When the Appam Turns Too Sour: How Climate Change Is Transforming the Taste of Fermented Foods

Recently, my mother noticed something unusual while preparing appam batter at home. Traditionally, she ferments the mixture using a little coconut water and sugar-no yeast, just natural fermentation as our ancestors did. But these days, the batter ferments too quickly, turning overly sour within hours, and its usable life span has drastically reduced. When she mentioned this to her friends, they too shared similar experiences, all guessing vaguely that it might be “because of the weather.”

 Appam 

Batter

Indeed, Kerala’s recent climate, rainy and overcast days, persistently high humidity, moderate temperatures, and sudden bursts of heat, creates ideal conditions for accelerated microbial activity. Such fluctuations stimulate the growth of lactic acid bacteria and wild yeasts that drive fermentation, but the delicate balance between them becomes unstable when the ambient temperature fluctuates even by 2–3°C. The result: over-acidified, sour batter with a shortened shelf life.

I recently watched a YouTube interview featuring a Ramassery idli maker from Palakkad, who lamented how the batter quality has degraded over the years. He attributed this to declining raw material quality and the overuse of chemical fertilizers and pesticides in agriculture. While his point about ingredient degradation is valid, he missed a crucial factor, the influence of changing weather patterns and microclimatic conditions on fermentation behavior itself.

Ramassery idli

This humble kitchen experience opens the door to a deeper scientific question: How is climate change altering the quality, taste, and safety of fermented foods globally?

The Science of Fermentation

Fermentation is a microbial biochemical process that transforms carbohydrates into acids, alcohol, or gases through the action of bacteria, yeasts, or molds. In foods like appam, dosa, or idli, lactic acid bacteria (LAB) such as Lactobacillus species and wild yeasts like Saccharomyces cerevisiae work in harmony to create the characteristic texture, aroma, and mild tanginess.

This delicate process depends on several environmental factors:

• Temperature, which controls enzyme kinetics and microbial growth rate.

• Humidity, which affects water activity and microbial balance.

• pH and ingredient composition, which determine which microbes dominate.

Even small shifts in temperature or moisture can disrupt this equilibrium, tipping the balance from beneficial microbes to spoilage organisms. What once yielded a mild, fluffy appam can now turn sour, sticky, or spoil within a day.

Global Impacts of Climate Change on Fermentation

Rising Temperatures and Accelerated Fermentation

Warmer ambient temperatures stimulate microbial metabolism, reducing fermentation time but often causing excessive acid production. This results in overly sour batters, stronger alcoholic notes in beverages, and shorter shelf life. In tropical regions like Kerala, this means that fermentations that once took 8–10 hours now complete in half the time, often resulting in over-fermentation and acidity. In cooler regions, the same warming can enhance fermentation efficiency but distort flavour balance.

In Japan, recent studies have confirmed that rising temperatures are affecting the fermentation of miso and soy sauce, leading to faster fermentation but noticeable changes in aroma and flavor. According to researchers from Japan’s National Agriculture and Food Research Organization (NARO), this shift is linked to enhanced enzymatic and microbial activity driven by warmer environments. Similarly, in Europe, winemakers report that higher temperatures increase grape sugar content, leading to faster yeast fermentation and higher alcohol content, altering the balance of taste and aroma that defines traditional wines.

Humidity, Rainfall, and Microbial Instability and contamination

Rising humidity levels, especially in coastal and monsoonal regions, like those seen recently in Kerala, foster rapid microbial multiplication. Such conditions also encourage the growth of undesirable bacteria and molds, raising concerns about contamination and spoilage. High moisture can encourage molds or spoilage bacteria to dominate open fermentations such as appam, dosa, kimchi, and sauerkraut. Similar problems are documented in Africa and Southeast Asia, where fermented cassava (gari) and fish products spoil faster under humid, variable conditions.

Changes in Raw Material Quality

Climate change affects crops and raw ingredients at the biochemical level. Variations in rainfall and temperature can alter the starch, sugar, and protein content of grains and pulses, directly influencing fermentation behavior.

In Kerala, rising temperatures and irregular rainfall patterns impact rice cultivation, changing the starch-to-protein ratio crucial for batter fermentation. Similarly, pesticide residues and soil degradation alter the microbial flora naturally present on grains, which are essential for spontaneous fermentation.

• In India, variations in rainfall and temperature modify the starch and sugar content of rice and pulses, the very substrates of idli and appam batter.
• In Europe, warmer grape harvests raise sugar levels, affecting wine fermentation kinetics and alcohol yield.
• In Korea, unpredictable seasons alter cabbage texture and moisture, changing kimchi’s flavor and storage stability.
• Even Mediterranean cheese and yogurt producers now struggle to maintain traditional flavor as warmer cellar temperatures disturb ageing and microbial maturation.

A similar pattern is seen in apple cultivation, where climate change alters both physical and chemical properties of the fruit, reducing firmness, acidity, and colour intensity while increasing susceptibility to pests and irregular sugar accumulation. These changes in fruit quality reflect how climate-driven biochemical shifts can ripple across the entire food chain, influencing even the raw ingredients used in fermentation.

Altered Microbial Ecology

Traditional fermented foods rely on indigenous microbial communities shaped by local climate. When temperature and humidity patterns shift, so does this microbial ecology.

For example:

• In European sourdough, warmer summers change Lactobacillus species composition.

• In Korean kimchi, milder winters cause faster acidification and sharper flavors.

• In African cereal fermentations, fluctuating temperatures reduce lactic acid bacterial diversity.

These examples show that even traditional microbial “signatures” built over centuries, are evolving under new climatic pressures.

Food Safety and Nutritional Implications

Uncontrolled or accelerated fermentation can cause the buildup of biogenic amines (histamine, tyramine) and mycotoxins, leading to food intolerance or contamination. A WHO-supported 2023 report highlighted that elevated fermentation temperatures in tropical regions increase such risks.

Fermentation usually enhances nutrition, but over-fermentation or microbial imbalance may reduce vitamin and probiotic content. Thus, climate-induced irregularities threaten not just flavor, but safety and health value.

Industrial and Sustainability Perspectives

Maintaining consistency is now a growing challenge for both traditional and industrial producers. Breweries, dairies, and batter companies use energy-intensive climate-controlled systems to stabilize fermentation, raising production costs and carbon footprints.

In South India, small-scale idli batter makers increasingly face reduced shelf life, flavor inconsistency, and customer complaints, subtle signs of a global food system under climatic stress.

Reflections from Kerala: The Local Mirror of a Global Trend

Kerala’s monsoon-driven climate has always nurtured naturally fermented foods from toddy to appam and dosa. But changing humidity and heat spikes have shortened batter life drastically; what once lasted 2–3 days now spoils within 18-24 hours.
Researchers at the Kerala Agricultural University (KAU) and Central Institute of Fisheries Technology (CIFT) have noted similar microbial instability in traditional foods due to prolonged humidity and fluctuating temperatures.

Adapting Through Knowledge and Innovation

Communities and industries are now experimenting with adaptive strategies:

• Adopt shorter fermentation times and cooler storage environments.

• Use thermostable or controlled starter cultures adapted to temperature fluctuations.

• Monitor local weather data to optimize fermentation scheduling.

• Reduce chemical contamination of ingredients to maintain microbial health.

• Improve the quality of raw materials to restore microbial balance and stability.

Such measures merge traditional wisdom with modern scientific understanding, preserving both flavor and safety.

        From the kitchens of Kerala to the fermentation vats of Japan, climate change is quietly transforming the microbial ecosystems that shape our food. What once fermented overnight now ferments in hours; what once tasted balanced now feels off.

The extra-sour appam batter in my mother’s kitchen is a humble yet powerful reminder that climate change has entered our homes, influencing the invisible microbial choreography that sustains our culinary traditions.

As we adapt our recipes, storage, and methods, we must also recognize that each food culture is a living expression of local climate and biodiversity. Protecting our planet means protecting these delicate microbial partnerships, because in every spoonful of fermented food, we taste not just science, but the living climate of our Earth.