Ground beef goes bad much quicker than steak. Grinding meat exposes more surface area to oxygen during the grinding process. Oxygen is one of the primary sources of sustenance for the tiny bacteria that cause food poisoning. The structure of ground meat forms a multitude of little air pockets throughout the meat; each one of these pockets is a breeding ground for bacteria.
Bacteria: Contamination vs. Spoilage
Contamination and spoilage are different and will impact food (and anyone who eats that food) differently.
Contamination can lead to food poisoning and is often caused by salmonella or e. Coli. One of the characteristics of contaminated food is that it displays no signs of being harmful. The meat has no off smells, texture changes, or discoloration. A tainted burger can appear, and in fact be, perfectly "fresh."
Food spoilage is simply an umbrella term for the various signs that communicate to your senses of smell, sight, or touch, that you should not eat the food. Spoilage is also caused by bacteria, but the bacteria that cause spoilage will not make you sick. This is because most of us won't eat food that smells bad or feels slimy. Even if we did, it would mostly just taste and smell very bad. Spoilage is a function of freshness (or lack thereof), whereas contamination (food that is tainted by pathogens that make you sick) can occur even in foods that are otherwise "fresh."
Is Your Ground Beef Spoiled?
In ground beef, the signs you'll detect will depend on how badly spoiled it is.
If it feels slimy, it's starting to go bad. The slime on the surface is caused by the buildup of bacterial cells. If it smells funky or off, it's spoiled. The smell is caused by the gases produced by the bacteria. Finally, ground beef can change color when it spoils, going from the familiar rust-red color (produced by iron, the same ingredient that gives blood its color) to a flat gray color.
This color change occurs as the bacteria break down the iron compounds in the meat.
If your ground beef is gray, slimy, or smelly, it's spoiled.
Keeping Ground Beef Fresh
To avoid wasting food, take action when you purchase ground beef. Either cook it or freeze it within a day or two of buying it. Usually, you'll see a sell-by date on the package. Even if that date is two or three days in the future, pay no attention to it. Cook the meat the day you bring it home or freeze it. (Freezing does not kill the bacteria that cause spoilage or food poisoning, but it does slow down the reproductive cycle. Bacteria goes into a state of suspended animation.)
If you are using the meat for burgers, you can plan ahead and season the meat, form it into patties, transfer the patties to freezer bags, and freeze them. When you are ready to use them, thaw them overnight in the refrigerator. If you have less time to thaw, place the baggie in a casserole dish in the sink and run cold water over it. Make sure the burgers are submerged and there is a constant flow of cold running water. Note: It has to be cold water. If you use hot or even warm water, you could ruin the meat.