Air is the stuff of life, but there are occasions and places where its presence, particularly its oxygen component, can create some problems. While oxygen is what sustains life on our lovely planet, its presence in the ambient air also promotes the process of spoilage in foods, starting from staling to molding and rotting.

A simple example: Researchers have found that snack foods like potato chips keep fresher in their plastic bags, with the air pressed out and the bag rolled up tightly, then sealed with a clip or rubber band. The chips remain even fresher this way than having them transferred to a tightly lidded hard container. Why? Because you can press out most of the air from the flexible bag as you keep using the content, unlike in a rigid jar. You should do the same when you store food in a resealable storage or freezer bag – get the air out.

You may wonder though that when you bought the chip bag, it did look rather puffed up with “air.” That, however, was not really oxygen-laden air, but an inert gas like nitrogen that does not react with the food. That is what happens, too, when you want to conserve the quality of a good wine in a partially used bottle. You either expel the air with a vacuum pump or fill the empty space on top with an inert nonreactive gas. Of course, you have the simpler option of transferring the leftover to a smaller bottle so there won’t be any dead air on top.

The principle applies to some cooking methods as well. For example, when you want to sweat some tender vegetables, or some thinly cut skinless, boneless chicken breast slices, you put them on a lightly greased nonstick pan and put the lid on. Well, the lid cannot not really hug the veggies or chicken; under the dome, there is a whole lot of air that may not be allowing the process to work in the best way.

Here is how you can minimize the “dead” air: Cut a piece of parchment paper to fit the saute pan, crinkle it a little bit and press it on top of the food, making sure the edges are snug. Its advantage is that you can cook the veggies and more in their own juices with a minimum of water or oil. Take care not to burn your fingers though when placing the parchment.

(To cut the parchment “lid,” take a square piece slightly bigger than the pan diameter, fold into quarters, fold it into a triangle with the sharp point on the folded sides, then fold the triangle again and cut the big end with scissors so the length of the triangle roughly equals the pan radius. Spread out and fit.)

The same principle can also be utilized when marinating meat or poultry. Place the meat and the marinade ingredients, including some kind of acid, such as lemon juice or Worcestershire sauce, into a suitable plastic bag, press out as much air as you can, knead the meat to cover it completely with the marinade and quickly seal the bag. (A bag with a slider tab works quicker and better here.) A vacuum of sorts is created and the marinade hugs the meat, allowing better penetration into its pores.

The ultimate for this process, of course, is the electric vacuum sealer machine. Although I would take some of the manufacturers’ hypes for this gadget with a large pinch of salt, the principle is science-based, and foods stored in those sealed bags will certainly stay fresh longer, if properly stored. I have it on my “wish list,” but my wife Kaisari loves to flaunt a Blondie comic strip clipping in my face. Blondie has to go out to eat because she has so many gadgets on the kitchen counter that she has no room to prepare any food. Let’s see, come New Year!

NOTES FROM OUR KITCHEN

Many products that are sold in plastic bags now come with a resealable zip top. You cut a thin strip off the top, often marked, and a resealable strip is revealed. The trick in getting the most out of this, however, is to expel the “dead air” first. This is how I do it: Push the remaining product to the bottom, lay the bag on the counter, press out the air and smooth the two sides flat. Quickly seal the bag. The resulting vacuum will keep the sides pressed together. Folding the flap snug on the food and securing it with a rubber band will help keep the vacuum intact.