to the sauce.

@EskewedBeef looks like I need more sleep! I realise now it is marmite lol. I was thinking of dried yeast

Yeast extract is a form of glutamate (think msg) so it enhances the flavours.

@TheSandgroper that makes more sense now! And just wondering if you know : would red split lentils be OK to use instead of green lentils as I don't have of the latter? Thank you :)

Red split need less cooking and soften to a paste. Green keep their shape and texture better. Without reading the whole recipe, it's hard to see what the impact would be.
Does it ask for cooked lentils, or dried?

Stick to green lentils and soak them overnight to speed up cooking the next day. Red lentils add very little in terms of texture or flavour. Add marmite and also brown sauce. Gravy can be bistro as that's made with soya.