Air: Necessary for Life but Lousy for Freshness

I went to my grocer's deli for some sandwich meat and cheese the other day. The girl behind the counter was new. One of the ways I could tell was that when she handed me my packages of sliced ham and Swiss cheese, they looked like little balloons. I opened a corner of each bag and let out all the air while politely explaining to her that air and freshness were not friends. She said, “Oh, I didn't know that.” A lot of people don't.

You and I would turn up our toes pretty quickly without a supply of air. Same thing is true of the little microscopic critters that cause our food to spoil. Not all of them. Some bacteria are anaerobic, meaning they don't need air in order to survive and reproduce. Some – called facultative anaerobes – go both ways. But the little nasties that cause most food spoilage are happiest when they have a lot of air to breathe. That's why you want to give them as little as possible.

Among the many elements that assault our fresh foods in an effort to stale and spoil them, air is the biggest offender. Some foods don't like heat, others have an aversion to cold, some spoil with exposure to moisture, and some don't much care for light. But practically none of them like air. Air carries unpleasant flavors and odors to some things; it removes necessary moisture from or adds unnecessary moisture to others; it causes browning through oxidization; it makes some foods go rancid. Air acts differently on different substances but detrimentally on just about all of them.

Now wait, you say. If that's true, then why are a lot of foods, like potato chips, packaged in bags that are full of air? Well, it's not really air in there, at least not in the traditional sense. Regular air is 78% nitrogen, 21% oxygen, and 1% other inert gases. Without going into a lot of complicated chemistry, it's primarily the oxygen that causes things to go stale, so food manufacturers counter this problem by replacing the common “air” in the bag with a custom mix that has a heavier concentration of nitrogen. Try opening a nice fresh bag of chips and letting that blend of gases out. Then close the bag back up with lots of good old regular air trapped inside there and see how long the chips stay fresh. Some poor clueless individual has even mounted an online petition demanding that manufacturers stop putting air in potato chip bags. Believe me, you really don't want that to happen.

Foods that contain fats and oils – like potato chips, for example – are prone to oxidative spoilage. Oxygen causes a chemical change in fats. The short chain carbon compounds that result from these changes are acrid, nasty, and really unpalatable. Ever bite into a really stale potato chip? Yuck.

Butter is another good example of this process. If you have two working taste buds in your mouth, you can tell when butter has gone rancid or “bad.” Many people mistakenly think that temperature is the culprit, but it's really air. Temperature does play a part when it comes to long term storage. Cold retards bacterial growth. That's why you keep butter in the refrigerator or freezer. But who wants to spread rock hard butter on soft bread? So you leave a stick out on the counter and it goes “bad” before you know it. Because it needs to be kept cold, right? Not so much. It needs to be kept away from exposure to the oxidizing agents in air. You have to keep it in an airtight environment. A butter dish – especially a pretty glass one – is generally not going to do it. Some form of butter crock – often marketed under the name “Butter Bell” – is the answer. It's a two-part ceramic contraption; the butter goes in the top and an inch or two of water goes in the bottom. When the top is inserted into the bottom, the water forms an airtight seal and your butter will stay nice and fresh for several weeks without refrigeration. That's how they did it before refrigerators and the method still works.

Obviously, the best way to get rid of air is through a vacuum seal of some sort. Most foods that can be affected by microbial growth are sold in vacuum sealed packages. Many of them are in resealable packaging. Now, once a vacuum pack has been opened, you'll never get the same preservative effect unless you have a vacuum sealer of your own. But even resealable packaging is useless if you don't get out as much air as possible when you close up the package. If you zip open a fresh package of sandwich meat, take out a few slices, and then close it back up with a lot of air in it, the meat will spoil more quickly than if you take the extra few seconds required to press all the air out before you seal the package. Same thing applies to anything that was factory sealed when you bought it. Meats, cheeses, breakfast cereals, cookies, crackers, snack foods – in order for it to stay fresher longer, you've got to get that air out of there. It doesn't matter if you fold over the top or slide the zipper or press down the little seal strips if you've left air in the package. Take the time to press out as much air as possible before you seal the bag. Flatten that sucker. Well.......maybe not with potato chips, but you get the idea. You can at least flatten the top part of the chip bag. If you're really fanatical about removing air, you can take a common drinking straw and stick it in a corner of the bag and suck out the air as you seal the bag. Or you can just press. Like I said, you're not going to get a perfect vacuum seal either way. The point is to get out as much air as you can.

Air is even the culprit in food that goes bad in the freezer. Yep. Freezer burn is caused by air. If you bring home a nice steak and stick it in a bag and throw it in the freezer and come back a week later to find it looking like an ice-crusted shoe sole, it's because you left too much air in the bag.

Moisture evaporates from food at any temperature, even sub-freezing ones. And what facilitates evaporation? Ding, ding, ding! Air. In simple terms, when you've got air in a freezer bag, it gives moisture a place to go. And the water droplets that evaporate into the air trapped in the bag turn into ice crystals and you have freezer burn. The way to prevent such spoilage is to not give the water vapor any place to go. Once again, vacuum packing is the best solution, but just making sure the food is tightly wrapped and that as much air as possible is expressed from the packaging will help. If you open that factory sealed bag of frozen French fries, take a few out, and then just fold over the top and throw the bag back in the freezer, you've just frozen a bag full of air. And you've given the moisture that naturally evaporates from the potatoes a place to go and turn into ice crystals. And the next time you open the bag, it looks like a bag of ice with potatoes sticking out of it. Press that air out of there.

The best way to prevent freezer spoilage is to wrap whatever you're freezing in a tight moisture barrier of some sort – plastic wrap, aluminum foil, freezer paper – and then put the tightly wrapped food in a container from which as much air as possible has been removed. Say you got a great deal on pork chops. Take them out of the store packaging and individually wrap each one as tightly as you can. Then put the wrapped chops in a sealable plastic bag, press the air out, and seal the bag. When you take out a chop or two, remember to press the air out of the bag again before you stick it back in the freezer.

Should you use freezer bags or will regular storage bags work? Both will do the job, but freezer bags will do it a little better because they are made of slightly thicker, more puncture resistant plastic. But in a pinch, any zip top bag will do as long as you've tightly wrapped the food in a moisture barrier and gotten all the air out of the bag.

Food is too expensive to lose to unnecessary spoilage and waste. Such waste can be reduced or eliminated through proper storage, and proper storage begins by being aware of air.