A few things you need to know about water for making coffee!

The Carbonate System

The carbonate system refers to factors related to water quality: TDS, hardness (GH), acidity and alkalinity, pH, buffer index (KH), metal content, especially calcium and magnesium. When evaluating water for brewing coffee, the above factors and their interactions must be considered comprehensively.

Total dissolved solids (TDS)

Also known as the total dissolved solids, the higher the TDS value, the more dissolved matter is contained in the water, including both inorganic and organic matter. The measurement unit is: milligrams per liter (mg/L).

• Milligrams (mg)/L indicates how many milligrams of total dissolved solids are in 1 liter of water.

• PPM is the concentration unit of parts per million of a solution. It refers to the number of milliliters of solute contained in 1 million milliliters of a solution or the number of grams of solute contained in 1 million grams of a solution.

• Conversion relationship: 1mg/l=1PPM

If the TDS value of water is less than 1,000 mg/L, it is generally considered to meet the safety standard for drinking. A high TDS value will definitely affect the taste of brewed coffee because the water has no more "space" to dissolve (contain) flavor substances. Experiments have shown that the quality of coffee brewed with water with a TDS value of 120-125 mg/L is significantly better than coffee brewed with a TDS value of 300 mg/L.

On the other hand, the types of flavor-producing substances also affect the hydrodynamic dispersion of water through the coffee bed and individual coffee particles.

The higher the ppm value, the more soluble substances there are in the water, so the extraction rate will be lower when brewing coffee;

The lower the ppm value, the less soluble matter there is in the water, so the extraction rate will be higher when extracting coffee.

According to SCA research, the ppm value of water is between 125-175, which is ideal for extracting coffee. If the ppm value is lower than 75, it is easier to over-extract; if the ppm value is higher than 225, it is easier to under-extract.

Causes of TDS formation in water

Groundwater extracted from underground aquifers or obtained by infiltrating the soil contains higher minerals (high TDS value). The limestone in the aquifer easily dissolves under acidic conditions to form hard water because the main component of limestone is calcium carbonate.

On the other hand, surface water from lakes and rivers usually has a lower TDS value (it does not often come into contact with soil minerals). However, human factors can affect TDS. For example, acid rain caused by air pollution can cause a decrease in pH and an increase in mineral content in lakes. Industrial and agricultural wastewater can increase the solid content of surface water. Despite municipal water treatment systems, in rural areas, water always carries the smell of algae and fungi, the main nitrogen-containing end product of protein metabolism in mammals and some fish (uric acid), and the smell of fertilizers in the soil.

Water absorbs and dissolves pollutants in the atmosphere during evaporation and rainfall; precipitation falls to the ground and dissolves dirt on the ground; surface water continuously dissolves minerals and chemicals it comes into contact with as it seeps into the ground or flows into rivers. Water dissolves calcium (Ca) and magnesium (Mg) ions it comes into contact with during the water cycle, which also affects the TDS of water.

Measuring TDS gives us an idea of ​​the total amount of soluble solids in the water being used. Increasing the amount of ions in the water will limit the amount of soluble solids that can be extracted from the coffee. Higher TDS values ​​will result in less flavor being extracted. The primary goal of water treatment is to adjust the TDS value to an acceptable level.

Total water hardness (GH)

Water with the same ppm value may have different hardness. Water hardness refers to the concentration of calcium and magnesium ions in water. The unit of hardness is ppm. 1ppm represents 1 mg/L of calcium carbonate in water.

The hardness of water is related to the ppm value of water. Water with a high ppm value has a relatively high content of calcium and magnesium ions, while water with a low ppm value has a relatively low content of calcium and magnesium ions. However, when different waters have the same ppm value, the soluble solid matter in the water may have different compositions. In other words, the content of calcium and magnesium ions will also be relatively different, which will also affect coffee extraction. It is one-sided to only look at the TDS value.

Some compounds or ions have a greater impact on the extraction of coffee than others during brewing. In the experiment, a single inorganic compound was added to distilled water to test its effect on coffee extraction.

The TDS value of coffee extracted with distilled water containing sodium bicarbonate is 1.29%. Sodium bicarbonate decomposes into sodium carbonate, carbon dioxide and water when dissolved in water. The carbon dioxide produced helps to fluff up the coffee particles, allowing the soluble compounds in the coffee to diffuse and speed up the extraction. A high sodium ion content will produce a salty taste.

The TDS value of coffee extracted with distilled water containing calcium chloride is 1.04%. Calcium chloride ionizes in water, generating chloride ions and calcium ions that react with soluble organic matter and carbohydrates in coffee to form precipitation. Calcium ions can also combine with specific substances to produce new flavors during the coffee brewing process.

Hard Water vs Soft Water

Water is divided into soft water and hard water. Water that does not contain or contains a small amount of calcium and magnesium ions is called soft water, and water that does not contain calcium and magnesium ions is called hard water. If the hardness of water is caused by sodium bicarbonate or magnesium bicarbonate, it is temporary hard water (when boiling temporary hard water, the sodium bicarbonate decomposes and the insoluble carbonates are precipitated, and the water changes from hard water to soft water); if it is caused by sulfates or chlorides containing calcium and magnesium, it is permanent hard water and cannot be removed after boiling. The above two types of hardness are collectively called total hardness.

Total water hardness = calcium hardness + magnesium hardness = carbonate hardness + non-carbonate hardness = temporary hardness + permanent hardness

Water is roughly divided according to its total hardness value: 0-30ppm is called soft water, and above 60ppm is called hard water.

Very hard water indicates that the water also contains other metal elements such as chlorides, sulfates, carbonates, and sodium bicarbonate. Chlorine and chloramines are used in municipal water systems to remove harmful bacteria in the water. They can cause oxidation of aromatic substances and oils, thereby destroying the flavor of coffee. They should be removed when brewing coffee. Excessive iron in water will make the coffee look green, hydrogen sulfide will make the water smell like rotten eggs, and chlorine and sulfates will make the water taste salty.

pH

Also known as the hydrogen ion concentration index: It is a scale of hydrogen ion activity in a solution, which is also a measure of the acidity and alkalinity of a solution in the usual sense. Normally, the pH value is a number between 0 and 14. When pH < 7, the solution is acidic; when pH > 7, the solution is alkaline; when pH = 7, the solution is neutral. Water is neutral at 25 degrees, corresponding to a pH value of 7.0. The stronger the alkalinity (the higher the pH value), the stronger the ability to offset acid and the stronger the effect of reducing sourness. The more alkaline the water used, the more acid-base reactions will occur in the coffee, and coffee will dissolve more easily in alkaline water.

Water dissolves carbon dioxide in the atmosphere, and the pH value is low at this time. Atmospheric pollution will further reduce the pH value of water. Water penetrates through soil and mineral layers, and acidic water dissolves minerals, and the pH value of water will increase accordingly. For groundwater deep below the surface, when it reaches the underground aquifer (sand and gravel aquifer), its pH value is relatively high and contains a lot of minerals. On the contrary, microorganisms in the soil are beneficial to the production of carbon dioxide, and carbon dioxide dissolves in water to form carbonic acid, bicarbonate, and carbonate, which will then reduce the pH value of water (increase acidity).

In areas rich in minerals, the hydrological pH will be alkaline. The typical pH value in the African Three Lakes region will be 8+. In rainforest areas, because there are a large number of fallen leaves and rotten trees, a large amount of humic acid is produced. Therefore, the water quality in Southeast Asia, West Africa, South American Amazon, and other rainforest areas is acidic.

Acids and bases in carbonate systems

The pH value is a measure of the total number of hydrogen ions in a solution. If the balance of hydrogen and hydroxide ions is not right, the solution is either acidic or basic. Too much of either ion will affect the brewing of coffee.

Not all acids or bases break down quickly in solution, as they naturally do in water or coffee, because coffee contains a large number of different compounds, including those with varying amounts of ionic bonds.

People can neutralize acids or bases, for example, by adding acid to a solution with a high pH value to achieve a neutralization effect. The hydrogen atoms in the acid and the existing hydroxide ions in the solution form water molecules. (Because of the newly added negative ions in the acid, the TDS value will increase).

Total alkalinity of water

To obtain the expected pH value, it is not enough to just measure the pH of the solution. The total alkalinity and total acidity must also be considered.

Total alkali: refers to the total amount of substances in water that can neutralize strong acids, including strong bases, weak bases, and salts of strong bases and weak acids. For example: hydroxide (OH-), carbonate (CO3-2), bicarbonate (HCO3-).

Water (solution) with the same pH value may not have the same total alkali content because the pH value directly reflects the H+ or OH- content in the water, and the total alkali content includes not only OH- but also CO3-2, HCO3- and other alkaline substances.

Solutions with the same alkalinity can have different pH values: For example, the pH value of NaOH solution with an alkalinity of 0.1mmol/L is 13, and the pH value of NaHCO3 solution with an alkalinity of 0.1mmol/L is 8.3

pH and base affect the acidity of a solution in opposite ways. You can lower the pH of a solution by adding acid, but the added acid may be consumed by the total amount of base in the solution and will not have the effect of lowering the pH of the solution.

The alkali in the solution neutralizes the acid in the coffee and causes the coffee particles to swell. In experiments, coffee brewed with carbonated water tasted very bitter, had a high pH, ​​had a bland taste, and caused the extraction process to take longer.

Buffering Index (KH Alkalinity)

KH is often misled by people to be the hardness of water. In fact, this is a wrong statement. The KH value only describes the acid carbonate (HCO3-) in temporary hardness. In chemistry, the KH value is defined as the concentration index of bicarbonate (HCO3-) and is measured in KH. Hardness (GH) is used to define the content of multivalent metal ions (magnesium ions, iron ions, etc.) in water, rather than describing the anions (bicarbonate, sulfate, etc.). Therefore, there is a clear difference between KH and GH.

Effects of KH and GH values ​​on brewing coffee

Because bicarbonate is the main buffer in water, it can neutralize any increase or decrease in free CO2 in the water, and can also suppress the fluctuation of hydrogen ions to maintain a constant pH value. Therefore, kH control is considered an indispensable procedure for water quality management.

If KH is too low, it means that the natural buffer system in the water has lost its balance, the water quality will become acidic, and it will be easily affected by neutral acidic substances, causing the pH value to drop sharply.

On the contrary, if kH is too high, the water quality will tend to be alkaline and will be easily affected by neutral alkaline substances, causing the pH value to rise sharply.

kH hardness is a method of expressing the content of anions (HCO3-) in water. This method is based on 100ml of water containing 1 mg of HCO3-, which is called 1 degree (equivalent to 10ppm concentration) and marked as 1 degree kH. It is completely different from CaCo3 (calcium carbonate) hardness, which is a method of expressing the content of cations (Mg2+, Ca2+) in water.

The size of the KH value is closely related to the buffering capacity of the buffering system. Generally speaking, the larger the KH, the greater the buffering capacity of the water body, and the smaller the pH change caused by high concentrations of CO2 entering and leaving the water body. From this point of view, in theory, the larger the KH, the better, but the larger the KH, the higher the inherent pH of the water body will be.

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