pH
The Power of Hydrogen, or pH, is a measure of how acidic (<7) or basic (>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
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FAQs
Frequently Asked Questions
Supplies
- Centrifuge Tubes (SKU: G1005-50-2)
- Blank Label Sheets
- Label Template (Download)
- We supply 50 mL centrifuge tubes and labels for local Santa Barbara clients upon request.
Best Practices
- Collect a sample of your wine in a way that is most representative of the entire lot (i.e. practice flushing your sample valve, collecting after movements like pumpovers, stirring your barrel, etc.).
Label
- Label each sample appropriately with your Client ID, Sample Date, and Sample ID. Samples for Phenolics analysis also require a Crush Date, Varietal, and Appellation. The analysis cannot be performed without the applicable information for each sample.
- Mark the panel.
- Individual parameters can be added at the bottom of the label. A full list can be found on our ANALYSES page.
Clients are able to submit samples by contacting us directly and scheduling a pickup, delivering directly to our lab, or sending via the mail.
To arrange for pickup, clients must be located near Lompoc, Buellton, Santa Ynez, Goleta, or Santa Barbara and notify us by 11 am for same-day retrieval. Please contact us for more information.
- We provide same-day results by 7 pm with a guaranteed turnaround within 24 hours of sample receipt.
- Samples that are not analyzed same-daly are refrigerated overnight and analyzed first thing the next morning.
- Results are delivered via email in PDF format and uploaded to your account.
- Our invoices are sent via email and are due upon receipt.
- Your payment iOur invoices are sent via email and are due upon receipt.
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To ensure their stability, we ask our clients freeze their juice samples before shipment. Please contact Bound with any additional questions about sample preparation before shipment. We recommend expedited same-day to one-day shipping with a tracking number included.
Frozen
Samples can be placed in a freezer 24-hours in advance and shipped with an ice pack. Do not over-fill the polypropylene tubes or use glass containers as the frozen liquid will expand and could pose a safety concern. Freezing samples is a better alternative to boiling when analyzing compounds like ethanol, volatile acidity, free sulfur, and phenolics. Label each sample as "FROZEN".