The Chemistry in Your Kitchen: Part Two

In this second installment of our series on food chemistry and microbiology, we tackle the science behind caramel, fermented food, and even the reactions that take place when we cook with oil. We'll also show you an easy food hack that can be done with the help of a special ingredient. 


[Photo credit: American Heritage Cooking website]

Do not mistake this for the Maillard browning we often aim for when cooking meats - caramelization occurs with pure sugars, like table sugar (sucrose), or simpler sugars like glucose, fructose, or galactose. This process occurs whenever you make syrup for leche flan, or caramelized onions for soups or burger toppings. Caramelization is an easy way to add pigmentation and a greater dimension of flavor to a dish.

[Photo credit: Signe Birck, Gourmet website]

When making the caramel syrup in leche flan, you usually heat sucrose in a pan without any water. Sucrose is a disaccharide, which means it is composed of two simpler sugars: glucose (the basic sugar that cells use for energy) and fructose (fruit sugar, also found in high fructose corn syrup).

[Photo credit: Jeanne Tiong,]

At the 160˚C mark, the sucrose melts and forms anhydro sugars: glucose and fructose anhydride or levulosan, collectively. The longer you heat the caramel, the darker and more bitter it becomes. Heat it some more, and you eventually end up with a much darker, insoluble substance called caramelin.

The flavor that we associate with caramels is due to the products of these reactions. Also take note that one actually doesn't need very high temperatures to caramelize. However, the reaction will definitely proceed faster. It is also possible to make solid caramel, by heating the sugar crystals at a lower temperature and over a much longer time. 


Food is fermented by the action of microbial metabolism, and can result in a wide range of products: from yogurt, to wine, to sourdough bread and even sausages. In a nutshell, it involves the conversion of carbohydrates into an acid or alcohol. The products of these reactions are what give fermented foods their characteristic flavors and tartness.

[Photo credit: Tatsuhiko Miyagawa, Flicker website]

The first kind of fermentation is something more of us are familiar with, and it's the process that takes place whenever we make bread and alcoholic drinks. In this process, sugar is ultimately converted into carbon dioxide and ethanol.

The organism used in ethanol fermentation is yeast. When making beer, the carbohydrate used is starch, and yeast lack the enzymes to convert the starch to simpler sugars. This explains why beer breweries add malt. Malt provides enzymes, hops add aroma and bitterness, and the mixture is boiled then fermented. Wines are produced from fruits, which already contain a lot of sugars. This is why you don't need to add a source of enzyme to break down the starch.

[Photo credit: Abril Uno website]

When making bread, we rely on a mixture of lactic acid bacteria (LAB) and yeasts. Sourdough bread gets its acidity from the bacteria, while the leavening is caused by the carbon dioxide gas produced by the yeast. We don't get tipsy from eating bread however, because any ethanol produced evaporates once it's in the oven.

[Photo credit: Devonwood Church website]

The second kind produces lactic acid, and is used in making yogurt and kimchi. You also start off with sugar but end up instead with lactic acid, which makes yogurt taste slightly sour. To attain this kind of fermentation, you usually add lactic acid bacteria. Lactobacillus is well-known for being added as a starter for yogurt, but it's also added to other fermented food.

[Photo credit: Mountain Feed and Farm Supply website]

Now, you might be wondering why foods left to ferment (when prepared properly) do not spoil and make us sick. This is because the microorganisms that cause spoilage and the microorganisms that cause fermentation are different. Because these microbes are different, their growth conditions are also different. To promote the growth of the desired bacteria, you have to control these conditions.

For example, when making bourbon, the wort is kept sour by adding bacteria like Lactobacillus delbrueckii. The pH level then becomes too low or acidic for spoilage microbes to grow. When making pickles, you soak cucumbers in brine and gradually increase the strength of the brine until it's a 15.9% salt solution - this is too salty for many bacteria, but can be tolerated by the desirable microbes.

However, it's still possible for the foods to spoil. For example, beer can spoil through the action of bacteria. Growth of Acetobacter spp. results in the production of acetic acid in the beer, making it sour. Imagine mixing vinegar with your beer!


Undoubtedly one of the most common cooking methods, frying food allows you to reach higher temperatures than methods that use just water. The high temperature causes the water on the surface of the food to vaporize, dehydrating it. At the same time, this helps to prevent oil from coming in, resulting in a crispy exterior and a juicy center. This might explain the appeal of eating fried chicken: the difference of textures plus the characteristic flavor caused by cooking food in oil.

[Photo credit: Shauna James Ahern, Food Network website]

The outcome of frying food depends on quite a few factors, such as the amount and temperature of the oil. For example, a little bit of oil is ideal for sauteing, and a lot of oil is used for deep-frying. Meats that are dipped in batter or breadcrumbs are also given a crispy coating with oil that is sufficiently hot, while a colder oil will give you a soggy result because more oil enters your food.

[Photo credit: Pass the Sushi website]

When frying, you also release a lot of different classes of compounds. When cooking anything with triglycerides (animal fat, for example), these are hydrolyzed to release fatty acids into the oil. You produce compounds like polymeric acids that increase the viscosity of the oil over time. You also release a lot of volatile compounds that are released into the air. These reactions directly influence physical and chemical changes in the oil, and explain why oil becomes thicker, darker, and tends to foam when you reuse it often.

Food Hack: 
How to Make Incredibly Creamy Coconut Milk
Ice Cream with Liquid Nitrogen/Dry Ice

[Photo credit: Junkee website]

Have you ever wanted to make vegan ice cream but often found your end product too grainy for your liking? After having tried grainy coconut milk ice cream from an establishment, the author decided to make her own version.

When we eat ice cream, an important characteristic that we look for is its distinct creaminess - a property that is influenced by its fat content. Soy milk, almond milk, and rice milk are often consumed as dairy substitutes by vegans and therefore can be used to make ice cream. However, their lower fat content compared to dairy (specifically, whole milk) can lead to a coarser texture.

This method will use a 1:1 mix of coconut milk and coconut cream (kakang gata), both of which have a higher fat content. Pour this mixture into a bowl, and add in 1/2 teaspoon of your flavoring. You can use vanilla or pandan extract, as an example. 

Next, add in 1/3 cup of maple syrup or honey, and mix well. The last, and most important step, is to add in liquid nitrogen or dry ice. When using dry ice, it is important that you first turn this into a powder or very small bits. Add in your liquid nitrogen or dry ice gradually as you stir vigorously, and you will notice that the mixture will start to bubble and thicken. If you add this ingredient in too quickly, then your ice cream will turn rock solid.

[Photo credit: Alice Phung, Spoonwiz website]

Once the ice cream is sufficiently thick, it can now be eaten. (If you used dry ice, make sure that all of the dry ice nuggets have sublimated before you place any in your mouth!). Dry ice also gives the bonus effect of carbonation, for those who are fond of fizzy drinks.

But how exactly does the liquid nitrogen or dry ice make your end product creamy? The secret lies with the speed at which the mixture was frozen. By freezing the ice cream mixture very quickly with the brutally cold liquid nitrogen (-196˚C) and mixing it vigorously, you help to prevent the formation of a network of large ice crystals. This method is much more effective than placing it in your home refrigerator, as it doesn't reach the right temperatures as quickly as you want it to.

Take note that some recipes for ice cream may call for egg yolks. If using this ingredient, make sure that your ice cream mixture is first heated well to cook the eggs before freezing, as you don't want to risk food poisoning.

As you can see, a greater understanding of food science is useful because it can help us to innovate, invent, and improve our culinary techniques. Have fun experimenting in the kitchen!


1. deMan, J. (1999). Principles of food chemistry. 3rd ed. USA: Aspen Publishers, Inc.
2. Fennema, O. (1996). Food chemistry. 3rd ed. CRC Press.
3. Jay, J., Loesnner, M., & Golden, D. (2005). Modern food microbiology. 7th ed. USA: Springer Science + Business     Media, Inc. 

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