Sugar as a natural preservative

Using sugar to prolong the life of foods goes back to the time of Alexander the Great. His contemporaries – who didn’t know the complexity of sugar chemistry that we apply today in our lab at Ragus – were grinding fruit and adding sugar to not only preserve it, but to make a whole new product: jam.

When sugar is added to fresh foods, like fruits and vegetables, it creates an osmotic effect: sugar absorbs water in the food. Bacteria, yeast and moulds – the primary causes of most food spoilage – need water to grow and multiply. Lowering the water content in a food product means there are fewer free water molecules for these microorganisms to consume, creating an environment that makes it hard for them to survive.

In some foods, sugar produces other substances that act as preservatives, like alcohol and acids. For example, yeast converts sugar to ethanol in wine, beer and other fermented drinks. In these cases, the alcohol or acid produced are both preservatives themselves, because they have a similar inhibiting effect on microorganisms.

Another example of using sugar as a preservative involves ‘desiccating’ food by dehydration and then packing it into a jar with crystalline sugar or a high-density liquid sugar, like one of our syrups, or molasses. This helps to preserve fruits and vegetables by creating a low water activity environment that is hostile to harmful microorganisms.

Sugar has unique properties that alternatives like aspartame, sucralose and sugar ‘alcohols’ like malitol and xylitol can’t equal. Manufacturers who try to use artificial sweeteners to produce the same results as sugar are likely to be disappointed, as their chemical structures are completely different: a biscuit made with sucralose instead of sugar won’t look or taste anything like a real biscuit. We also don’t yet know what the long-term consumption of sugar substitutes has on our health, as we’ve only been using them in the food and beverage industry for a few decades.

That lovely golden-brown colour of biscuits, breads and other baked goods is down to sugar. That happens through two processes: something called the Maillard reaction, and caramelisation. The Maillard reaction takes place under heat between sugars (predominantly glucose and fructose) and amino acids (proteins).

In caramelisation, sugars (mainly sucrose, glucose and fructose) are broken down under heat, producing new molecules that provide colour and flavour, like the richness of caramel sauce or toffee. The only way to create that without sugar is with artificial flavourings and colourings.

We learnt above that sugar acts as a preservative in foods and beverages because it prevents microbial growth by reducing the water activity in a product through osmosis, or dehydration. This makes sugar a ‘humectant’: it always ‘tries’ to reach the same level of water present in the foodstuff it is in contact with. To achieve this, the water molecules in the food product are replaced by sugar molecules. Deprived of this water, bacteria find it extremely difficult to multiply. The less they multiply, the longer your food product keeps fresh.

As an added bonus, the moisture makes food better to eat too, as anyone who has eaten a dry piece of cake or bread can testify! That’s why for mouthfeel, you can’t beat invert syrups. Due to their high affinity for water, manufacturers often use them to achieve the twin goals of great texture and extended shelf life with one ingredient.

Interestingly, another way sugar inhibits microbial growth is by disrupting the enzyme activities of microbes and weakening the molecular structure of their DNA. As a result, the ability of microbes to develop and inflict damage is limited, so products remain fresher for longer. That’s why you can store foods and beverages with a high sugar concentration without refrigerating them, saving energy and production costs.

So, when manufacturers take sugar out of a product and replace it with an artificial sweetener, it’s not just the sweetness that goes: sugar’s moisture retaining powers mean that the preservative properties are lost too, along with the mouthfeel that makes a product a pleasure to eat.

As most manufacturers don’t want a shorter shelf life for their products, some opt for other kinds of preservatives, which don’t usually bring the characteristic texture and eating experience we’ve all come to expect from our favourite foods. Health-conscious consumers are increasingly avoiding these kinds of highly-processed, denatured preservatives.

Sugar is a time-tested, centuries old preserver of foods for cultures all over the world. From jams to chutneys, hams to pickles and cookies to cakes, it brings not just deliciousness, texture and flavour to both traditional, ancestral foods and modern products in today’s supermarkets and restaurants, but longevity too.

Ragus manufactures high-quality pure sugars in bulk quantities for the food and beverage industry. To learn more about our products, please contact our Customer Services Team. To see more sugar news and updates, continue browsing SUGARTALK and follow Ragus on LinkedIn.