By Robert L. Wolke
Wednesday, May 23, 2007
So you buy a package of ground beef to make hamburgers, and when you begin to form it into patties -- arrrrgh! The meat inside is brown! It looked so nice and red in the supermarket. Is the meat spoiled? Are they spraying the surface with a dye to make it look fresher than it is?
No and no -- not unless it smells bad. Your best tool for detecting spoiled meat is not your eye, but your nose. Meat spoilage is caused either by microbes, which turn it putrid, or by oxidation of the fat to rancid-smelling aldehydes. Without risking your life by asking the meat monger if you may smell the meat, you just can't tell if it is spoiled.
(Here's a vital point: Even beyond the spoiling of meat by microbes and rancidity, any meat, regardless of color or odor, could still be contaminated with pathogenic bacteria such as E. coli if it has not been handled properly. That's not what I'm talking about here.)
Different colors of beef are simply different forms of the same pigment, myoglobin, a chameleon-like chemical that can be purple, red or brown, depending on its environment. The myoglobin in freshly cut, raw "red meat" is in the form of deoxymyoglobin, which is a dark, purplish-red color. On exposure to air it turns into bright red oxymyoglobin, the color we love to see in our meat as a putative indication of freshness. But inside a package of ground meat, oxygen is unavailable, and after a few days, most of the myoglobin turns into its metmyoglobin form, which is a grayish brown. It may still be perfectly good meat.
Retailers control the oxygen exposure by covering the package with a plastic film that, while blocking out microbes, allows just enough oxygen penetration to keep at least the meat's surface a nice, red oxymyoglobin color. That's the most commonly used packaging method. But perversely, myoglobin can also turn into brown metmyoglobin from too long an exposure to air. That's how meat left out too long gets "old."
Another widely used method is to seal the meat while in its red oxymyoglobin form in a gas-tight package containing not air, but a mixture of gases that have no effect on myoglobin: usually nitrogen and carbon dioxide. Variations of this so-called "modified atmosphere packaging" have been in use for the past 50 years or so.
The new kid on the block is a modified atmosphere of nitrogen and carbon dioxide containing a small amount of carbon monoxide. Yes, the same carbon monoxide that can asphyxiate you in a closed garage with your car's motor running -- but only if you breathe enough of it. It converts the myoglobin in meat into yet another form, the cherry-red carboxymyoglobin. It's a slightly darker red than oxymyoglobin, but it still shouts "fresh!" to the color-obsessed consumer.
Many Giant Food and Stop & Shop markets in the Washington area introduced their version of this technology, the "New Smarter Package," on May 11. Inside the packages of ground beef, all the air has been replaced by a mixture of nitrogen and carbon dioxide, along with less than 0.4 percent carbon monoxide, the maximum amount accepted by the U.S. Department of Agriculture and the Food and Drug Administration for this application.
In a handout to its customers, Giant says the carbon monoxide treatment "preserves" or "extends freshness" and "maintains . . . quality." But the words "freshness" and "quality" have no precise meanings; what carbon monoxide does is preserve color.
Then there's the ambiguous term "shelf life." No food suddenly becomes lethal the day after its use-by date. The date merely reflects the retailer's best judgment of the latest point at which it will still be wholesome, tasty and appealing to most consumers -- "fresh" or "high quality," if you will. Nevertheless, the absence of oxygen in Giant's packaging does make longer shelf life possible by eliminating discoloration from long-term contact with air.
Why all the fuss about the color of ground beef when color doesn't necessarily indicate freshness? To the consumer, it's pure psychology: Brown meat just doesn't look appetizing. To the retailer, it's a matter of profit: Meat that doesn't look good won't sell and must be marked down or discarded. And to the cynic, carbon monoxide could be used to cover up old, gray meat. Hence, the use of carbon monoxide as a meat cosmetic is surrounded by controversy. But what new food treatment isn't?
Note that carbon monoxide keeps the meat from turning brown, not from actually spoiling. The government requires that carbon monoxide-treated meat be labeled with a "use or freeze by" date. Most retailers use "use by" labels anyway, regardless of packaging method.
So when you buy the ground beef for your cookout this weekend, try to forget about color -- you're going to turn it brown by cooking it anyway, aren't you? -- and check the "use or freeze by" or "use by" date. If you trusted your meat market before, you can trust it now.
Robert L. Wolke, author of "What Einstein Told His Cook: Kitchen Science Explained" (W.W. Norton, 2002), can be reached firstname.lastname@example.org.