TToday’s recipe is the pinnacle of zero-waste cooking. If all else fails and you have a compost bin full of vegetable scraps, they can still be preserved by turning them into garum, an ancient Roman sauce traditionally made from fermented fish and more recently other meat and vegetable products and even peels. It is similar to Worcestershire sauce, fish sauce and soy sauce, and is used in much the same way to season and add incredible depth of flavor.
Garum has been repopulated and reinvented in recent years by fermentation experts such as: Sandor Katz and Noma’s fermentation lab. Experimentation has led to all kinds of garums made with both animal products and vegetables, using everything from eels and emu to coffee grounds and compost. When I spoke to Katz about making my own, he suggested being selective with my scraps to create a more distinctive, better-tasting end product — celery root and onion skin garum, for example, or leek-top garum.
My recipe is an adaptation of a recipe from Katz’s latest book, Fermentation trips. It was made by Patrick Marxera food waste pioneer in Zurich who makes garums from restaurant waste and sends it back to them to cook with.
Veg-scrap garum (AKA compost sauce)
Garum is an umami flavor bomb that has been used in cooking for centuries. It was especially popular in ancient Roman cooking and was used in everything from lamb stews to salad dressings. Admittedly, fermenting your own garum is a labor of love, not least because of the time it takes. I recommend storing leftover vegetables in the freezer until you have enough to make this recipe for large batches. Use it as soy sauce to add salt and umami to any dish.
As Katz writes in his book, Marxer incubates his garum at 60C (140F) to protect it from bacterial development, but Katz suggests the fermentation at a lower temperature is an “improvement.” Processing at a higher temperature will speed up the process, while a slow fermentation, such as garum was traditionally made, can result in a deeper flavor. To protect the sauce from harmful bacteria, Katz suggests using a higher salt ratio of 6%; Noma, meanwhile, suggests a higher salt ratio of 18%, so I’ve gone for a safe middle ground of about 10% here. Katz also recommends stirring the garum daily, at least to start with, to prevent mold growth on top; after a month or so, when the main active part of the fermentation process is over, stir it less often, maybe once a week. I made mine with two types of juice pulp donated to me by a local juice bar. The juicer grinds the vegetables perfectly, ready to make garum.
500 grams of vegetable shreds (e.g. onion peels, vegetable peels, coffee grounds)
300 g koji – you can get this fermented rice or soybean mix at Asian supermarkets, health food stores and online
160 g sea salt
Chop or pulse the vegetable shreds until finely chopped. In a large clean pot or bucket, combine the koji and sea salt and cover with 800 ml of cold water. Decant into Kilner jars or similar with the lid on but not snapped shut to allow any gases to escape. Store out of direct sunlight in a low cabinet where the temperature is relatively stable for at least eight or nine months and ideally a year. Stir daily at the beginning of the fermentation process to prevent mold from forming on the surface, then less regularly as the fermentation stabilises. When the garum is at its best, store it in clean bottles or jars, seal it and use it within two years.