Have you ever wondered how much caffeine is there in your cup of tea? It may be stated on the packaging but that may not necessarily correlate to the content that you consume. This is because there are some scientific theories behind this. There is an optimal brewing time for tea to obtain the maximum caffeine content. It depends on the type of tea one is consuming but some research has been done on Oolong tea to identify its optimal brewing time. These concepts are not commonly taught in school but ae very much applicable from theories discussed in school. Many students seeking Chemistry tuition can appreciate these links better as Chemistry tutors spend time to explain the practical links in the subject.
The properties of Caffeine
Caffeine, also known as trimethylxanthine has a molecular formula, C8H10N4O2, and structural formula as shown below. Caffeine dissolves in the boiling water upon the addition of the tea bag. Caffeine dissolves in water as there are partial negative oxygen and nitrogen atoms in the caffeine molecule which can form hydrogen bonds with the water molecules. These concepts of bonding are taught further in a student’s education curriculum, in particular at the Junior College level. Chemistry tuition allows students to link these concepts at an earlier level. Chemistry tutors emphasise on the concepts of bonding in Chemistry tuition given its depth and links to real-life situations, as shown with something as simple as drinking tea.
Caffeine Molecule (Images from: https://en.wikipedia.org/wiki/Caffeine)
The process of tea brewing
When you add a tea bag into a glass of hot water, the chemicals in the tea bag diffuse out into the glass of water. Other than caffeine, two other significant chemicals diffuse out of the teabag. These two compounds present together in tea allows one to control the caffeine concentration of the tea. According to some studies, when boiling water is poured onto the tea leaves, caffeine is drawn out faster than any other chemical, including tannins which gradually diffuse out of the tea leaves. After a few minutes, tannins will begin to cancel out the effects of caffeine, thereby causing the caffeine concentration to decrease as brewing time increases further.
Making the perfect cup of Tea
Now that the properties of caffeine and the contents of tea have been discussed, how is it then that the cup of tea with the maximum content of caffeine is made. Studies on oolong tea specifically have shown that a rough brewing time of ten minutes is likely to bring about the maximum caffeine concentration in tea. This is likely to be applicable across the different types of tea as they all contain similar chemicals that result in such outcomes.
Why does this occur? A common type of tannin, an astringent and polyphenolic biomolecule, is thearubigins that are found in large amounts in oolong tea. The caffeine concentration increases up until the 10-minute brewing interval as caffeine molecules diffuse out of the tea bags faster than thearubigins. This results in an overall increase in caffeine concentration despite its reaction with thearubigins. This occurs as thearubigins diffuse out at a slower rate than caffeine leading to fewer caffeine molecules reacting with thearubigins than it was diffusing out of the tea bags. Past the 10-minute brewing interval, the caffeine concentration decreases. This could be explained as the concentration gradient between the solution and the tea bag reduces, slowing the diffusion rate of caffeine. The effect of tannins on caffeine can be explained by how tannins are acidic compounds while caffeine is a basic compound, thus in the presence of water, these two can neutralize, cancelling out the effects of caffeine. While this may sound complicated, students seek Chemistry tuition as they wish to learn more and conduct research on such areas. This is summarised in the chemical equation below.
C8H10N4O2 + C43H34O22 → Salt + Water
Therefore, the effect of tannins is said to reduce the caffeine concentration of tea and it is important to find the optimal brewing time to maximize the caffeine concentration of tea. When studying such topics, Chemistry tutors help students understand real-life reactions in their Chemistry tuition lessons so that they may appreciate the subject better.
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