Fermentation is a natural process where microorganisms like bacteria, yeasts, and molds convert carbohydrates into simpler substances like organic acids, gases, or alcohol. This process not only acts as a natural preservative, but it also creates the unique, often tangy or sour flavors associated with these foods. The pH level of a food, which measures its acidity or alkalinity on a scale of 0 to 14, is a critical factor in determining the outcome and safety of fermentation. A pH below 7 is acidic, and above 7 is alkaline.
The Role of Lactic Acid Fermentation
The vast majority of Western fermented foods, including yogurt, sauerkraut, and kombucha, are the product of lactic acid fermentation. In this process, beneficial lactic acid bacteria convert sugars and starches into lactic acid, which significantly lowers the food's pH. This acidic environment is not only what gives these foods their characteristic tangy flavor, but it also creates a hostile environment for harmful pathogens, ensuring the food's safety and longevity. For example, the pH of fermented vegetables like sauerkraut and pickles typically drops to 4 or below.
Types of acidic fermented foods
- Yogurt and Kefir: Created by culturing milk with lactic acid bacteria. The bacteria convert lactose into lactic acid, resulting in a low pH.
- Sauerkraut and Kimchi: Shredded cabbage and other vegetables are fermented by naturally occurring lactic acid bacteria in a process known as lacto-fermentation. The acid produced preserves the vegetables.
- Kombucha: A fermented tea made with a SCOBY (Symbiotic Culture of Bacteria and Yeast). The yeast and bacteria work together to produce acids and other compounds that give kombucha its tangy flavor and low pH.
- Sourdough Bread: The starter culture, a symbiotic mix of wild yeast and lactobacilli, ferments flour and water to produce lactic acid and other acids.
The Less Common but Important Alkaline Fermentation
While acidic ferments are more common in Western diets, a diverse range of alkaline fermented foods exists, particularly in parts of Africa and Asia. These foods often use protein-rich legumes and seeds as their substrate, and the fermentation process is driven by different types of microorganisms, primarily Bacillus species. Instead of producing acids, these bacteria break down proteins into amino acids and ammonia, causing the pH to rise and creating an alkaline environment. This process is crucial for improving the digestibility and nutritional profile of the food by breaking down complex proteins and reducing anti-nutrients.
Examples of alkaline fermented foods
- Natto: A popular Japanese food made from fermented soybeans. The Bacillus subtilis bacteria ferment the soybeans, producing a pungent, sticky, and alkaline product.
- Dawadawa (Iru): A traditional West African condiment made from fermented locust beans. The fermentation process increases the pH, improves flavor, and reduces anti-nutritional compounds.
- Kinema: An alkaline-fermented soybean condiment popular in Nepal and India, prized for its flavor and improved nutrient content.
- Doenjang: A fermented soybean paste from Korea that is also alkaline in nature.
Do Acidic Ferments Create an Alkaline Effect on the Body?
This is a major point of confusion for many people. It's essential to distinguish between a food's initial pH and its effect on the body's overall pH after digestion. The 'alkaline diet' theory suggests that eating certain foods can affect the body's systemic pH, but the scientific evidence for this is limited and often misunderstood. While foods like lemons are acidic but are believed to have an alkaline-forming effect on the body, this applies to only some ferments.
For example, while sauerkraut is acidic, some claim it has an alkaline-forming effect after digestion. However, the human body has powerful and tightly regulated mechanisms to maintain blood pH within a very narrow, slightly alkaline range (7.35-7.45), regardless of the food consumed. The pH of foods has a negligible and temporary impact on systemic pH, so consuming fermented foods won't significantly change the body's internal acid-alkaline balance. The health benefits of fermented foods come from their probiotic content, improved nutrient bioavailability, and postbiotics, not from their ability to alter body pH.
Comparing Acidic and Alkaline Ferments
| Characteristic | Acidic Fermented Foods (e.g., Sauerkraut, Yogurt) | Alkaline Fermented Foods (e.g., Natto, Dawadawa) |
|---|---|---|
| Primary Microbes | Lactic acid bacteria (Lactobacillus, Leuconostoc) | Bacillus species |
| Substrate | Sugars and starches from vegetables, dairy, grains | Proteins from legumes, seeds, and beans |
| Chemical Byproducts | Lactic acid, acetic acid | Amino acids, ammonia |
| Final pH | Typically acidic (pH < 4.5) | Alkaline (pH > 7) |
| Flavor Profile | Tangy, sour | Often pungent or strong |
| Geographic Origin | Widespread (especially Western cuisine) | Primarily traditional African and Asian cuisines |
Conclusion: It Depends on the Ferment
The question of whether fermented foods are acidic or alkaline has no single answer. The pH of a fermented food is determined by the specific microorganisms involved and the ingredients being fermented. Many familiar ferments like yogurt and sauerkraut are distinctly acidic, a property vital for their preservation and tangy taste. In contrast, certain traditional foods from other cultures are intentionally fermented to be alkaline, leveraging different microbial processes to enhance their nutritional value. In both cases, the true health benefits of fermented foods stem from the probiotics, improved digestibility, and rich nutrient profiles they provide, rather than from a change to the body’s internal pH balance. Understanding these distinctions helps appreciate the diverse world of fermentation and its role in human health and culture.
How the Fermentation Process Determines pH
The environment created during fermentation is a delicate balance of chemical and microbial activity. For lactic acid fermentation, the bacteria thrive in a moderately warm, anaerobic (oxygen-free) setting. As they consume the natural sugars in the food, they produce lactic acid, which rapidly lowers the pH. This drop in pH acts as a natural barrier against spoilage-causing bacteria and other undesirable microorganisms, which typically cannot survive in an acidic environment. Conversely, alkaline fermentation, often using Bacillus strains, involves the breakdown of proteins, which releases ammonia, a basic compound. This raises the pH, creating an alkaline condition that also favors the growth of specific beneficial microbes while inhibiting others. For home fermenters, monitoring pH is a critical safety step to ensure the process has successfully created a stable, pathogen-resistant environment.
