I will preface this post by asking you not to be a moron. Don't eat something just because I said its probably okay. Use your best judgment and accept the consequences. I am not responsible if you get sick. I do not prepare your food or clean out your fridge. Personal responsibility, dude. Learn it. Love it. Live it.
I grew up in a frugal household. You didn't throw out an unopened container of yogurt just because the expiration date had come and gone. You did the sniff test. Same thing with milk and anything else with a sell-by date. Green spots were cut off cheese and brown spots were cut out of fruits and vegetables. Leftovers were served for lunch or reinvented into a completely new meal the next night. (Later, my expertise in this area earned me the moniker "Queen of Leftovers"). It comes as no surprise then that about twice a month I'll receive a call, text or email from someone asking, "is this still good?"
The short answer to that question is generally yes. If it's not obvious to you by either its appearance or smell that an item has gone bad then it is generally still safe to eat. But let's go beyond that a bit into the longer answers.
First off, what is the item?
If it's questionable rice, beans, bread or other starch based item I always err on the side of caution and throw it out. Once beans, rice and other grains have been cooked they are much more susceptible to growing the organisms that can cause food born illness. Plus, these items are often so cheap that I don't feel as guilty throwing them out and starting over fresh.
For meats and poultry - if the item has been held in the refrigerator and is then reheated to the minimum safe internal temperature you should be fine for up to one week. Personally if I don't eat the leftovers within 48 hours I generally throw them out because they are simply not palatable to me at that point.
The second thing I ask when I get this question is "who is eating it?"
Young children, the elderly and folks who are already sick have weaker immune systems and you should always err on the side of caution when serving food to these folks. A healthy, robust adult might get ill, but a small child or elderly person could become gravely ill and even die from food born illness.
Instead of wondering if something is still good ensure that it lasts longer by taking care of it in the first place. A few simple steps can save you a headache (or stomachache!) later:
1. When making a large batch of something that can be frozen (chili, soup, etc) get your storage containers handy before you dish out dinner. Set aside the portions you think will be leftover and put one in the fridge for tomorrow's lunch and the rest in the freezer. You can defrost as necessary. Yes, you can put hot foods into a storage container and then directly into the freezer. Just leave a little room (called headspace) at the top for expansion as the item freezes so your containers don't crack.
2. Don't make large batches. If your recipe serves 8 and you are only 1 person convert the recipe down to perhaps 2 servings so you have enough for the next day but not so much that your leftovers will go bad. To convert a recipe divide your desired amount by the recipe yield to find your conversion factor. Then, multiply ingredient quantities by your conversion factor. For example, your recipe serves 8, but you only want to serve 2. 2 divided by 8 = .25 so you multiply your ingredients by .25. (Most of us have either doubled or halved a recipe automatically at some point. This is just going a little beyond that). If you need to serve more than what the recipe states you do the same. For example if your recipe serves 4 but you need to serve 20 you would divide by 4 and get a conversion factor of 5 so you multiply your ingredient amounts by 5. Remember: What you want is always divided by what you have before multiplying the ingredients.
3. Only purchase what you need. If you know you're going out to eat on Thursday night and will be away for the weekend don't go grocery shopping on Wednesday. Yes, the cupboard may be a bit bare until Monday when you can go to the store but it's better than watching your hard earned cash go down the drain along with the rotted cucumbers. The same goes if you're cooking. Don't buy 5lbs of beef chuck to make stew for two people. Unless of course you have room in your freezer to follow step 1 above. Otherwise, only purchase what you need for the recipe. Some staples, like canned beans or pasta you can purchase more of because they don't go bad quickly but you still need to consider your storage space and eating habits. Twelve cans of tuna purchased on sale is still a waste of money and space if you don't really eat tuna all that often.
Remember - if you have to ask me, it's probably still good. But if you follow the simple steps above you'll hopefully be enjoying fresher food more often and will hopefully be calling me to come over for dinner instead.