Kategori: Chemistry Education

It is early autumn. Your fridge and freezer are overflowing with raspberries, black berries and other berries you have collected over the summer. What to do to make room? Make jam! Besides preserving fruits and berries, it is also great fun with some interesting chemistry involved. You can see the result of my first attempt to make jam from black berries I picked during late summer in the image above.

What do you need to make jam? You will need equal amounts of fruit and sugar in weight. I will refer to a recipe used for 1 kg of fruit and 1kg of sugar. The task of the sugar is to bind water and draw it away from the fruit. With no water available, no mould will be able to grow on jam which causes the preserving effect. As you can see, it is important to use enough sugar, but too much of it will lead to the formation of sugar crystals. In addition, acidity is needed, so the jam can set properly. Fruits naturally contain some acids, but more will have to be added for certain fruits like berries to reach the perfect pH for jam to set, which is at 2.8 to 3.3. To reach this pH-value, you can either add citric acid or use jam sugar where citric acid is already contained. I chose another method and added the lemon juce pressed from one lemon which naturally contains a lot of acid.

What happens after mixing together fruit, sugar and acid? The mixture is first heated and stirred until all the sugar has dissolved and the boiling point is reached. Then continue to boil gently for 15 to 20 minutes. What happens now is that the pectin molecules, which consist of long chains of sugar molecules linked together, react with each other to form a network of long chains. This reaction happens at 104.5 degrees Celsius and it gives jam its gel-like texture. Fruits contain pectin, but in different amounts. For example black berries that I chose to make my jam do not contain enough pectin to form a gel. In this case, jam sugar can be used, which contains pectin additionally to the citric acid. It is also possible to add one fruit that is high in pectin to the jam making process, which could be an apple or a citrus fruit. Instead, I decided to add four table spoons of grated lemon zest, which also contains pectin. In fact, pectin added to jam sugars is made from the peels of citrus fruit.

The jam is ready to pour into jars, when enough pectin molecules have reacted to form the gel-network. You can test when this point is reached by taking some of the jam up with a cold spoon and letting it cool. Then observe how the jam moves when you move the spoon around. It should just stick to the spoon and stay in one place, when the pectin network has set sufficiently. Make sure, to wash your glass jars with soap and hot water before using them. You can even heat them in an oven at 160 degrees Celsius for sterilization. To create a vacuum inside the glas jars, put them into a pan with hot water before filling them. Pour the jam into the jars when it is still hot, then screw the lit on and remove them from the hot water bath. As the glass jars cool, the vacuum will slowly come on. This is yet another precaution, to make the jam last as long as possible.

Making jam proved to be great fun for the chemist, the food enthsiast and the environmental activist inside me. It is a great way to preserve locally grown berries and fruits for the winter which is  much more environmentally friendly than buying berries in winter that have come all the way Chile or New Zealand. It is also better than having jam from a supermarket of which you have no idea where it comes from and under which conditions it has been been made. In addition, I found that opening a glass of my own home-made jam is far more exciting and satisfying.

Cooking and frying cause chemical changes in food and lead to the formation of new substances. One obvious change is that many foods like meat, eggs or potatoes turn brown when being fried. This is caused by a chemical process called the Maillard reaction. This reaction takes place between an amino acid and a reducing sugar. In the reaction, the carbonyl group of the sugar reacts with the amino group of the amino acid and forms a new substance with a brown colour and a better taste. There are many different sugars and amino acids in food which is why the number of different brown, well-tasting products is very large. The Maillard reaction requires the addition of heat and does not occur before 140 degrees Celsius. This reaction is responsible for the colour and taste of a great variety of foods. Besides the well-known colour of fried (or grilled) meat, eggs, potatoes and other vegetables, it is also resposible for the brown colour and taste of toasted bread as well as roasted coffee beans.

Another process which happens during both frying and cooking is the denaturation of proteins. Large protein molecules are normally folded in a very specific way. During denaturation they unfold. This process can be compared to unfolding a piece of Origami art until only a sheet of crumpled paper is left. These crumpled proteins can easily become entangled with each other in a process called coagulation. In addition, the cell walls of vegetables like potatos and carrots are broken down by high temperatures when being cooked or fried. This makes them easier to digest for us humans as compared to eating them raw.

Like for frying, the Maillard reaction plays an important role for baking too and causes the brown colour cakes take on when they are placed in an oven. Other browning reactions like the caramalization of sugars take place as well. Caramalization is the oxidation of sugars which turns them into brown products. It should be noted that caramalization happens at different temperatures for various sugars. Fructose, for example caramalizes at only 110 degrees Celsius, while 160 degrees are necessary to caramalize glucose. The denaturation and following coagulation of proteins is essential for baking too because it results in the stiffening of the dough.

Today, the chemical reactions caused by so-called raising agents are important as well. Baking powder and self-raising flour normally contain a substance called sodium bicarbonate (also known as baking soda) and a solid acid. When water and heat are added this mixture releases the gas carbon dioxide which gives cakes their fluffy textures. Evaporating water further contributes to this process which is called expansion.

Fluffy cakes as we know them today first entered the kitchen in the 18th and 19th century. Before that, cakes were generally flat and rather heavy, like fruited tea cakes for example. During the time of the first fluffy cakes sodium bicarbonate had not been discovered yet. Instead, yeast was often used as a raising agent and it is still used today in some countries to bake bread. Another method was to beat eggs before adding them to the dough until they contained enough air bubbles, a method that could take a long time and required strong arm muscles.

The reactions taking place during deep-frying resemble in parts the ones during cooking and frying. The Maillard reaction, the denaturation and following coagulation of proteins as well as the break-down of cell walls happen here too. But due to the higher temperatures even more reactions like oxidations and polymerizations can take place, even in the frying oil itself. Another problem is that while the frying oil extracts nutriants like vitamins and minerals, it also creeps into the food and adds high numbers of calories. For this reason, deep-fried food is normally less healthy than its regularly fried or cooked counter parts. This can easily be shown by the example of a large baked potato which normally contains about 220 calories and 1 g of fat. If the same potato is cut up and turned into chips (or French fries), it will contain almost 700 calories and 34 g of fat. In conclusion, deep-frying creates very well-tasting foods, but it is important not to consume them on a regular basis.

Before the industrial revolution in the 19th century, the range of colours available for paintings was rather limited. Only naturally occuring earth pigments, minerals and some materials of biologic origin, for example insects, could be used.

While earth pigments like ochre and other iron oxides have been since the stone age, other colours were much more difficult to obtain. They had to be traded over long distances during the middle ages and the renaissance. Some colours like blue and purple were especially expensive and became associated with royalty. In the 18th century, the first cheaper, synthetic colours, for example Prussian blue and Scheele’s green, were invented which made them more accessible to artists.

These colours normally came in powder form and when an artist got a hold of the pigments he needed they still had to be mixed with a liquid. For oil paintings, the powders were normally mixed with linseed oil forming a paste which had to be used right away. Other painting techniques preferred other liquids, for example water was mixed with colour pigments to create watercolor paintings called ”aquarelle” in French. This technique is still very common in school art lessons today.

Let us go through different colours and look at how they have been produced throughout history. You can even find the information in the infographic above.

Red – This colour can be created with iron(III) oxide which has been used since the cave paintings of the stone age. During the Roman Empire and the middle ages, another red pigment called ”minium” with the chemical name lead(II,IV) oxide became popular, especially to colour manuscripts. Lead-containing substances like minium are poisonous and small amounts are accumulated in the body during permanet exposure. This shows that not all the colours used by artists throughout history were safe and we will encounter even more toxic pigments further on. Fortunately, a non-toxic red pigment came into use during the 16th century. It consisted of the dried, pulverized bodies of female cochineal bugs from Southern America. This pigment is still used today, for example in lipstick colours.

Yellow – Also yellow pigments have been around since the stone age. They were produced from ochre, which has the chemical name hydrated iron oxide. In 1797, the synthetic pigment chrome yellow, also called lead(II) chromate, was invented by mixing solutions of lead nitrate and potassium chromate. It became popular among artists during the first half of the 19th century. Due to the contained lead and chromium this pigment was poisonous as well.

Blue – Before the 18th century the main source of blue pigments was a semi-precious stone called ”lapis lazuli” which could only be found in one mountain range in Afghanistan. This is the main reason for its high price and the difficulty to obtain blue colours. The situation changed in 1704 when Prussian blue was invented as a cheaper, synthestic pigment. Prussian blue refers to range of compounds that are made up from iron, carbon and nitrogen. Carbon and nitrogen are joint together as cyanide ions that form so-called coordination complexes with iron in the center. Despite the presence of cyanide ions, these pigments are non-toxic and still in use today.

Green – Originally, the mineral malachite with the chemical name copper carbonate hydroxide has been employed as green pigments. In 1775, the Swedish chemist Carl Wilhelm Scheele invented a substance called copper arsenite which became a popular pigment under the name Scheele’s green. You might have guessed it from the chemical name, this compound contained arsenic which made it very toxic. Among all the poisonous colouring agents that have been used throughout history, this was probably the most lethal one. Especially its use in wall paper and clothing has been linked to many deaths during the 19th century in Britain and Europe.

Violet – Traditionally, mixtures of red and blue were used to create violet. The difficulty in obtaining blue colours made violet very expensive as well. During the 19th century, the first synthetic, cheaper pigment called manganese violet became available. Its chemical name is ammonium manganese(III) pyrophosphate and it is still used in cosmetics such as makeup and hair colouring.

White – For a long time, a compound called lead carbonate hydroxide or white lead was used to produce white colours for paintings. But just like lead(II,IV) oxide (minium), its use is banned today due to the toxicity caused by the contained lead. The white pigment most commonly employed now in paints is titanium(IV) oxide.

Black – Just like red and yellow, black pigments have been around since the stone age and quite easy to make. The earliest black pigment was probably charcoal produced by burning wood or other vegetation. A popular method to create black pigments during the 17th and 18th century was burning animal bones in air-free chambers which resulted in pigments referred to as ”bone black”.

Soap is made via a chemical reaction between a fat and sodium hydroxide (NaOH). The reaction is called saponification and produces salts which consist of sodium ions and fatty-acid ions. The latter have one long chain of carbon atoms each. These sodium-ion fatty-acid salts are very good at removing dirt and we also call them soaps. Their secret is that the non-polar, long carbon chains of the fatty acids are aranged in spheres around the non-polar dirt particles. The opposite chain ends, where the polar sodium ions are attached, face the polar water. These arrangements are called micelles and they can dissolve dirt from your clothes or skin.

Making soap in this way is actually quite environmentally friendly. Sodium hydroxide is normally used in the form of lye which is made by leaching wood ashes with water. Historically, the fat has often come from animals, but today fats from plants, such as olive oil or grapeseed oil, are used since they create nicer soaps. In summary, soap can today easily be produced using only renewable sources from plants.

Sounds like soap making is an eco-friendly process? Yes, but unfortunately reality looks very different. When I researched this topic, I was really shocked when I found out which substances are actually being put into these products, despite better knowledge.

Let us start by talking about the actual cleaning agents, the substances that remove the dirt. Traditionally, soaps as described above have been used for this task and I believed that this was still the case. But it turns out that today most cleaning agents are made from petroleum instead of vegetable oils. These petroleum-based chemicals work the same way as real soap does by forming micelles around dirt particles to dissolve them. They are, for example, found in laundry detergent and liquid body wash. Only bar soaps still contain the more environmentally benign, real soaps. But be careful, not all of them do. You should check if it actually says ”soap” on the packaging to be sure.

There are even more reasons why solid soap products are more environmentally friendly. On average the production of bar soap consumes five times less energy than liquid soap. Another important factor is water. Liquid soaps as well as liquid laundry detergents contain 80 % more water than their solid counterparts. In addition, liquid products come in non-reusable plastic bottles, while the solid products come in cardboard packaging.

Besides the petroleum-based cleaning agents, manufacturers often add a range of other questionable chemicals to liquid soaps. One famous example are parabens which are added to about 85 % of all liquid cosmetic products to prevent bacteria and fungus growth. Parabens can be mistaken for estrogen by the body which has been linked to both breast cancer and reproductive issues. It will be interesting to see if they could be related to the recently reported drop in sperm count among Western men. Also, paraben substitutes like phenoxy ethanol should be used with caution. Bar soaps and other solid cosmetic products, on the other hand, do not need any preservatives and are a healthier choice.

Some harmful chemicals could also be hiding under the label ”fragrance” or ”parfume”. Their compositions do not have to be revealed as they are considered trade secrets which leaves the consumer clueless about what they are made of. At least one villain chemical, called phthalates which has been linked to many health issues, is often included in parfumes as a preservative.

So, the bottom line is: use bar soaps, make sure that it contains real soap and check that all contents are revealed. As for laundry detergent, washing powder is better than liquid detergent. You can also easily make your own laundry detergent and bar soaps at home.