The scientific explanation of how temperature affects extraction, those who understand it are all top students

To understand the effect of temperature on coffee extraction, we need to learn some relevant knowledge step by step.

Water Solubility

The solubility of a substance can be understood as whether it can dissolve in water and how quickly it dissolves in water. Stainless steel is not easily soluble in water, but it can be dissolved in water at the right time and under the right circumstances. Some substances are completely insoluble in water.

When we talk about coffee, solubility refers to the ability of the substances contained in coffee to dissolve in water. These substances include soluble solids, liquids, and gases in coffee. Water is a good solvent (solvent). Water is a polar molecule with a high dielectric constant. It can dissolve other polar molecules very well. For example, salt (Na+, C1- ion combination) can be easily dissolved in water, but it is difficult to dissolve in non-polar solvents such as gasoline or alcohol.

To accurately understand the solubility of a substance, we need to consider three factors: solution temperature, solvent, and solute. If the substances that make up the solution have different states, the liquid substance is usually called the solvent, and the gaseous or solid substance is called the solute. If both are liquid, the one with a higher content is called the solvent, and the one with a lower content is called the solute.

Different substances dissolve at different temperatures at different rates depending on their properties. Some solutes will not dissolve unless they reach the highest temperature, while others dissolve quickly at low temperatures. The dissolution rate indicates how fast the dissolving process begins when the substance comes into contact with the solution. Factors such as the grind size of the coffee (fine grind), stirring, heating, etc. can speed up the dissolution process.

The art of brewing coffee lies in how to control this dissolution process. The quality of water is an important factor in the whole control process.

Polarity of water

A water molecule is composed of two hydrogen atoms and one oxygen atom. The oxygen atoms form a stable molecule by forming a pair of shared electron pairs with each of the two hydrogen atoms. However, since the shared electron pairs are obviously closer to the hydrogen atom, a negative charge center is formed near the oxygen atom and a positive charge center is formed near the hydrogen atom. This phenomenon is called the polarity of the water molecule . The polarity of the molecule affects the solubility of the solute. Polar substances dissolve easily in polar solvents, and vice versa.

Polarity of water

The special properties of water

Water has special properties. Its boiling point (100° from liquid to gas) and its melting point (0° from solid to liquid) are both relatively high. The density of water increases as it is heated, and its volume decreases as it melts. These properties are caused by the attraction between water molecules, a process called hydrogen bonding .

As mentioned before, a water molecule is made up of two hydrogen atoms and one oxygen atom. This is a bond at the atomic level.

Water molecules can also bond at the molecular level. The hydrogen atoms in one water molecule can attract the oxygen atoms in another nearby water molecule due to their positive and negative charges, thus forming a mutual connection force between nearby water molecules. In chemistry, this force is called a hydrogen bond.

According to the periodic table of elements, the melting point and boiling point of homologues of the same group of elements increase with the increase of molecular weight. Because of the existence of hydrogen bonds, the interaction force between water molecules is greatly enhanced. It can be imagined that if there are no hydrogen bonds in water molecules, then the melting point of water will be lower than -85° and the boiling point will be lower than -60 degrees.

The structure of water

We seldom think that water also has a structure. Water in nature does not exist in the form of a single water molecule (H2O), but is composed of several water molecules aggregated together through hydrogen bonds to form water molecule clusters, commonly known as "water molecule clusters", also known as water clusters, water clusters. Water molecule clusters are a type of water molecule cluster compound formed by a discontinuous hydrogen bond structure.

Macromolecules

4-Molecular clusters

The easiest way to get small molecular clusters of water is to heat it. The faster the molecular movement, the less conducive it is to the formation of hydrogen bonds, so heating can break up the supramolecules. At 100°C, liquid water and gaseous water are in equilibrium, and the water molecule clusters are close to single molecules, usually no more than 4 molecules.

When water is heated, the structure of water molecules decreases and the number increases, which is conducive to hydrating other chemicals. This is why temperature is important for coffee brewing and extraction.

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