The paper-covered bottle of Lea and Perrin’s Worcestershire sauce in the door of the refrigerator is ubiquitous in the kitchens of my friends and family. It was just always there, although for the life of me I never remembered anyone buying it, and it was never on the grocery list. It was as if it just appeared, fully formed, there between the large bottle of Heinz ketchup and the parade of salad dressing bottles, since no one in the family likes the same dressing at any one time.

My dad used it almost exclusively as an addition to his homemade Thousand Island, my mom used it in the famous ketchup, butter and Worcestershire sauce she made to top whole roasted beef tenderloins, and my grandmother reached for it when she was doctoring things like soups, stews, sauces, or salads. If she felt a dish was missing a certain something, a dash of murky brown stuff often did just the trick.

But what is that certain something that Worcestershire sauce provides? What is in it? Why does it appear to be effectively inert and immune to spoilage? Why is it so awkwardly spelled and hard to pronounce?

The sauce was invented by John Lea and William Perrins in the 1830s, in Worcester (pronounced Wooster) England. The super-secret formulation is based on anchovies, and contains other things like vinegars, onions, spices, tamarind, molasses and “flavourings” which have been believed over the years to be everything from lemon to pickles to soy sauce. Lea and Perrins actually thought the original formulation was a total disaster, but not wanting to be wasteful, they dumped the stuff into a barrel and stashed it in the cellar of their pharmacy. About a year and a half passed before they decided to do a clean out to make room in storage in the basement, and when they opened the casks, found that the mixture had fermented. In a good way. The flavors—all of them in your face intense eighteen months earlier—had mellowed and melded into a sauce they could put their name on. And the name of their town.

Its shelf life is a result of that aging process. As a fermented product, the sauce stays at its best for over three years after opening as long as you keep it refrigerated, and while it is safe for much longer than that, apparently the quality does begin to degrade a bit. But as long as it doesn’t smell “off” or show mold, it is safe to consume.

So essentially, Worcestershire sauce, with all of its anchovy base, is a British version of fish sauce, which dates all the way back to the Romans who fermented casks of rotting fish to make garum, which was their version of ketchup, and probably why they lost their empire. But this raises the question: In this day and age of global cookery, can you use it instead of fish sauce in recipes?

The basic answer is yes. While Lea and Perrins added a bunch of other stuff to their sauce to sweeten it up and mellow it out for a British palate, fundamentally, the umami bomb that punches up your Caesar salad or deepens your bloody mary can also sub in for fish sauces in many recipes. USUALLY. If the dish is particularly fish-sauce-forward, I’d be a little careful, but when measured in teaspoons or dashes, you are probably fine. So the next time you go to make your famous Thai chicken salad only to find that the bottle of Red Boat is empty, reach for that paper wrapped bottle. You know the one. It’s right on the door of your fridge between the ketchup and the salad dressings.