JLove98905 wrote:
>
> What's the key to getting good stiff whipped cream?

Making it just before it's used rather than making it far
in advance and storing it.

> And what causes it to fall flat in the fridge?

Consider the cans. They make the foam the second before
it is used. Now consider the tubs and read the ingredients.
To keep the foam intact they use a miasma of chemicals
most folks can't pronounce.

You could add all sorts of chemcials to keep the foam,
but the better solution is just-in-time manufacturing.
Make it just before it is used.