C 1: Why foods are stored in the refrigerator - biology, chemistry and safety rules

The refrigerator has become an integral part of the modern kitchen, but few people think about what why low temperatures is considered optimal for storing food. At first glance it may seem like it's just a tradition or a convenience, but behind it lies decades of scientific research in the fields of microbiology, biochemistry and food safety. Even in ancient times, people used glaciers and cellars to prolong food freshness, but only with the invention of artificial refrigeration in the 19th century, the process became controlled and accessible.

Today, the refrigerator performs several critical functions at once: it does not just “freeze” food, but creates an environment in which biochemical reactions slow downThe activity of microorganisms is suppressed and nutrients are preserved. For example, at room temperature milk sours in 6–12 hours, and in the refrigerator at +4°C it remains fresh for up to 5–7 days. But why exactly +4°C, and not 0°C or +10°C? And why do some foods, on the contrary, spoil faster in the cold? The answers lie in the physiology of bacteria, enzymatic processes and even in the structure of the cells of the products themselves.

In this article we will analyze why the refrigerator has become a standard solution for storing food, and also reveal little-known nuances - from how temperature affects vitamins, to why some fruits cannot be placed in the refrigerator next to vegetables. You will learn which processes are stopped by cold and which, on the contrary, are accelerated, and how to properly organize the space inside the chamber so that food stays fresh longer. 7 key reasonswhy the refrigerator has become a standard solution for storing food, and we will also reveal little-known nuances - from how temperature affects vitamins to why some fruits cannot be placed in the refrigerator next to vegetables. You will learn which processes are stopped by cold and which, on the contrary, are accelerated, and how to properly organize the space inside the chamber so that food stays fresh longer.

1. Bacteria and germs: how the cold “puts them to sleep”

The main reason for storing food in the refrigerator is suppression of the growth of pathogenic microorganisms. Most bacteria that cause food spoilage (for example, Salmonella, E. coli, Listeria) are mesophilic - their optimal reproduction temperature is +20...+45°C. When cooled to +4°C, their activity decreases 10–100 times, and some species go into a state of suspended animation.

However, it is important to understand: cold does not kill bacteria, but only slows down their division to a critical level. For example, in raw meat at +20°C the quantity Salmonella can double every 20 minutes, and at +4°C - only once every 6-12 hours. This is why even chilled products have a limited shelf life: microbes do not disappear, they simply “sleep”, and when returned to a warm environment, their activity will be restored.

• 🦠 Zone dangers: +5...+60°C - the ideal range for the proliferation of most foodborne pathogens.
• ❄️ Safe zone: below +4°C - bacterial growth slows down, but does not stop completely.
• ⚠️ Exception: some psychrophilic bacteria (for example, Yersinia enterocolitica) actively reproduce even at 0°C.

Interesting fact: in refrigerators with a system No Frost the temperature is distributed more evenly, which reduces the risk of the formation of “warm zones” where microbes could multiply faster. However, even in such models it is necessary to follow the rule: do not load the chamber by more than 70%to ensure normal circulation of cold air.

2. Enzymes and oxidation: why food spoils even without bacteria

Even if the products were sterile, they would still spoil due to internal biochemical processes. Fruits, meats and dairy products contain enzymes (for example, milk or apples) that cause oxidation, browning and changes in taste. Cold slows down the activity of these enzymes, but does not stop it completely. lipase in milk or polyphenol oxidase in apples), which cause oxidation, browning and changes in taste. Cold slows down the activity of these enzymes, but does not stop it completely.

A striking example is darkening of cut apples. At room temperature, the enzyme polyphenol oxidase reacts with oxygen to form brown pigments (melanins). In the refrigerator, this process is 3–5 times slower. Similarly, milk souring is associated with the work of the lactase enzyme, which breaks down lactose into lactic acid. At +4°C, this process takes days, not hours.

Important: some products, for example tomatoes or cucumbers, when stored in the refrigerator, lose their taste due to disruption of the enzymes responsible for the synthesis of aromatic compounds. It is better to keep them at +10...+12°C (for example, in special “freshness zones” of some refrigerator models).

3. Vitamins and nutrients: what is lost in the cold?

One ​​of the common myths is that the refrigerator “kills all vitamins.” In fact, it all depends on a specific vitamin and product. For example:

• 🥦 Vitamin C (in broccoli, pepper) is destroyed by 10–15% during 7 days of storage at +4°C, but at +20°C losses reach 50%.
• 🥕 Beta-carotene (in carrots) is stable in the cold, but oxidizes in the light - so it is better to store carrots in a closed container.
• 🥛 Vitamin B12 (in meat, eggs) is practically not lost when cooled, but is destroyed when frozen.
• 🍎 Polyphenols (in apples, berries) are preserved better at +1...+4°C than at room temperature.

Critical point: defrosting and re-freezing destroys up to 60% of water-soluble vitamins (C, B1, B6) due to the destruction of cell membranes. Therefore, it is better to immediately divide foods that you plan to store for a long time into portions and freeze them in a vacuum.

Research shows that the optimal temperature for preserving vitamins in most products is +1...+4°C. However, there are exceptions:

⚠️ Attention: Vitamin K (in green leafy vegetables) loses up to 30% of its activity when stored in light in the refrigerator for a long time. Store spinach, lettuce and parsley in opaque containers.

4. Humidity and structure of products: why vegetables become limp

The refrigerator not only cools, but also regulates humidity the second most important factor in maintaining freshness. Most foods contain 70-90% water, and evaporation causes wilting, loss of weight and texture. For example, unpackaged cucumbers lose up to 5% of moisture per day at +4°C, and in an airtight container - less than 1%.

The problem is that humidity varies in different areas of the refrigerator:

• 🌬️ Top shelves (closer to the freezer): drier air (humidity 50–60%) is suitable for cheeses, sausages.
• 💧 Bottom shelves and drawers: high humidity (80–90%) - ideal for vegetables and herbs.
• 🚫 Door: the most unstable zone (temperature fluctuates when opening) - it is best to store only sauces and drinks here.

For moisture-sensitive products (for example, salad, mushrooms, berries), it is recommended to use containers with controlled ventilation or paper towels that absorb excess condensation. But bread or cookies you shouldn’t store them in the refrigerator - they go stale 2-3 times faster due to moisture redistribution.

Wash the greens, dry and wrap in a paper towel

Store meat and fish in vacuum bags or on the bottom shelf (so that the juice does not drip)

Wrap cheeses in parchment, not in film (microventilation is needed)

Keep fruits with a high ethylene content (apples, bananas) separate from other products -->

5. Ethylene and the “gas war” in the refrigerator

Few people know, but many fruits and vegetables emit ethylene a gaseous hormone that accelerates ripening and aging. In the confined space of the refrigerator, ethylene accumulates and can spoil neighboring foods. For example, one apple in a closed container within 24 hours increases the concentration of ethylene to a level at which lettuce begins to turn yellow and carrots become bitter.

The most active "producers" of ethylene:

• 🍎 Apples
• 🍌 Bananas
• 🍑 Peaches and apricots
• 🥑 Avocado
• 🍅 Tomatoes (if unripe)

And the most sensitive to ethylene products:

• 🥦 Broccoli and cauliflower (turn yellow)
• 🥕 Carrots (become bitter)
• 🍓 Strawberries and raspberries (soften)
• 🥬 Leaf salads (wither)

Solution: store “ethylene” and sensitive products in separate drawers or use containers with ethylene absorbents (for example, activated carbon). Some modern refrigerators (for example Samsung Family Hub or LG InstaViewhave separate controlled atmosphere zones where ethylene levels are kept to a minimum.

What happens if you ignore ethylene?

If you leave bananas next to broccoli for 3 days, the ethylene concentration in a closed box may exceed 10 ppm (parts per million). At this level, broccoli will turn yellow, lose up to 40% of vitamin C and acquire a bitter taste. Likewise, one apple in a container with carrots will speed up their wilting by 2 times.

6. Refrigerator temperature zones: where is which?

Not all foods need to be stored at the same temperature. In a standard refrigerator, there are 4 temperature zones, each of which is suitable for certain categories of food:

Important: in refrigerators with Multi Air Flow system (for example, Bosch VitaFresh or Liebherr BioFresh) the temperature is distributed more evenly, but even in them microclimatic differences between zones remain. Always check the temperature in different parts of the chamber using a thermometer - deviations of more than 2°C from the norm can reduce the shelf life of products by 30%.

⚠️ Attention: If your refrigerator is equipped with the function Super Cool or Fast Freeze, do not forget to turn off it after use. Constant operation in intensive cooling mode leads to over-drying of food and increased energy consumption (up to +20%).

7. When the refrigerator does harm: foods that cannot be refrigerated

Despite all the benefits, some foods spoil faster in the refrigeratorlose their taste or texture. Here are the key exceptions:

• 🍍 Tropical fruits (bananas, pineapples, mangoes) - at +4°C their cell membranes are destroyed, the flesh darkens.
• 🍅 Tomatoes - cold stops the synthesis of substances, responsible for the taste, they become mealy.
• 🥑 Avocado - unripe ones will not ripen in the refrigerator, and ripe ones will turn black in 1-2 days.
• 🧀 Hard cheeses (parmesan, pecorino) - when low humidity, they become dry and crumble.
• 🍯 Honey, jam, honey —crystallize and thicken, losing consistency.
• ☕ Coffee (beans or ground) —absorbs foreign substances odors and loses aroma.
• 🍞 Bread - goes stale 2-3 times faster than at room temperature.

The optimal temperature for these products is +10...+20°C and special conditions:

• Bananas, pineapples, mangoes - store at +12...+14°C in a ventilated place.
• Tomatoes - at +15...+18°C (for example, in a kitchen cabinet).
• Avocado - at +18...+20°C until ripened, then can be transferred to the refrigerator for 1-2 days.
• Coffee and cheeses - in airtight containers at +10...+15°C (for example, in a cellar or pantry).

Exception: if there is one in your refrigerator temperature-controlled freshness zone (for example +8...+10°C), some of these products (for example, tomatoes or cheeses) can be stored there for a short time (2-3 days).

FAQ: Frequently asked questions about storing food in the refrigerator

Can thawed foods be stored in the refrigerator?

Thawed foods (meat, fish, semi-finished products) can be stored in the refrigerator no more than 24 hours at a temperature of +1...+4°C. Repeated freezing is strictly not recommended: when thawing, bacteria are activated in the product, and repeated freezing does not destroy them, it only stops growth. An exception is products defrosted in the refrigerator (not at room temperature) and not subjected to heat treatment.

Why does ice form on the back wall in the refrigerator?

Ice on the back wall is a sign malfunctions of the defrosting system (in models with a drip system) or excessive humidity. Normally, condensation should flow into the drainage hole and evaporate. If ice accumulates, check:

• Is the door closed tightly (the seal may be worn out).
• Are the shelves overloaded (air circulation is impaired).
• Is the fan working? (in models No Frost).

Regular ice formation increases energy consumption by 15–20% and can lead to compressor failure.

How often should you defrost the refrigerator?

The frequency of defrosting depends on the type of system:

• Drip system: once every 3–6 months (or when ice forms more than 5 mm thick).
• No Frost: once every 12 months (to clean the ventilation grilles).
• Low Frost: once every 6-8 months.

Before defrosting, unplug the refrigerator, take out all the products and wait for the ice to completely thaw (at least 6-8 hours). You cannot speed up the process with a hairdryer or hot water - this can damage the seals and plastic parts.

Is it possible to put hot dishes in the refrigerator?

Put hot dishes in the refrigerator not recommended in threes reasons:

1. Sharp temperature changes increase the load on the compressor, shortening its service life.
2. Steam from hot food condenses on the walls, increasing humidity and the risk of mold formation.
3. The temperature in the chamber temporarily rises, which accelerates the deterioration of other products.

Optimal: cool the dish to room temperature (but no longer than 2 hours), then transfer it to an airtight container and put it in the refrigerator.

Why do foods in the refrigerator spoil faster than indicated on the package?

The shelf life on the package is indicated for ideal conditions: temperature +4°C, humidity 80%, no cross-contamination. In reality, the rate of spoilage is affected by:

• Frequency of door opening (each time the temperature rises by 2-3°C).
• Overloading of the chamber (air circulation is disrupted).
• Proximity to “active” products (for example, raw meat next to ready-made food).
• Faulty seal or thermostat.

To prolong freshness, use vacuum bags, separate products by zone and regularly check the temperature with a thermometer.