How fast do bacteria grow on food left out?

In this article, we answer the following question: How fast do bacteria grow on food left out? We discuss the “danger zone” and how long can food be kept at room temperature before it becomes dangerous. 

How fast do bacteria grow on food left out?

How fast bacteria will grow on food left out will depend on the room temperature, but the general answer would be within two hours. The US Food and Drug Administration (FDA) advises refrigerating food as soon as possible because at room temperature (between 5ºC and 65ºC, considered the “danger zone”), the risk of bacteria growth increases with every minute.

This is the most common scenario in worldwide kitchens: we take the steak out of the freezer and leave it for hours on the kitchen counter until it is ready to cook. We do it without being aware that this practice – defrosting food at room temperature – so widespread in US homes can carry its risks.

This is a common mistake. Food does not need to defrost or be kept at room temperature. If you want to defrost something, your best option is the microwave. If you don’t like it, use cold water, without taking the food out of the container and without stagnant water.

The reason that it is so important to avoid room temperature when defrosting any food is that bacteria like the warmth and if we let them roam freely they will reproduce more easily.

Microorganisms grow at temperatures between 4 and 65ºC, which in the world of food safety translates as the ‘danger zone’.

The most important thing when defrosting is that the food is in this area for as little time as possible. And achieving this is not easy if we resort to the traditional method and to defrost we use room temperature, a slow process in which microorganisms can also run free through the water given off by the food.

How fast does bacteria grow on food? 

According to the USDA guidelines, once the food is in the temperature ranges of 40 and 140 F, the bacteria doubles every 20 minutes. The rule of thumb is that one should never leave food for more than 2 hours in hot weather conditions.

How long can food be kept at room temperature?

Perishable food: no more than two hours

Meat, fish, eggs, and leftovers should not be more than two hours at 4.44 degrees Celsius, according to the United States government. The best thing is to keep them in the fridge and keep the door closed as much as possible. In the event of a power outage at home, the food in the fridge is safe as long as no more than 4 hours pass without electricity. Federal authorities recommend that we never test the food to “determine its safety.

If after starting to consume the leftovers there are still remains, they must not remain at room temperature. The FDA recommends that it is better to freeze them before storing them in the refrigerator for several days.

Cheeses: depends on the type

Following the guidelines of the US Administration, some cheeses can be kept without refrigeration and without a time limit and others must be in the refrigerator. However, it is advisable to take out those that are refrigerated a while before to serve them at room temperature and enhance their flavor.

Cheeses such as Parmesan or provolone are safe at room temperature, but grated cheese, fresh cheese, or others considered soft, such as Roquefort, mozzarella, or cottage cheese, cannot be more than two hours at more than 4.44 degrees Celsius. The same rule applies to other dairy products, like cream.

Butter: a while to soften if we want to cook

As for butter, it has been proven that the varieties with salt do not proliferate many bacteria, so this is better than its variety without salt if we want to leave it out of the fridge to soften and use it in dishes. Be careful: if we leave it for a day or two, we will soon notice how rancid. However, even if we can keep it for a while or a few hours in a place where it is not in the sun, the best way to keep it cold.

Eggs and tortillas: no more than two hours

Classic is to prepare the mayonnaise without eggs if it is going to be consumed outdoors, especially in summer. If it is purchased and we have already opened it, the Americans recommend that it not be out of the refrigerator for more than eight hours above 50 degrees Fahrenheit, that is, 10 degrees Celsius. By the way, some industrial sauces, like ketchup or mustard, can be out of the fridge before opening.

Scrambled or hard-boiled eggs should be thrown away after sitting at room temperature for two hours or more, as bacteria growth will then proliferate. And if they are refrigerated in the supermarket where we buy them, we have to maintain the cold chain to prevent them from spoiling. 

Dishes prepared with eggs (desserts, quiche …) should also be thrown away if they spend more than two hours in the open. Tortillas, for example, should be put in the refrigerator once they cool down if they are not going to be consumed at the moment.

Homemade cakes: two days

If you’ve baked a homemade cake with fresh fruit (for example, apples), let it cool first. Then, if you want, you can put it in the fridge, but it can also be kept for one or two days in the pantry or in a dry corner and at a normal temperature. If it smells funny, throw it out.

Bread: about five days

Bread can be kept out of the fridge for several days. In fact, if we put it in the fridge it softens or molds. Of course, it will harden over time, and in cases such as sliced bread, it is advisable to keep it in its container, well-closed, or in another container. A classic to soften it in the toaster, although it must be consumed very quickly, otherwise, it will harden again.

Food chilled and frozen from the supermarket: one hour

It can also happen that you do not finish cooking the food but have bought it from the supermarket to consume at home. The key is here in the cold chain. 

According to the FDA, if more than an hour has passed between you taking them off the shelves, paying, and arriving at your home, the cold chain has been broken and it is not worth storing them again. In these cases, they should be consumed immediately. To do this, the best thing is that, when buying them, you take them when you are about to pay and put them all in the same part of the cart.

Final thoughts

In this article, we answered the following question: How fast do bacteria grow on food left out? We discussed the “danger zone” and how long can food be kept at room temperature before it becomes dangerous. 

We remind you that leaving food to cool outside the fridge may increase the risks of contaminating it with harmful bacteria. On the other hand, putting it in the fridge will make it cool unevenly and will cause condensation inside the fridge. 

What is your choice? If you have any questions or comments on the content, please let us know!

References – Are You Storing Food Safely? –  Food Safety – Be Food Safe: Protect Yourself from Food Poisoning