Nitrogen Flushing Protects and Preserves Foods

Potato chips are kept fresh by nitrogen gas.
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Americans consume a lot of processed foods every day. They're convenient and easy to transport and store. Processed foods need a lot of protection, from the processing plant to the grocery store, and to your kitchen. Plus, you may need to store them for awhile before you use them.

Dry foods are usually packaged in bags and boxes. The key to long-term preservation is removing oxygen from the containers because the oxygen exposure causes the food to deteriorate.

The fats will go rancid, discoloration of the food occurs, and the product spoils and goes to waste. There are two ways to accomplish this, either vacuum packaging or nitrogen flushing.

Vacuum Packaging

The first step in vacuum packaging is to get the food into a bag. Next, the bag is connected to a vacuum, and the air is removed, which of course, takes the oxygen along with it. The bag is sealed, and the product is ready to be labels and shipped.

Regular vacuum packaging works fine for sturdy solid foods like beef jerky and fresh meat, but it doesn't work well for foods that are delicate, like snack chips, and crackers. These foods need protection during transportation so that they won't be crushed or broken. Foods like coffee beans that have a lot of surface area and can't be squished down into an airless lump may need something more than vacuum packaging too.

Nitrogen Flushing

When you pick up a bag of snack chips, you can hear and feel the chips banging around, and it seems like there's much more air in the bag than actual chips.

 But it isn't really like the air you breathe because the package doesn't contain oxygen. All that 'air' is nitrogen gas. 

Chip and snack bags are not filled with nitrogen gas just so they look bigger. The bags are designed that way to protect the delicate foods inside from both oxygen exposure and physical damage.

The nitrogen replaces the oxygen and cushions the contents.

Unlike oxygen, nitrogen doesn't react with foods, so they stay fresher longer. That's important of course, but nitrogen doesn't affect the flavor or texture of the food, so it's perfect for food preservation. And no worries about the nitrogen gas. It's completely safe. In fact, you're exposed to nitrogen constantly because it makes up about 70 percent of the air you breathe.

How Is Nitrogen Flushing Accomplished?

First, the food is added to an open package, something like a plastic or mylar bag. Next, food manufacturers use machines that force the regular oxygen-rich air out of the bags and immediately fill them with nitrogen gas. Then, before the nitrogen has a chance to escape, a machine seals the bags tightly. The bags are placed in large boxes and shipped to grocery stores, convenience stores, and restaurants.

The nitrogen-filled packages help to protect the delicate foods inside for as long as the bag is sealed. Of course, once you open the bags, the nitrogen escapes and is replaced by regular air that's about 20 percent oxygen. That means the food inside is no longer protected and will start to deteriorate and the oils or fats will start to go rancid.

You can maintain some of the freshness by keeping the package closed with a twist tie or clip, or by placing the food in a resealable container and putting it in the fridge, but it's best to consume the food products within a short time.

Sources:

Lloyd MA, Hess SJ, Drake MA. "Effect of nitrogen flushing and storage temperature on flavor and shelf-life of whole milk powder." J Dairy Sci. 2009 Jun;92(6):2409-22.  

Marasca E, Greetham D, Herring SD, Fisk ID. "Impact of nitrogen flushing and oil choice on the progression of lipid oxidation in unwashed fried sliced potato crisps." Food Chem. 2016 May 15;199:81-6.  

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