You can store it in the fridge for up to 3 days in an airtight container. The sauce will set once it's cool into a gel consistency. It will melt when you add it to stir fry recipes. If you plan on storing your sauce for longer, leave out the cornstarch and add it into the stock mixture right before adding it to your stir fry. The reason for this is that cornstarch can lose its thickening power overtime and you can end up with a thinned out sauce.