Hello! What you experienced is very common, and as a chef, I get this question all the time from home cooks. That distinct sour aroma when opening vacuum-sealed meat is known as confinement odor, and in most cases, it is completely normal and does not mean your pork ribs have gone bad.
Modern vacuum packaging, often referred to as Cryovac, works by removing virtually all oxygen from inside the pouch to prevent aerobic spoilage bacteria from multiplying. However, harmless, naturally occurring lactic acid bacteria continue to thrive in oxygen-free environments. Over time in the package, these bacteria produce lactic acid and trace gases as they interact with the natural juices, known as purge, that collect around the meat. Because the package is tightly sealed, these organic acids and gases remain trapped until you cut the plastic open, releasing them all at once into a concentrated burst that smells sour or slightly sulfurous.
To determine if your ribs are perfectly fine or actually spoiled, you just need to let the meat breathe for a short while. Remove the ribs from the plastic packaging, throw away the bag and juices, and pat the surface dry with paper towels. Set the ribs on a tray or cutting board and let them rest in a well-ventilated space for 15 to 20 minutes. As the trapped gases dissipate and oxygen reaches the surface of the meat, the sour smell should fade completely, leaving behind the mild, normal scent of fresh pork.
On the other hand, if the strong sour or pungent odor persists after 20 to 30 minutes of airing out, or if it smells like ammonia or rotten eggs, the meat has likely spoiled and should be discarded. You should also check the texture and appearance. Fresh meat should be moist and firm, while spoiled meat will feel sticky or slimy to the touch, or show unusual grayish or greenish discoloration. A bloated or ballooned package prior to opening is another warning sign that bad bacteria have produced excess gas inside.
