pH

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The Power of Hydrogen, or pH, is a measure of how acidic (7) a solution is on a logarithmic scale. It’s the most fundamental analysis in all of winemaking informing us of microbial inhibition, chemical speciation, and tartrate stability. At wine pH (~pH 3-4), there are no dangerous pathogens to human life, and this has largely shaped the traditions and legislature around winemaking. Since there is no risk of food born illness, winemakers have far more leeway with winery sanitation than with other food products. Nevertheless, pH helps winemakers understand the proclivity of wine towards spoilage, thus giving them a framework for sanitary demand. Rather than thinking of sanitation as an absolute, we can address its demand as a spectrum relevant to the style of wine one hopes to achieve. The limits for cleaning and sanitation are well-defined: Clean: removal of soil and 90% reduction of colony forming units. Disinfection: a reduction of 99.9% of colony forming units. Sanitation: a reduction of 99.999% colony forming units. Sterilization: a reduction of 99.9999% colony forming units. Chemical sterilants include 0.2% peracetic acid (PAA) and 7.5% hydrogen peroxide (H2O2) (Mohapatra, 2017). As a biological transformation, winemaking exists within a grey area of the this spectrum. It begins with understanding how low pH inhibits microbial growth by disrupting the structure and function of essential proteins within the cell. Increased hydrogen ions at low pH disrupt the weak bonds holding protein molecules together, preventing them from performing their essential functions and hindering microbial ability. Yeasts and bacteria in wine adapt to low pH conditions by regulating hydrogen ion concentrations in their cells, but their presence in wine is conditional to a variety of environmental factors including temperature and alcohol. Similarly, pH, temperature, and alcohol also effect the speciation of chemicals in wine, most notably sulfur, phenolics, and metals. Free SO2, in particular, is a measurement of SO2 that is unbound to other molecules. Its molecular form (SO2) is an antimicrobial preservative that’s speciation in wine is highly pH dependent. A “good” pH for sulfur is below 3.6 where molecular sulfur exists, but in practice this isn’t the best for structured red wines. This is because a low pH actually breaks the salivary barrier and slows the oxidation of phenolics making red wines more astringent. This is why an pH of 3.3 is appropriate for low structure varietals like Pinot Noir, but not high structure varietals like Cabernet Sauvignon. Furthermore, highly pigmented red wines have free anthocyanins that readily bind to molecular SO2, diminishing their antimicrobial effect, and demonstrating there is no perfect pH for wine. The level of cleanliness in a winery is subject to a winemaker’s microbiome of desire. For instance, premium Cabernet Sauvignon producers with high pHs tend to have immaculate cellars with strict sanitation and risk adverse protocols like inoculating with cultivated yeast, whereas small lot Pinot Noir producers tend to take more risks with spontaneous fermentations in porous vessels with less sulfur. How we determine the design and practices for each wine style will be based on sanitary demand, the primary function of pH. It is important to note, however, that there is no definitive limits for these decisions. Spontaneous fermentations can be executed at pH 4.5 as well as at pH 3.5. The most important distinction is one’s careful attention to detail. To learn more about pH and its importance in winemaking, become a Bound advising client. References Colantuoni, G., McLeod, S. WINEXRAY LLC. https://www.winexray.com/ Gawel, R. (1998). Red wine astringency: A review. Australian Journal of Grape and Wine Research, 4(2), 74–95. https://doi.org/10.1111/j.1755-0238.1998.tb00137.x Jenkins, T. W., Howe, P. A., Sacks, G. L., & Waterhouse, A. L. (2020). Determination of Molecular and “Truly” Free Sulfur Dioxide in Wine: A Comparison of Headspace and Conventional Methods. American Journal of Enology and Viticulture, 71(3), 222–230. https://doi.org/10.5344/ajev.2020.19052 Kallithraka, S., Bakker, J., & Clifford, M. N. (1997). Effect of pH on Astringency in Model Solutions and Wines. Journal of Agricultural and Food Chemistry, 45(6), 2211–2216. https://doi.org/10.1021/jf960871l Mohapatra, S. (2017). Sterilization and Disinfection. Essentials of Neuroanesthesia, 929–944. https://doi.org/10.1016/B978-0-12-805299-0.00059-2 Singleton, V. L. (1987). Oxygen with Phenols and Related Reactions in Musts, Wines, and Model Systems: Observations and Practical Implications. American Journal of Enology and Viticulture, 38(1), 69–77. https://doi.org/10.5344/ajev.1987.38.1.69 Smith, C. (2013). Postmodern Winemaking: Rethinking the Modern Science of an Ancient Craft. University of California Press. Sotres, J., Lindh, L., & Arnebrant, T. (2011). Friction Force Spectroscopy as a Tool to Study the Strength and Structure of Salivary Films. Langmuir, 27(22), 13692–13700. https://doi.org/10.1021/la202870c Show more