Freshness and color of beef

When you buy thinly sliced ​​meat, there are times when the visible part is bright red, but the overlapping part is dark red.
It is a mistake to look at this color and think that freshness is poor.

This dark red color is actually the original color of the meat before it was cut into pieces. After the meat is cut into pieces and allowed to sit for just a few minutes, the oxygen in the air will change the color from dark red to bright red, giving us the impression of freshness.
Furthermore, after several days of continuous exposure to oxygen, the freshness of the meat declines and it turns reddish brown.

In other words, the dark red part can be said to be "freshness before being exposed to oxygen", and red is not necessarily the only freshness.
In addition, the more surface area you have, the more surface area you have, such as thinly sliced ​​meat or minced meat, so it is easier to damage because it is easier to come into contact with oxygen.
Also, supermarkets and butchers use reddish lights to make the meat look appetizing. This is why when you take your meat home and look at it, it looks worse than it did when you bought it.
From here on it's subjective.

When judging whether meat that has been stored in the refrigerator for several days can be eaten, judge by the smell, not the color of the meat.

The discoloration of meat on contact with oxygen (red oxymyoglobin → brownish metmyoglobin) is a chemical phenomenon that occurs long before the meat becomes "rotten" and degrades to a harmful state. In addition, the human sense of smell is more sophisticated than you might imagine.
*Let's eat within the basic expiration date and heat it well.