I find that roast beef in the refrigerator starts going bad within 24 hours and after a couple of days, it is noticeably bad smelling.
How can I keep the roast beef fresh? How do butcher's do it?
I'm going to assume you are talking about deli-style sliced roast beef here. There are a couple of ways to help preserve meat freshness better.
Wrap it in butcher paper. This type of food-grade wrapping paper is inexpensive and can be purchased at many general stores and office supply stores. It works great for all sorts of meat, poultry and even fish, and can be used in the refrigerator and freezer.
Keep it in the coldest section of your refrigerator. It is often near the top or the back, varies depending on refrigerator model.
As an after thought, an assumption was made that we are talking about deli sliced roast beef. If it's not sliced, there's another option.
I usually buy a 3 or 4 pound roast and cook it at 200 degrees, 1 hour per pound. That should get you an internal temp of about 140 (rare). You want to let the roast sit for 30-60 minutes after it comes out of the oven. You don't need to have all kinds of Martha Stewart cleverness to get a great roast. Just coat with slat and pepper and pop it in the oven. I like to trim off the fat and I'll sometimes give it a good coating of teriyaki sauce. If you don't already own a good digital thermometer, get one! ...Indispensable for meat, fish and bread.
So now, to your question. If you want to extend the life, just slice off the amount that you need and put the rest back in the fridge. I happen to own a big monster deli meat slicer. Glad I bought it but it's not something many people can afford or have space for. It only takes a minute or two to slice that whole roast but slicing the whole thing up front lets in tons of oxygen. Better to keep the roast tightly wrapped and just slice off what you need.
I am a bit amazed that somebody questioned my suggestion about keeping the meat cold and keeping oxygen out. This is pretty basic food protection. I would find something else to do if invited over to their houses for dinner. The rearranging your sock drawer excuse usually works.
Besides keeping your roast beef cold and tightly wrapped, you can add a salt brine. Other than that, your best choices are to freeze it or scarf down what you have as quick as you can. If you keep it cold and the oxygen out, you can keep it a week. Rare beef will lose it's redness. The key is whether it smells OK.
If you know anything about aged beef, it's all about letting the outside of the meat "go bad" under controlled humidity and temperature. When it's time to eat the meat, the outside is trimmed away. Oxygen never gets to the inside so the inside beef remains good to eat...but it gets additional flavor from the aging.
Last resort, add the sliced roast beef to a pot and add some gravy, preferably homemade and not the store bought junk. Then make some roast beef sandwiches. You can add your favorite toppings...cheese, onions, etc.
The short answer, the best you can hope for under normal circumstances is a week so plan to eat it or toss it by then. Freeze it if you need to keep it longer.
Cold air moves down and warm air rises. So I am a bit skeptical that the coldest part of any fridge is at the top. Buy a fridge thermometer or two if you don't believe me. Do your own tests.
I know in my fridge, anything I put in the lowest drawer will start getting ice crystals.
Not sure what butcher paper is exactly but bacteria likes oxygen. For this reason, I suggest using Ziploc bags and squeezing out as much air as possible as you seal the bag. My thought is paper will not block oxygen and although it might slow things down, it's not an ideal solution.
If you cook a lot and often have sliced meats to preserve, investigate purchasing a vacuum sealer.
A salt brine might help but I couldn't tell you the proper ratio of salt to water would be. Commercial producers use nitrites and other preservatives. A brine that's powerful enough to kill the bacteria might also make your roast beef unpalatable.
And if you really want to go "out there", try an ultraviolet light wand. The UV light destroys the DNA of most micro organisms and prevents them from reproducing...effectively killing them.
Back in the 1960's and 70's there was a movement to use radiation to basically sterilize food. It never caught on due to real or imaginary effects of the radiation. That said, irradiated food would last indefinitely. I believe the NASA astronauts eat irradiated foods. There are some foods that are approved for radiation in the US...such as spices.
From a general perspective what others have said makes sense, however, warm air rises, cold air sinks, and unless you're talking about botulina, bacteria grows in the presence of oxygen, Botulina is anaerobic. So a Ziploc with the air squeezed out is better than paper. A vacuum sealer is even better.
So generally accepted as fact, one should place food at the lowest part of the fridge assuming the coldest part is desired. Refrigerator thermometers are relatively inexpensive.
Removing all oxygen will slow bacteria. That's why deli meats are generally sold in vacuum sealed pouches...and they also generally contain salt and other preservatives.
Choosing between letting people get sick...or not. It's better to speak up.
There's a complete lists of foods that may be irradiated on the FDA website. Interestingly, beef is on the list.
As far as the UV wand, that's only effective for whatever comes in contact with the UV light, provided the light is strong enough and of sufficient duration. Short answer, UV will not be effective for preserving roast beef.
When in doubt, throw it out. Your nose knows. If it smells bad, it probably is.
Still, even after all that, your roast beef will not last forever, but you can freeze it and keep it viable for several months. Foodsafety.gov recommends 2 to 6 months for freezing meat leftovers.