I just bought this meat yesterday, but when I broke the block apart to cook tacos, the inside is completely grey while the outside is red. It smells okay, but it looks unappetizing and risky

The Science: Why Ground Beef Turns Grey

The secret behind ground beef’s color comes down to a protein called myoglobin, which holds iron and stores oxygen in muscle tissue. How myoglobin reacts with the environment determines the hue of your meat:

• The Red Outside (Oxymyoglobin): When ground beef is exposed to oxygen in the air—even through oxygen-permeable plastic wrap at the grocery store—myoglobin binds with oxygen to create oxymyoglobin. This is what produces that familiar, vibrant cherry-red color.

• The Grey Inside (Deoxymyoglobin): Deep inside the tightly packed block of ground meat, oxygen cannot penetrate. Deprived of oxygen, the myoglobin shifts into a greyish, brownish, or purplish state.

Because your meat was fresh enough that oxygen only reached the surface, the interior remained oxygen-starved. Once you break the block apart and expose the grey core to the air, it will often begin to turn red within 15 to 20 minutes!

The Ultimate Freshness Checklist

Since visual cues alone can be misleading, use your other senses to determine if your ground beef is truly safe to cook:

The Golden Rule: The smell test is your most reliable gauge. Since you mentioned the meat smells completely normal and fine, the interior discoloration is almost certainly due to oxygen deprivation rather than bacterial growth.

Tips for Cooking Your Taco Night Safely

Now that you know the meat is safe, here is how to turn it into delicious taco filling:

1. Break it Down: Crumble the beef directly into a hot pan. As it cooks, heat will turn all the protein uniform brown anyway.

2. Brown First, Season Later: Let the meat brown thoroughly to build flavor via the Maillard reaction before draining excess liquid and adding your taco seasoning and water.

3. Cook to Temperature: Always cook ground beef to an internal temperature of 160°F (71°C) to ensure food safety regardless of initial appearance