Preserving egg yolks

Intact yolks if possible

Here's something to keep in mind: whole, or intact, yolks keep much better than if they're punctured, or liquid.
This is because the thin film that forms them, the membrane, also protects them from the outside, and prevents them from drying out.
So, as long as possible, keep them in their intact form, even if in your next recipe you'll have to crack them to incorporate them. It's best to do this at the last minute.

The enemy of yolks: dryness

The simplest and most natural way to chill yolks is to put them in a ramekin (or other small container), and place it in the fridge.

But there are two small errors here: yolks fear dryness, and as the membrane is very fragile and thin, it will quickly dry out and stick, especially if left in the open air, and even more so if left in the cold, which tends to dry everything out.

Well-preserved yolks

So how do you keep your yolks in good condition?
You just need to do 2 things:

1) Put 1 teaspoon of neutral oil or even water in the bottom of the container before the yolks, then pour in the yolks.

This will prevent them from drying out on contact with the container and sticking to the bottom.

2) Wrap the container with the yolks at all costs, or use a container with a lid, to isolate them from the air as much as possible.

Don't worry either, if you get one or more yolks punctured, it's no big deal, just a little less easy to handle, as the liquid yolks are very thick and sticky, and you'll have a bit of trouble emptying the container completely without loss (a maryse will be almost indispensable).

To sum up: try to keep your yolks intact, in a filmed or closed container, over a teaspoon of oil or water to prevent them from sticking.