By Joanne Yeo - Wednesday, Oct 17, 2012
What if there are indeed, certain types of foods that can last forever (i.e., foods that will never or hardly spoil)? Before you get all excited about it and start making bulk purchases, and save on grocery shopping time and hassle, let’s hear what the experts in the field have to say…
Assistant Professor Liu Shaoqun from the Food Science and Technology (FST) program at the National University of Singapore (NUS) explains that how some food can be regarded as ‘immortal’ or not depends on how one defines food spoilage as.
He says food can be spoiled via the following reasons: (1) Microbial activity (e.g. growth of bacteria and molds); (2) Chemical reaction (e.g., oxidation as a result of exposure to the air); (3) Biological/ biochemical activity of the food itself. These activities can result in changes in the food and affects taste, quality, smell and colour.
To combat food spoilage due to microbial growth, proper food storage is key. In general, Assistant Professor Yuk Hyun-Gyun (from the same FST department) says the ideal storage environment for most foods is one that is low in moisture (apart from perishable foods such as vegetables and meats that require moisture to ensure good quality), minimal exposure to surrounding air, away from sunlight and finally, low temperature, which is the key factor to keep foods longer.
Prof Yuk says there are 4 keys reasons for spoilage – firstly, moisture, where molds and bacteria thrive, then there is the temperature of food storage where the “danger zone” sits between 4-60 degrees Celsius. He adds also that exposure to sunlight and even oxygen can spoil that plate of cha kway teow. The key culprits that cause damage are the biological and chemical reactions plus the effect of exposure to the elements.
Even if the foods are stored properly, it will also undergo biological changes and will naturally degrade. Prof Liu gives the example of yoghurt – it contains live cultures that will produce acids, which will turn it sour. However, he adds that even though it is considered ‘spoiled’ in terms of taste, it can still be consumed without causing harm to the body.
Depending on your definition of food spoilage, the following list of foods (and condiments) may be considered immortal, and yet not.
Soy sauce & Salt Soy sauce contains salt, which is a natural food preservative. It slows down food spoilage by preventing microbial growth. Prof Yuk explains that salt binds to water molecules and ‘removes’ the available (free, unbound water molecules) water required for microbial growth. Prof Liu explains that most microorganisms are not able to tolerate and survive in the high salt environment as they tend to lose water and get dehydrated.
Salt can last forever as it does not degrade or become stale when in its dry crystalline form, as stated on the official website of a salt producer in the United States. However, the ‘useable life can be limited by caking or lumping of salt crystals due to moisture.’
Sugar As with salt, sugar has a similar effect in inhibiting microbial growth through dehydration. When kept well and in a moisture free environment, sugar can last forever. That is, in our lifetime.
Honey It is commonly known that honey does not expire. As with sugar and salt, the high sugar content in honey results in a low water activity. Such an environment is not suitable for microbial growth, explains Prof Yuk. However, he says if it is left exposed to the air, mold will be able to grow on the surface.
Rice Uncooked rice is dry with low moisture. Prof Yuk explains that such a condition does not allow for bacterial growth.
If such dry conditions are maintained, we can keep them for as long as we want.
Hard liquor Hard liquor such as rum Chinese bai jiu (white spirit), vodka, rum and whiskey are high in alcohol (ethanol) content can last for a very long time if properly kept without exposure to the air. Prof Yuk explains that if wine is exposed to air, it will be oxidized by the oxygen in the air to produce vinegar (acetic acid) which will then lead to a change in flavour.
He adds that alcohol is anti-microbial. Thus, their growth is prevented in such drinks.
Vinegar Acetic acid is the main constituent of vinegar. Research studies conducted by the Vinegar institute, an association of vinegar manufacturers confirms that vinegar’s shelf life is almost indefinite. They explain that its acidic nature makes it self-preserving, without the need for refrigeration. White distilled vinegar, for instance, will remain virtually unchanged over a long period of time. Prof Yuk explains that the acidic environment (low pH) prevents most microbial growth. While there may be some observable changes in colour or sediment appearance, the vinegar is still edible.
Baking soda The alkaline nature of baking soda (or sodium bicarbonate) inhibits microbial growth. If kept away from moisture, the dry powder form can remain unchanged. Prof Liu adds that nothing will be able to grow on it, not even mold.