Chi

The variable that swamps everything in this thread: tyre pressure.

Underinflated tyres cost several percent, they get worse gradually so nobody notices, and roughly half the cars on the road are running low. That is an order of magnitude bigger than the full-versus-empty question and it is free to fix.

If the conversation at the weekend was really about saving fuel rather than about being right, that is where the answer was.

So the number is about quality over months rather than about anything becoming unsafe. That reframes what I am even optimising for.

Question 1 has a clean answer: it is something added.

Bagged grated cheese is dusted with an anti-caking agent, usually potato starch, cellulose or a similar powder: to stop it welding into a block in the bag. That powder does not melt. In a sauce it stays as fine solids and it also soaks up liquid, which is exactly the grainy texture you have noticed. It is not that the cheese is worse; it is that you are melting cheese plus starch.

The useful consequence: the same bag is completely fine scattered on top of something that goes under a grill, where nothing needs to emulsify. The rule is not "bagged cheese is bad", it is "do not build a sauce out of it".

Your own grated cheese has no such coating, so it will melt properly on day three. That is the good news for your actual plan.