Mushroom Garum GuideA Vegetarian Fish Sauce Alternative

The science: koji, enzymes and umami

Garum is a name historically associated with a savoury sauce made by breaking down ingredients over time. In modern kitchens, the term is also used more broadly for concentrated seasonings made from different ingredients. In a koji-based process, enzymes produced by the koji mould help break proteins into smaller compounds, including amino acids associated with savoury taste.

Mushrooms contribute their own earthy flavour; dried shiitake can add further savoury character. The result depends on the ingredients, the process and the final salt level, so “mushroom garum” should not be taken to mean that every formula tastes or behaves exactly like fish sauce.

From ancient garum to modern plant-based sauces

Ancient Roman garum was generally fish-based. Modern chefs have expanded the idea to other ingredients, including mushrooms and vegetables. Noma Projects describes using koji to help break down proteins and develop savoury depth in its own controlled garum work. That provides useful culinary context, but it does not independently verify a different home recipe or its storage safety.

Read the original context from Noma Projects’ explanation of garums and its article on koji and garum.

Food-safety note: do not treat the original long ferment as a validated recipe

The supplied draft gave a 16% salt formula, a 60°C holding temperature and a 60-day timeline, then described the result as safe and shelf-stable for years. The source material does not provide a validated process for that exact mushroom, koji, water and salt mixture. Those figures alone are not proof that the finished sauce is safe, pasteurised or shelf-stable.

We have therefore removed the step-by-step long-fermentation formula and its shelf-stability claims. Do not use the old formula as a home-preservation protocol or store the result at room temperature on the strength of salt percentage and temperature alone. Food-preservation guidance stresses tested formulations and product-specific safety controls; a qualified process authority would need to validate a long-fermented product of this type.

For background, see the FDA’s HACCP principles and the National Center for Home Food Preservation’s guidance on tested fermentation recipes. These are general preservation principles, not a validation of a mushroom-garum recipe.

What the controlled long-fermentation method involves

In professional garum production, koji, salt, water, raw materials, controlled temperature and monitoring work together as a process. Noma Projects describes its own use of a warm environment around 60°C to accelerate enzymatic activity in its specific method. That is not a universal instruction to hold any homemade mushroom mixture at 60°C, nor does it by itself establish a safe storage life.

If you want to explore long-fermented garum, use a published, process-specific recipe from a qualified source and follow its exact conditions. Do not improvise the salt percentage, ingredient proportions, temperature, container, or storage method. We are not presenting an unvalidated mushroom mixture as an at-home shelf-stable ferment here.

Ingredients for a cooked mushroom umami sauce

This is the practical alternative in this guide. It is a cooked seasoning sauce, not a fermented garum, and it does not rely on live koji enzymes.

Cooked alternative · about 45 minutes

A 45-minute mushroom, shiitake and soy sauce

This quick reduction adds savoury depth to broths, sauces, vegetables and beans. It is not a fermented product, and it should not be stored like shelf-stable fish sauce.

1. Combine: Put the chopped mushrooms, soy sauce, kombu and water in a saucepan.
2. Simmer: Bring to a boil, then lower the heat and simmer gently for about 35–40 minutes, until the liquid is noticeably reduced and the mushroom flavour is concentrated. Keep an eye on the pan and lower the heat if it reduces too quickly.
3. Finish: Remove the kombu. Stir in the dried shiitake powder and steep for five minutes, then strain through a fine sieve if you prefer a clear sauce.
4. Cool and store: Divide into a clean, shallow container, cool and refrigerate promptly. Use within three to four days as general cooked-leftover guidance, or freeze in small portions. Do not treat it as shelf-stable.

Seasoning note: Soy sauce varies in saltiness. Start with a small amount of the finished sauce in a dish, taste, and adjust rather than adding a large quantity at once.

Allergens: Soy sauce contains soy and may contain wheat; check the product label if cooking for anyone with an allergy or intolerance.

Why the quick sauce is not the same as garum

Soy sauce contributes an already fermented flavour, while this recipe extracts and concentrates flavour through cooking. It does not reproduce the enzymatic breakdown that happens in a properly controlled koji-based garum process. Think of it as a convenient vegetarian seasoning alternative, not as an instant version of a 60-day ferment.

• For cooking tonight: use the mushroom–soy reduction as a seasoning sauce.
• For koji-based garum: study a qualified, process-specific method and its safety controls; do not assume a ratio or temperature transfers to a different formula.
• For storage: refrigerate the cooked sauce promptly and use it within three to four days, or freeze it.

How to handle and store the cooked sauce

Move the sauce into a clean, covered, shallow container and refrigerate it promptly rather than leaving the pan on the counter. USDA FSIS advises refrigerating cooked leftovers within two hours (one hour when the ambient temperature exceeds 90°F/32°C) and using most leftovers within three to four days. That is general leftover guidance, not a tested shelf-life study for this exact recipe.

Source: USDA FSIS food-safety basics.

What to remember

• Mushroom garum is a controlled koji-based process, not just mushrooms steeped in salty water.
• A 16% salt calculation and a 60°C setting do not, by themselves, validate a particular home ferment or its shelf life.
• The cooked mushroom–soy sauce is a separate, quick alternative; refrigerate it promptly and use within three to four days or freeze it.