My husband is something of a guacamole connoisseur. When good avocados can be found in our decidedly non-tropical state, he scoops them up and works on perfecting his guacamole technique. So I've also spent some time trying to make his guacamole last. In the rare instances we don't polish off the bowl, it seems a terrible shame to waste an ounce of that good green stuff. But my efforts to keep guacamole green and fresh overnight have always failed — until now. I've discovered a simple, foolproof, and easy way to keep guacamole green and delicious — and no, it doesn't involve avocado pits or extra lime juice. Want to see how I do it? Guacamole is easy to make, but there are many reasons you might want to keep guacamole beyond its usual hourlong window of freshness. Maybe you made too much and want to save the leftovers, or you want to make a big batch ahead of time for a party. I've seen many ideas for keeping guacamole fresh — Keep the avocado pit in the bowl! Press plastic wrap on top! Use more lime! — but none of them have ever worked for me. Invariably, the top of the guacamole turns brown, and I have to scrape at least an inch off to get to the good stuff below. (There's a reason, by the way, that plastic wrap doesn't work well. In the past, plastic wrap was made out of materials that didn't allow air through. But the most common material now for plastic wrap is more porous and lets air pass through — oxidizing the guacamole and turning it brown.) This method, on the other hand, works perfectly every time and doesn't involve plastic or extra lime juice. I like a precise balance of lime to avocado in my guac, and I don't want to drench the guacamole in juice to keep it fresh. This method is easy and cheap, and you can use it with any kind of guacamole. All you do is cover the guacamole with a thin layer of water. OK, you say, this sounds weird — maybe even gross. Water on the guacamole? But water is a perfect barrier against oxygen, and since guacamole is dense, a little liquid won't water it down. I pour in a small amount of water to cover the top of the guacamole and refrigerate it for up to three days. After I take it out and pour off the water, I stir up the guacamole and the texture is no different than when it was made. In fact, I like the taste of guac after it has sat in the fridge overnight; I find the cilantro and onion flavors are blended better.