Sugar helps reduce water availability in food, making the environment less conducive to the growth of bacteria and molds, thereby extending their shelf life.
Sugar acts as a kind of water sponge when used to preserve food. Essentially, it "captures" the available water by binding it to itself, thereby reducing the free water accessible to microorganisms. These small organisms, like bacteria or molds, need free water to multiply and thrive. The less water available, the less they can survive and reproduce. Thus, sugar lowers what is called water activity, which significantly slows down the degradation of food. This is exactly why a fruit submerged in syrup or jam lasts much longer than the same fruit left out in the open air.
Sugar primarily acts by "capturing" the water present in foods. The less available water there is, the more difficult it is for microorganisms like bacteria or molds to proliferate. Without enough moisture, their metabolism slows down significantly, preventing them from reproducing effectively. Basically, the microbes lack water, become inactive, and the food remains healthy for a longer time. This is the principle that makes jams and candied fruits so durable.
Sugar acts in a simple yet effective way: it attracts the water contained in food. Essentially, where there is a lot of sugar, water tends to naturally move towards it to balance concentrations—this is called osmosis. As a result, the cells lose their internal water, and deprived of water, the environment becomes completely uninhabitable for small organisms like bacteria and molds. Thanks to this phenomenon, very sugary foods remain much more protected from the microbes that would normally need water to proliferate comfortably.
Sucrose, primarily derived from beets or sugar cane, is probably the one you know best; it is often used in jams and syrups due to its ability to absorb water. Next, we find glucose, widely used in pastries and industrial preparations because it effectively limits the presence of free water, thus preventing mold or bacteria from proliferating too quickly. Fructose, naturally found in honey or fruits, is also useful as it provides sweetness and stability, while playing a protective role due to its antioxidant properties. Finally, some products also use glucose-fructose syrup, a very common combination in processed foods, as it is cost-effective, easy to handle, and has a great ability to retain moisture, significantly increasing the shelf life of foods.
Sugar plays a key role in allowing jams and jellies to last a long time. By capturing the available water, it prevents microorganisms (such as molds or bacteria) from developing quietly. Thanks to sugar, these little treats remain both appetizing and safe to eat for a longer time. Additionally, it gives jams their characteristic texture: that delightfully thick consistency comes partly from the sugar, which helps pectin (natural or added) to gel the fruits. Similarly, it’s no coincidence that classic recipes often recommend at least 50 to 60% sugar: this proportion ensures that the preparation will set, but also that it will store well without particular concern for several months.
Sugar is commonly used in fish or meat marinades, not only for its flavor but also for its antibacterial action, which helps naturally prolong the preservation of these foods.
The dehydration caused by sugar on microorganisms is similar to the effect of salt; this explains why jams and jellies remain stable for several months or even years when stored airtight.
A high sugar content in a food contributes to lowering the water activity (referred to as aw): below a certain value (generally below 0.85), microorganisms are virtually unable to multiply, thus allowing for extended preservation without the need for any other artificial preservatives.
The honey found intact in the Egyptian pyramids dates back several thousand years, and the secret of its perfect preservation largely lies in its high sugar content, which greatly limits the growth of bacteria and mold.
Sure! Here’s the translation: "Yes, there are substitutes such as salt, vinegar, or even chemical preservatives. However, their effectiveness and impact on the taste and texture of the final product will be very different from those achieved with sugar."
Not necessarily. The precise amount needed depends on the type of food, the kind of microorganism targeted, and the desired storage duration. However, generally speaking, the more sugar the food contains, the better its preservation will be due to a more significant reduction in water availability.
Sugar is particularly effective on fruits and foods that naturally contain water (such as in jams or jellies). It is not suitable for preserving dry products or those that are already very low in moisture, nor for products that are sensitive to a strong sweet flavor, such as meats or fish.
Signs such as mold, fermentation bubbles, unusual color changes, texture, or odor indicate that the food may be improperly stored or contaminated. In this case, avoid consuming it.
No, certain sugars like sucrose or fructose have similar preservative effects by reducing water activity, but their effectiveness varies depending on their distinct chemical properties and their concentration in food.
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