Why Does Beef Turn Green? The Science Behind This Color Change

You reach into the fridge to grab some leftover roast beef expecting to see those familiar red and brown hues. But when you unwrap it the beef looks…green? That bright, unnatural green color can seem off-putting. Is your beef still safe to eat? And what causes this transformation in the first place? Read on to learn why beef sometimes turns green and when it’s okay to eat it or throw it out.

What Causes Beef to Turn Green?

The green color change in beef occurs due to a pigment called metmyoglobin. Myoglobin is a protein responsible for the distinctive red color of raw beef. As beef is cooked, the myoglobin changes to a tan or brown pigment called oxymyoglobin.

But when beef is exposed to air particularly when raw or not fully cooked the myoglobin can oxidize into metmyoglobin, which has a greenish-gray color. This chemical reaction happens more readily at cooler refrigerator temperatures.

Some factors that encourage meat to turn green include:

• Improper storage like leaving it uncovered in the fridge
• Allowing cooked beef to remain in contact with raw beef juices
• Repeated freeze-thaw cycles
• Aging the beef for an extended time
• Extreme cold temperatures in the freezer

Essentially, anything that exposes raw beef to oxygen can set the stage for the formation of metmyoglobin and greenish discoloration.

Is Green Beef Safe to Eat?

The green color itself does not indicate spoiled or unsafe beef. As long as your fresh beef hasn’t surpassed its use-by date and has been continuously refrigerated at 40°F or below, the green areas are likely still fine to eat.

Follow these guidelines for consuming green beef:

• Examine the texture and smell. Fresh, unspoiled beef will still have a firm, moist texture without any sliminess. It should smell slightly meaty rather than ammonia-like.

• Trim off any slimy parts. Use a clean knife to cut away any seriously discolored or slimy sections.

• Cook thoroughly to 160°F. Cooking destroys any bacteria that may be present and renders the meat safe to eat.

• Use it soon. Cooked green beef should be consumed within 3-4 days. The off-putting color often precedes spoilage.

• When in doubt, toss it out! If the beef has an odd odor, texture, or extensive discoloration, it’s better to be safe than sorry.

Why Refrigeration Causes Greening

You might be wondering why properly refrigerating beef sometimes contributes to it turning green. Shouldn’t cold temperatures keep it fresh?

While refrigeration does inhibit bacterial growth, the cold air lacks oxygen content compared to the ambient air. This means less oxymyoglobin can form, allowing more metmyoglobin to develop in refrigerated beef.

Freezing has an even more pronounced effect. The freezing process forces meat fibers to rupture, exposing more interior myoglobin to oxygen. Very cold freezer temperatures also facilitate metmyoglobin formation.

Other Factors Promoting Green Beef

Aside from the fridge or freezer itself, certain meats and preparation methods make greening more likely:

Type of Beef Cut

• Ground beef – The grinding process incorporates oxygen throughout the meat, hastening metmyoglobin development.

• Deli meats – Slicing distributes oxygen, while the extended refrigerated shelf life gives more opportunity for greening.

• Steaks – The irregular shape and thin edges of steaks mean more surface area exposed to air during aging or freezing.

Preparation and Handling

• Aging – Dry-aging beef for flavor enhancement requires prolonged refrigerated storage.

• Partial cooking – Rare or medium-rare beef retains interior myoglobin that can oxidize into metmyoglobin.

• Freezing – The freezing process itself introduces oxygen. Freeze-thaw cycles also expedite metmyoglobin formation.

• Repeated opening/closing package – This exposes the meat to more oxygen. Reseal tightly or place in a new bag.

Preventing Green Discoloration in Beef

While a little greening here and there is harmless, an unappetizing color can diminish the appeal of the meat. Follow these tips to minimize greening:

• Place beef in a sealable container or bag, pressing out excess air before sealing.

• If freezing beef, use a freezer-safe vacuum sealer to remove oxygen.

• Thaw beef in the refrigerator rather than at room temperature to reduce oxidation.

• Cook beef within 2 days of purchasing raw beef or thawing frozen beef.

• Don’t allow raw meat juices to remain on cooked beef—rinse or pat dry.

• Use frozen beef within 9-12 months for best flavor and appearance.

• Marinate beef in the refrigerator, turning the bag occasionally to redistribute pigment.

• Add antioxidants like lemon juice or vinegar to marinades to help prevent greening.

Should You Avoid Eating Green Beef?

The green color may be visually unsettling, but beef that has turned partially green is usually still safe for consumption. Unless the meat has a bad odor, odd texture, or feels slimy, green beef is fine to eat when prepared properly.

While an anaerobic environment like vacuum sealing prevents greening, some exposure to oxygen is unavoidable during refrigeration. Just be diligent in checking for any seriously discolored or spoiled spots and trim them off before cooking. Then cook the beef thoroughly until 160°F internal temperature to eliminate any risks.

If the green color is limited to small patches rather than extensive areas, the beef is still perfectly safe. You may just want to avoid serving it when looks matter. But for recipes like beef chili, stew, or skewers where the meat gets chopped or cubed, mild greening won’t affect the dish’s appeal at all.

In the rare instance that beef turns a vivid, bright green, it may be safest to discard it. But typically, those unsettling green spots are no cause for food waste or safety concerns. Handle raw beef properly, store it correctly, and cook it thoroughly, and you can enjoy green beef without worry!