Indonesia is one of the most fermentation-rich regions in the world. With thousands of islands, a hot and humid climate, and a long history of preserving food without refrigeration, fermentation became an everyday skill rather than a specialised craft.

What makes Indonesian fermentation especially fascinating is its range. Not only beans and grains, but also roots, fish, shrimp, fruit, and even durian are fermented. Often using wild cultures and simple tools, passed down through families.

Let’s explore these ferments a little more deeply: how they’re made, how they’re eaten, and what they teach us.

Why Fermentation Became Essential in Indonesia

In tropical climates, fresh food spoils quickly. Fermentation helped Indonesian communities to:

• preserve food safely,

• reduce toxins in roots and beans,

• improve digestibility,

• enhance flavour without spices or sugar,

• and stretch precious protein sources.

Much like other traditional foodways, fermentation in Indonesia relied on salt, time, warmth, and microbes, not precision equipment.

Tempe – Indonesia’s Most Famous Ferment

Tempe originates from Java and has been eaten for centuries.

How tempe is traditionally made

1. Whole soybeans are soaked overnight.
2. The skins are removed (important for digestibility).
3. Beans are lightly cooked and drained.
4. They are inoculated with a mould culture (Rhizopus).
5. The beans ferment for around 24–48 hours in a warm environment.
6. The mould binds the beans together into a firm “cake”.

Unlike miso or soy sauce, tempe is:

• not aged for months,
• not a paste,
• and not heavily salted.

How tempe is traditionally eaten

• Sliced and fried in animal fat.

• Grilled or pan-seared and served with eggs or fish.

• Added to soups or stews.

• Eaten as part of a mixed plate, never on its own.

It was historically paired with:

• small fish,

• eggs,

• broths,

• and fermented condiments.

Tape (Tapai) – Fermented Rice & Cassava

Tape is one of Indonesia’s most common household ferments.

How tape is made

Cooked rice or cassava is:

1. cooled,
2. sprinkled with ragi (a mixed starter of yeasts and bacteria),
3. wrapped or covered,
4. and fermented for 2–5 days.

Cassava fermentation is especially important because raw cassava contains natural toxins.

How tape is eaten

• As a small dessert or snack.

• Mixed into drinks.

• Used in traditional sweets.

• Sometimes cooked into cakes.

Tape is lightly alcoholic, sweet-sour, and soft in texture, a very different ferment from salty vegetable or fish ferments.

Tauco – Aged Fermented Bean Paste

Tauco is an old, slow ferment and is used much more like a condiment.

How tauco is made

1. Soybeans are cooked and inoculated with mould.
2. The beans are sun-dried and fermented.
3. They are then aged in salt brine for several months.

This long fermentation develops a deep savoury flavour.

How tauco is eaten

• Used in tiny amounts.

• Stirred into sauces.

• Added to vegetable or fish dishes.

• Used like anchovy paste or fish sauce.

It was never eaten by the spoonful; it’s a flavouring, not a main food.

Oncom – The Zero-Waste Ferment

Oncom is one of Indonesia’s most unusual ferments.

How oncom is made

1. Leftover peanut press cake or soy pulp is inoculated with mould.
2. Fermented for a short time until it binds together.
3. Often lightly cooked afterwards.

How it’s eaten

• Sliced and fried.

• Crumbled into vegetable dishes.

• Used as a protein extender rather than a main protein.

Oncom reflects a culture where nothing was wasted.

Terasi (Trassi) – Fermented Shrimp Paste

Terasi is one of the most nutritionally interesting Indonesian ferments.

How terasi is made

1. Tiny shrimp or krill are mixed with salt.
2. The mixture is sun-fermented.
3. It is dried, ground, and sometimes fermented again.
4. The paste is aged until deeply aromatic.

How terasi is eaten

• Used in very small amounts.

• Toasted briefly to mellow the aroma.

• Added to sambals, soups, and sauces.

Similar to:

• Roman garum,

• Asian fish sauces

• Middle Eastern fish sauces,

• Scandinavian fermented fish pastes.

Pekasam – Fermented Fish

Pekasam is a traditional method of preserving fish in inland areas.

How pekasam is made

1. Fish is cleaned and salted.
2. Mixed with cooked rice or another carbohydrate.
3. Packed tightly and fermented for weeks or months.

How it’s eaten

• Fried or cooked before eating.

• Served with rice and vegetables.

• Used as a savoury protein source during lean seasons.

Fermentation softens bones and enhances mineral availability.

Tempoyak – Fermented Durian

Tempoyak is strong, even by Indonesian standards.

How it’s made

1. Fresh durian pulp is salted lightly.
2. Left to ferment naturally for several days.

How it’s eaten

• Used as a condiment.

• Added to fish dishes or soups.

• Mixed into sambals.

It’s never eaten in large amounts; it’s a flavour enhancer.

Fermentation Starters – Simple & Traditional

Indonesian fermentation relies on:

• handmade starters (ragi),

• wild microbes,

• warmth and humidity,

• and experience rather than measurements.

Starters were shared, inherited, and guarded carefully, much like sourdough cultures in Europe.

What Indonesian Fermentation Teaches Us

Across all these foods, we see the same principles:

• Fermentation makes unsafe foods safe.

• Small amounts are enough.

• Ferments support flavour, digestion, and preservation.

• Protein was always paired with other nutrient-dense foods.

• Fermentation is embedded in daily life, not “health culture”.

Final Thoughts

Indonesia’s fermented foods are bold, practical, and deeply ancestral. From mould-bound tempe to fermented cassava, shrimp paste, and fish, these foods show how humans worked with microbes to survive and nourish themselves in challenging environments.

The wisdom of fermentation is wonderful to learn from and experiment with yourself. 

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Disclaimer: The content of this blog post is for informational purposes only and is not intended as medical advice. While I strive to provide accurate, well-researched, and up-to-date information, I am not a licensed medical professional. The insights shared here are based on personal research and experience. I encourage you to conduct your own research and consult a qualified healthcare provider before making any health-related decisions. Your well-being is important, and any actions taken based on the information in this blog are solely at your own discretion and risk.