How to make Fish Hydrolysate

We are keen on using resources -especially those that tend to belong to the waste stream- that are readily available in the local environments where we work. An important part of plant health is nutrition and so we look for solutions on how to convert organic matter into fertilizer which plants can actually absorb. Such processes involve for example: composting, vermi-composting, fermentation and collection and reproduction of local microorganisms.

In this post we will focus on the production of Fish Hydrolysate, of which the main ingredient is fish, an abundant resource in the Sunshine State. Fish Hydrolysate is often confused or wrongly called Fish Emulsion. The difference between these two processes is that one (Fish Emulsion) uses heat to break down the solids and the other uses fermentation (Fish Hydrolysate). The advantage of making Fish Hydrolysate is that the majority of amino-acid chains and fats remain viable and available for fungi to decompose and convert into plant food, it is a cold process that helps break down all the parts of a fish without denaturing them.

As the name suggests, Fish Hydrolysate is a process that uses water as a medium to extract the desired components. A source of sugar is used to kick start the fermentation process in which different kinds of microorganisms will reproduce and break down the fish. We also add LAB, which provides the solution with enzymes and bacteria which will break down the organic matter as well.

Fish Hydrolysate will provide nitrogen, trace minerals, potassium, amino acids, proteins, fatty acids, carbohydrates to plants and animals.

If you are interested in learning more about these processes we suggest researching KNF (Korean Natural Farming). This methodology of farming is well known in Japan and Hawaii and suggests ways to solve problems while farming without the use of agrichemicals. Another good author on topics related to organic agriculture in Latin America is Jairo Restrepo.

Although KNF generally provides you with a recipe, its teachers also explain that you have to work with what is available, therefore exact measurements are not necessary but recommended.


A simple way to make Fish Hydrolysate is in a 5 gal or 55 gal drum. A 5 gal bucket may be enough to feed a small garden for a couple of months, a 55 gal drum will provide enough fertilizer for a small homestead or farm. If this is your first attempt start out small and give it a try with a 5 gal bucket.

You will also need:

  • Non-chlorinated water (If you are using city water let it sit for at least 24 hours, another option is to collect rainwater). You will need 3 parts water to 1 part fish approximately.
  • Meat grinder, hatchet or meat cleaver.
  • LAB. Around 100ml for a 5 gal bucket. You may also use liquid from a lacto ferment or kombucha or whey, too, in this case use a cup.
  • Molasses or brown sugar. You will need 3 parts fish to 1 part sugar. We use 1 cup molasses per 5 gal bucket. Sugar is not a necessary ingredient but it helps kick start the fermentation and reduce the initial smell. We consider that molasses is a commodity in the US because it is so expensive. Therefore, we use it sparingly. If you have sugarcane and a sugar cane press we highly suggest using sugar cane juice. You may also ferment sugarcane stalks chopped in small pieces to extract the sugar.
  • Fresh fish carcasses, guts, skins, whole fish (If you cannot make the Hydrolysate the same day you get the carcasses freeze them!)
  • If you are close to a pristine forest collect some old leaf litter which shows signs of mycelial activity. Remember to always return to the Forest what you have taken from it. Next time bring some Fish Hydrolysate back.
  • A piece of mosquito screen or net to cover the bucket
  • A shoe lace, rope, tie or string to tie the screen

The process

  1. Chop or grind the fish, carcasses and guts as finely as possible. When we don’t have a grinder we try to chop pieces that are around 1″x1″. Work on a clean (not disinfected, just clean) surface.
  2. Place fish in the bucket.
  3. Add molasses.
  4. Add LAB.
  5. Fill with water and leave about 4 inches of headspace.
  6. Cover with screen and tie it tightly around the brim. The benefits of aerobic fermentation versus anaerobic is that the end product renders more microbiological variety and diversity. If a fertilizer is going to be used both for drenching as well as for foliar application it is within your interest to have both kinds of microorganisms present in your ferment, you can achieve this through aerobic fermentation.
  7. Stir concoction at least once a day for the first couple of weeks. This will ensure that no mold appears on the surface and that the fermentation remains vigorous. After the ferment stops bubbling intensely and after 2 weeks have passed you may stir more infrequently. If black mold or hairy mold appears, you may use the mix to inoculate your compost system. The mix may be contaminated.

    If you don’t take the aerobic route another option is to place a plate with weight in the bucket which will keep the solids submerged. Stirring is still necessary but not as frequent, however the process may extend as it will take longer to decompose the fish. Last but not least you may make Fish Hydrolysate anaerobically by building a water seal or using a check valve and sealing your bucket tightly with a lid (This is great if you need to step away and cannot stir, but the end product will be slightly different).

You will know your Fish Hydrolysate is ready when it has a pleasant fermented smell (maybe similar to sweet fish sauce?) and the majority of the solids have dissolved. We recommend straining it to use with a backpack sprayer. KNF generally proposes to use these types of compounds in a ratio of 1:1000 or 1:500. We recommend testing your final product with different dilutions to determine the right amount.

Fish Hydrolysate can be used as a soil drench, foliar spray, compost inoculant, compost tea inoculant and fodder supplement. Let’s get fishy!

Cutting the fish
Pieces of fish in the buckets with molasses
4 week old Fish Hydrolysate
Unfinished Fish Hydrolysate, fermentation must continue

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