What is the definition of Ex40a?

Let's crack this joke: 'Ex40A' is like the secret ingredient in a recipe you can't find, but you know it's there because every time you reach for it, your coffee machine goes haywire. Imagine this: "Just when I thought my life was getting better, I decided to use ex40A in my morning latte, and now the espresso machine is trying to make a sandwich instead of brewing coffee." Talk about an unexpected culinary adventure!