No matter how clever and calculating we are in the kitchen, it is very easy that at some point we prepare more food than we end up eating, especially if we have celebrated a party, a family or friends gathering and even if we have only prepared a simple dinner. Something we must be particularly attentive to. Even if it may not seem like it, food leftovers are a perfect and dynamic environment in which microorganisms, especially bacteria, can play an important but unwanted role. What leftovers can be dangerous? Why? Can we minimize the risk?
Not all food scraps are created equal.
The shelf life of leftovers depends on factors such as their preparation, proper storage, and, most importantly, the type of food. Having leftover sautéed vegetables or croquettes is not the same as eating fish or rice salad. This is because some foods are more likely to harbor pathogens such as bacteria.
Special attention should be paid to cooked rice or pasta containing bacteria. Bacillus cereusespecially when heated, because even though it starts out as an inactive spore, once heated it can become activated and release toxins. These spores are tenacious and can survive even after the grain is cooked.
The problem is that the longer we leave food at room temperature, the more bacteria multiply. We must also keep in mind that these bacteria are particularly dangerous because they are heat resistant. Therefore, even after reheating, the bacteria can still be alive and ready to spoil our food.
The general recommendation is to save leftover rice and pasta – as well as all other foods – and store them in the refrigerator or freezer as soon as possible.
We also need to be careful with meat and chicken because, largely due to their high protein content, the development of pathogens is more than likely if we do not store them quickly in the refrigerator and consume them within one to two days. If ground meat and poultry have been cooked to a safe temperature, they can be stored in the refrigerator for one to two days, as long as they are stored at a temperature of around 5 ºC or less. Other meats such as steaks or fillets will keep a little longer, between three and four days in the refrigerator.
Egg-based foods are also particularly vulnerable, such as poorly curdled sauces or tortillas, as they expose us to a greater risk of salmonellosis. In the case of sauces made without heat treatment, it is best to consume them at the same time. Otherwise, we must refrigerate them immediately and consume them as soon as possible.
Fish and seafood are also very vulnerable to contamination, so it is best to finish the dish the same day it is cooked.
What happens with fruits and vegetables? Should we also be careful with this type of leftovers? In this case, the problem lies in the fact that we leave the pieces half-cut or peeled, which increases the surface in contact with possible microorganisms. As this study points out, cut fruits and vegetables, being perishable foods and more susceptible to contamination, can facilitate the growth of pathogenic and decomposition microorganisms.
What if the leftovers are a combination of different foods, like salads? A good rule of thumb here is to base it on which ingredient in the dish goes bad first. A seafood rice dish will only last as long as the seafood does, which is a higher-risk food than rice.
How to Prepare Leftovers to Reduce Risk
One of the rules we hear all the time is that there is a danger zone, which extends from 4ºC to 60ºC, in which we should not leave food for more than two hours because that is when bacteria begin to multiply rapidly (one hour if the outside temperature exceeds 30ºC). What do we do if they are still very hot? Can we put them in the fridge?
In this case, a very useful tip that will prevent us from having leftovers on the counter for a long time is to distribute the food in different containers, preferably if they are small and shallow, so that they cool faster. The less time it takes for the food to cool, the better. With a large container, this process may take longer than necessary.
We already know that refrigeration is essential to properly preserve leftovers. The same goes for how we store them in the refrigerator. The containers for its manufacture must be airtight to avoid cross-contamination and possible loss of moisture.
It is also worth remembering that before consuming leftover food, it is essential to reheat it, as heat kills bacteria – taking into account the case of pasta and rice mentioned above. The piece of leftover fillet from the day before or the breaded chicken breast should be heated to a minimum temperature of around 75ºC, and we will heat soups, sauces or stews until boiling.
It is very likely that when we reheat food, we do it in the ubiquitous microwave. If this is the case, we must be careful to stir the food well while it is heating so that it reaches all corners. One way to achieve good heating is to use a microwave-safe container with a lid, as this will ensure that the leftovers are heated more evenly and will retain moisture better.
Last but not least, if when we reheat a dish we have not finished it, we must throw it away. It is not advisable to reheat the same leftovers over and over again. If we do not want unpleasant surprises, it is better to reheat food only once.
In general, you should never keep leftovers for more than four days – with the exception of fish, seafood or cooked rice, which will last no more than a day or two. And always, if there is any doubt about the freshness or safety of a food, it is best to throw it out: the types of bacteria that can affect us do not necessarily have to affect the taste, smell or appearance of the food.
