Because tea is better influenced in hot water than in cold water

A homemade tea with the classic sachet is a good example of solutionin which the water (solvent) extracts the compounds present in the leaves (solutes). This happens thanks to a spontaneous process called spread, According to which the molecules move from areas where there are more (with high concentration, in the sachet) towards areas where there are less (with low concentration, in water) to reach a balance between the two areas. There diffusion speed It also depends on temperature: the hot noise, the more the molecules are shaking, and move from one side to the other by increasing the kinetic energy of the system. This greater agitation accelerates the extraction of substances from the sachet, making the release of flavors, aromas and color. In cold water, on the contrary, the process is much slower.

Tea is a solution

When we prepare tea at home we are, from a chemical point of view, preparing one solution. This term indicates a homogeneous mixture consisting of two components: the solventin greater quantity, and the solutein smaller quantities and which is dissolved inside the solvent.

In our cup of tea, water represents the solvent, while solutes are all the molecules present in the chopped leaves contained in the sachet: it is mainly polyphenols (in particular catechins), polysaccharides, alkaloids (such as the Theinwhich is structurally identical to caffeine) and saponins. When we immerse the sachet in the water, these compounds begin to migrate towards the surrounding liquid. The speed with which this process takes place depends on many factors: one of the most important is the temperature water.

At higher temperatures, the molecules move more

There temperaturefrom a microscopic point of view, is nothing more than the measure of the molecules movement: The more warm a substance, the particles that compose it are faster. When we speak of movement we mean the ability of the molecules to move to space, to rotate and vibrate: all these movements contribute to the so -called kinetic energywhich we can imagine as a “movement energy”. By increasing the temperature of a substance, the kinetic energy of its molecules also increases.

At high temperatures, water molecules move with greater intensity: this phenomenon, known in chemistry as thermal agitationleads to an increase in the kinetic energy of the system. The water molecules that move more quickly they manage to more easily drag the solute molecules present in the sachet, By dispersing them in the liquid faster and increasing the spread speed with which the molecules pass from the sachet to the cup of water. The result? The color, flavor and aroma of tea spread a lot faster than what happens in cold water, Where molecular movement is reduced and the extraction of solutes is slower.

What is the diffusion?

The passage of molecules from the sachet of water tea is a spontaneous process called “spread“: the compounds naturally move from a high concentration area (the leaves in the sachet) towards a low concentration area (the water in the cup), until it reaches a situation of balance.

Like any physical phenomenon, the diffusion can also be described by a mathematical law: in this case we are talking about the First Fick lawenunciated by the German physicist Adolf Fick in 1855. The mathematical equation is as follows:

J = d δc / δx

• J represents the flow of molecules that spread (therefore what comes out of the sachet) and represents the diffusion speed
• δC represents the concentration difference Between the initial point and the final point, in our case the interior of the sachet and the water of the cup
• δx indicates the direction towards which molecules move, always according to our example, from the water to the water.
• D is called diffusion coefficient, a parameter that depends on some variable quantities that characterize the system, including the temperature.

This formula explains that the speed with which the molecules pass from the water to the water is directly proportional to the difference in concentration and the diffusion coefficient, therefore also to the temperature.