Warming up leftovers appears to be the least dangerous part of cooking: the food is already cooked, the dish is dirty, and the food is saved. The catch with leftovers, is that they are not fixed. They transform as they are sitting and the risk is not necessarily the microwave but time, temperature and what the food was doing on the counter before it was even chilled.
According to microbiologist Anne Moscona, MD, microorganisms, mostly bacteria, are a factor in a dynamic environment that is Leftovers. Bacteria do best at the danger zone of 40 deg F to 140 deg F and certain toxins may still be present even after food is heated once more.
This list is devoted to the most usual foods that families should reheat frequently, not to mention why it is necessary to consider them again food-safety-wise.
1. Rice that was allowed to cool down/sat
An example is the ability of cooked rice to harbor Bacillus cereus spores which resist cooking. A prolonged warm period allowed to remain can allow those spores to germinate and reproduce and the toxins they cause cannot be destroyed consistently by reheating. This is the reason why rice may appear and smell healthy but cause nausea and vomiting within a short time.
Temperature and time are of greater importance than the reheat approach. Quick cooling and immediate refrigeration works against chance, as well as rice is among the leftovers that are better eaten earlier than later.
2. Spinach and broccoli as prepared meals
Lefthand greens, including spinach, are naturally endowed with nitrates. Nitrates may be converted to nitrites and nitrosamines may be produced in the case of cooked leftovers. The lessons to be determined in practice are not that cooked spinach becomes poisonous, but that repeated heating and protracted holds may incline chemical changes in an unprofitable direction.
Storage increases the risk: the more the cooked greens are left in a warm state and then chilled, the greater the opportunity of conversion. Take heavy spinach dishes off the refrigerator (quiche, creamed spinach, stewed greens), and refrigerate them immediately.
3. Re-heated chicken; more than once
When the handing of chicken leftovers is casual, e.g. by sitting them out during the clean up process, and by placing them warm in a deep container then heating them again, then cooling them again and then it happens again, leftover chicken becomes risky. Those changes in temperature provide opportunities of proliferation of pathogens like salmonella or campylobacter in case the food was contaminated or re-contaminated following cooking.
Warming up is useful when it is complete, and advice about leftover foods usually involves warming to 165degF or higher. Nevertheless, it may lead to the violation of safety in case the chicken has been at room temperature too long before, since not all risks of food poisoning can be identified by smell or taste.
4. Mushrooms (it is the storage that is the problem, not the toxins)
Mushrooms are frequently labeled as never reheat but more powerful evidence points in different directions. Where this idea originated that mushrooms reheated in a microwave oven would make them poisonous; I have no idea, but I can tell you that this is a myth, and I will in no quarter yield it up.
It is merely basic left-over hygiene: mushrooms are very perishable and are capable of absorbing microbes in handling and the kitchen setting. When a mushroom dish was left to cool down or sat, then it is not a magic reset to reheat it. The practical measures are proper refrigeration, shallow containers and eating within a reasonable time.
5. Potatoes baked warm, particularly in foil
Potatoes that are cooked are usually safe, although they can be a source of concern when they are kept warm and long and especially when they are covered with foil. Foil may reduce oxygen to the extent that botulism-related bacteria may become an issue when other conditions such as improper cooling and storage are involved.
A second reason why potato handling feels like a deception is that it is not consistently as reliable as it seems that botulinum toxin, once formed, will be neutralized through reheating. The risk-reducing kitchen move is easy, which is to unwrap, cool, and refrigerate as soon as possible instead of letting the foil-wrapped potatoes linger on the counter.
6. green or well sprouted potatoes in the leftovers
Not all potato hazards are related to warming food up and all are to do with what was in the pan to begin with. A natural toxin that is potentially found in green potatoes is referred to as solanine and sprouting may indicate increased glycoalkaloid content. At high dose levels, these compounds are known to induce gastrointestinal and neurologic effects and children are more prone to their effects due to relative smallness of the body. Here colors and bitterness come in handy. Potatoes which are markedly green, bitter or highly sprouted are better thrown away than cut and reused, particularly when preparing the meal to serve the families.
Left overs need not be feared, they simply need to be controlled. The rate at which the dish is cooled, the storage temperature and the number of times a dish was cool-hot cycled does more to create risk than does any difference between a microwave and a stovetop. In case of doubt, the most reliable kitchen weapon is garbage: the smell test does not guarantee that all the dangers are identified, and not all food is more efficiently prepared as eat fresh or cool fast, heat once, and eat it out.
