Water is the best and safest solvent in the world. We have discussed the solubility properties and chemistry of water in detail in our articles about water. In this article, we will look at the effect of ions on the solubility chemistry of water from a broad perspective. When ions dissolve in water, the electrolytic properties of the solution increase and the electrical conductivity of water increases. This electrical conductivity gives new properties to water. Ions interact with water molecules to form a hydrate layer, and thanks to this layer, more ions are dissolved in water. Therefore, the solvent property of water increases thanks to the increase in the electrical conductivity of water, and water becomes able to dissolve more substances. In the studies conducted by Lockhart and Pangborn on coffee and water, while trying to reach the concept of “ideal” in coffee extraction, they have drawn a path for themselves and us without ignoring unwanted metals and compounds in coffee such as transition metals, halogens, nitrate, sulfate, and phosphate. However, at the moment, we are not at the point where quality coffee production has reached, but rather we are aiming to control the amount of ions of the most useful salts such as halogens, calcium and magnesium. This is why we announced it in our previous article when we introduced FINAL TOUCH. The whole trick to brewing coffee is that your solvent collects the flavorful ones and leaves the rest in the filter. The role of dissolved ions in the dissolution of coffee components is difficult to quantify experimentally, because there are many competitive interactions, such as the dragging of water from coordination spheres to form ion pairs, and these are important both entropically and thermodynamically. The type of interaction between the dissolved ions and water varies depending on the type of interaction. For example, the hydration of Ca2+ is more exothermic than Mg2+. The dissolution of larger molecules is more complex, because the solute usually has a complex set of polar motifs. In flavor chemistry, organic compounds exhibit complex properties, with competing hydrophilic and hydrophobic regions interacting with water through hydrogen bonding, Coulombic interactions, and the formation of ordered hydrate cages. In any case, if the solute is below the saturation point of water, the electrostatics or hydrogen bonding in the larger system is not significantly altered. In line with the studies by Lockhart, the upper limit of dissolved ions in coffee extraction is not limited by saturation but by overextraction. In this context, we will focus on the role of dissolved cations in the extraction of coffee components by using literature. We will try to summarize the subject through a study. The study proposes an accessible quantum chemical approach to measure the binding of coffee organics with the familiar dissolved metal ions, Na+, Mg2+ and Ca2+. We have selected five derivative acids (1-5), caffeine (6) and eugenol (7) as representatives of the class of organic derivatives found in roasted beans at various concentrations, whose chemical structures are shown in the figures below. Of the five acids, lactic acid (1) and apple acid (2) represent sour notes, while citric acid (3) has a more popular sweet flavor. Quinic acid (4) and its larger derivative chlorogenic acid (5) are considered bitter and unpleasant. Caffeine (6) is included as an example of an aromatic alkaloid, while eugenol (7) has a pleasant woody note found in coffee, wine, and whiskey.
Dissolved cations (Cation is a positive ion that carries an electric charge. They become positively charged because they lose one or more electrons in atoms or molecules, the salts in the above and FINAL TOUCH product are in the form of cations in aqueous solution) interact with the nucleophilic motifs of the dissolved coffee components. As a short parenthesis to the positive charge I mentioned, namely the cation; the positive charge is very important, because most aroma compounds in coffee are negatively charged when dissolved in water, which means they are attracted to positively charged metal ions. This interaction can be understood with classical electrostatics: here the interaction energy Ur is the charge of the ion and the solution (qi and qs) divided by the square of the interatomic distance. Therefore, more localized charged species are expected to interact more strongly with molecular multipolar components. In other words, electrostatic interactions are determined by the charge of the ion and the solvent and the distance between them.
The 3D images of the organic substances we mentioned above are on the left. More localized charged ions are expected to interact more strongly with molecular multipolar components because the charges are more widely distributed in these components. In the figure on the side, we can see that the 1-2-3-4 compounds have a more localized (let's shorten it as non-diffuse) morphological structure.
A summary of the binding energies (relative binding energy; is the binding energy of one component with respect to another component) is shown in the adjacent figure and the H2O-M+ interaction is included in the table for reference. The separation of metal-coordinated water is an entropy driven process, but there is competitive displacement of metal-coordinated water molecules from compounds. Coordination and interaction require a higher activation energy than H2O-Mn+. the table shows which cation is a more effective playmate for the extraction of all five acids.
Similar binding tendencies are observed for Ca+2, but in all cases the relative binding energy is lower compared to Mg+2. The binding energy of 6(caffeine)-Ca+2 is comparable to that of H2O-Ca+2, which is the only example of a weakly interacting divalent cation with an electron-dense motif. Since the electron density of caffeine is spread throughout its conjugated aromatic motif, low binding energies (nearly no interaction for Na+) are obtained for all metal ions. Considering the results obtained according to the table, the binding energies are clearly proportional to the charge and inversely proportional to the ionic radius. Therefore, there is no need to explore the binding of K+, since the activation energy is expected to be lower than that of Na+ (due to the diameter). To summarize the above table briefly and more simply, the coffee bean provides a computer modeling experience in which the binding energy between seven different flavor components and magnesium, calcium or sodium ions is calculated. The results showed that all of these ions would bind and increase the extraction of seven different aroma components. It was presented that magnesium had the greatest effect in increasing the solubility effect, calcium slightly less and sodium-potassium less. Although the effect of each ion was different, it was determined that the balance of effects was approximately the same as a result of the panels. Mg+2 ion is the ion that has the strongest interactions with coffee components and allows the most components to be dissolved from coffee beans. In addition, Ca+2 ion gives quite a good result but has a lower interaction power compared to Mg+2. Na+ and K+ ions surprise us by interacting weakly with neutral components. We mentioned here that if the ratio of calcium and magnesium is not well adjusted, it hardens the water and does not increase the dissolution but decreases it.
Baking soda is not a cation or a metal. It acts as CO3-, a negatively charged cluster of carbon and oxygen atoms. The terms 'alkalinity' or 'buffer' in the case of water for coffee are all descriptions referring to baking soda.
The important feature of baking soda for us is its ability to absorb acid, namely hydronium or hydrogen ions. Baking soda can bind acid by turning it into HCO3 or H2CO3 and release it again when the acid concentration drops. For this reason, baking soda is called a 'buffer' because it provides buffering against changing acid levels. Since the sodium and potassium sources in our FINAL TOUCH product are provided in the form of bicarbonate, it also provides the buffering function mentioned in the previous sentence while supplying sodium and potassium ions to the water.
The study showed that the ideal dissolution rate of coffee beans depends on both the ionic composition and the amount of bicarbonate in the water.
Above you can see a reaction between coffee beans and magnesium ion. It is one of the most beautiful and demonstrable examples of magnesium in water binding to coffee's flavor compounds and releasing them into the brewed coffee. The structure called caryophliene (the reaction product, the heterocyclic structure on the far right of the arrow) emerges, which will allow you to taste the rose flavor of the brewed coffee.
In the sensory experience panel section of the study we reference in this article, the judges were presented with a filter brew made using "soft, no extra ion added" water and with "good" and "slightly sour acidity". Then, a filter brew was made using water with a high calcium content with the same Total Dissolved Solids (TDS) value. For this brew, Maxwell claims that the high buffering capacity eliminates other flavors. Finally, a brew is included where "all the aforementioned ions and those used in our FINAL TOUCH product work together". The panel commented and observed that the best cup was the one made with water that was ionized at an optimum level without any salt precipitation. It suggests that the magnesium ions in the water help to extract sharp, fruity flavors, the calcium emphasizes the heavier, creamier notes, and the 'buffer' substances are antagonistic to the sharper, acidic notes.
The results of the study summarized that it depends on the ionic composition of the water and the amount of bicarbonate that determines the ideal dissolution rate of coffee beans.
Coffee, which we can only shed light on a very small part of scientifically, will constantly push us to discover how much more is possible, not the concepts of “ideal/correct”, and our adventure seems to continue uninterrupted.
DUYGU KURTULUŞ
Co-Founder / Chemist / Nanotechnology Engineer / Hazardous Chemical Consultant / Chemical Evaluation Specialist