The pH of grape juice and wine plays a critical role in winemaking. pH influences microbiological stability, affects the equilibrium of tartrate salts, determines the effectiveness of sulfur dioxide and enzyme additions, influences the solubility of proteins and effectiveness of bentonite, and affects red wine color as well as oxidative and browning reactions.
Since pH is a measurement, the key to understanding its role in winemaking is grasping its scientific definition: pH is a measurement of acidity and is calculated as the negative logarithm of the concentration of hydrogen ions in a solution. In other words, it is a reflection of the concentration of free moving hydrogen ions “swimming” in a solution. Pure water with a pH of 7 is considered neutral. Any solution with a pH below 7 has more free-moving hydrogen ions and tends to taste acidic or sour.
Wine is an acidic solution with a pH commonly ranging from 2.8 to 4.2. The range might seem narrow, but recall that pH is on a logarithmic scale. A wine with a pH of 3 possesses 10 times the concentration of hydrogen ions than that in a wine with a pH of 4. Thus, grape juice or wine with one decimal difference of pH can represent entirely different chemical environments. Just as animals, plants, microbes, and a lot of organic and inorganic matters behave differently in different environments, different pH levels impact winemaking.
If we look at sulfuric acid, its corrosive nature comes from the ability to give off, or dissociate, a much higher proportion of hydrogen ions in a solution, causing very low pH even if the concentration of sulfuric acid is low. This indicates that a high concentration of free hydrogen ions or low pH tends to create an inhospitable environment. Hence, low pH can naturally inhibit unwanted microbial activities, resulting in microbiological stability. For example, many lactic bacteria species are not able to conduct successful
Sorry about the late reply. I didn't receive notifications... pH is closely related to wine colour. However, when the lab performs analysis on wine colour, we can get direct results (the wavelength) from the spectrophotometer or other machines. Therefore, the method of analysis is direct. The relationship between pH and colour is something we should think of based on the results of those analyses.
Great article Gus, thank you. Is the wine colour:pH level relationship direct enough to be used for wine analysis or are there exceptions I must be aware of?
I enjoyed reading this and learning more about the cause and effect of the science of wine.. thank you!
Really good piece, this Gus. So glad I read it.
As a Chinese, so glad to see MW Zhu here, cheers!