When it comes to plastic-bag storage, there are a lot of good reasons to remove as much air as possible. Marinating in an air-free plastic bag helps better distribute marinades around food. Excess air causes oxidation that can develop into off flavors or promote spoilage. Air pockets can exacerbate freezer burn in the freezer and slow down sous vide cooking. Removing that air is simple to do with a vacuum sealer, but what if you don't own one or don't want to use the expensive bags for a relatively simple storage or cooking task? Here's a quick, easy, inexpensive option called the water displacement method. All you need is a zipper-lock bag and a tub or pot of water.