Added on by Ben Reade.

posted by Ben Reade

I need to admit to an obsession: Basque salted anchovies. In 2010 I was lucky enough to see them being produced in the tiny Basque fishing port of Bermeo. The painstaking effort taken over each little fish produces a remarkable product. Let me explain the process.

Very fresh anchovies are layered in barrels with salt. Nobody will tell you exactly how much salt, but it's around 10-20% of the weight of the fish.  They are then left there for at least a year. During this time, osmosis draws water out of the fish until they are sitting in their own brine and equilibrium of salt concentration is attained. This causes the flesh to firm up and endogenous enzymes (hydrolases, proteases, nucleases, glycosidases, aryl sulfatases, lipases, phosphor-lipases [1] ) combine for autolysis of the flesh. The breakdown of the flesh is further facilitated by the enzymes in the anchovy's gastrointestinal tract – which is of course specifically designed for breaking down fish – to give it the rich umami taste typical of an easily digested protein.

After a minimum of one year, the anchovies are removed from the brine, and all by hand they are filleted, the skin is scraped off, and they are cleaned and trimmed. The polished fillets are then lined up on a clean towel, and rolled up.  The rolled-up towel is  put into a centrifuge which is spun to pull the water from the flesh. Selected by size, shape and quality, they are placed one by one into tins or jars, where they are covered in neutral oil. It was wonderful to watch these old ladies processing each delicious fillet with such care.

A Basque lady places anchovy fillets into tins (2010, Bermeo)

A Basque lady places anchovy fillets into tins (2010, Bermeo)

Although anchovies occasionally swim as far north as southern Scandinavia, they are not fished in any commercial quantity. But I wanted to make some kind of Nordic equivalent – what to do? The answer came like a rainstorm of fish – HERRING. There is a long history of salting herring for preservation in Scandinavia – but I wanted to end up with a product similar to that Basque fillet I had grown to know and love.

But there were problems. The best anchovies are cured with their entrails intact, so as to provide enzymes which facilitate the hydrolysis of the flesh from the inside out; but herring is a thicker fish than anchovy, which means it takes too long for the salt to permeate the guts and keep them fresh. So, the guts had come out, but when the guts come out, sadly so do their enzymes. Yet after reflecting on some of the lab's earlier work on umami arising from salt rich fermentations, it became clear that I could in some way replace the endogenous enzyme activity of the guts with exogenous enzyme activity from koji. And so was born the Koji-chovy. 


Curing koji-chovies, photo by Claes Bech Poulsen

Curing koji-chovies, photo by Claes Bech Poulsen

Herring Koji-chovies 

Now, take your herring, remove the head by breaking the neck backwards, and cleanly remove it with as much of the guts as possible. Leave the mandibular bone (or whatever it's called) to give the fish a good clean look. Make some barely koji (some pretty good instructions can be found here) and then follow this recipe:

2000g Aspergillus oryzae Koji of Pearled Barley

6660g Headless, gutless Herring (10kg whole weight)

1970g Salt

Mix 100g salt with the koji, and then stuff the fish with the koji, layering the stuffed fish with salt in between the layers.

Weigh the fish down and leave them at 2 °C until they are submerged in their own brine. Keeping the weight on top, leave them at ambient temperature for 1 year – although I impatiently started experimenting already after 6 months.
When you're ready to move to the next stage, fillet, debone, dry and cover in oil, or of course you can also marinate them. A successful marinade to try is a sprinkle of powdered juniper berries, crushed lingon berries and a dash of aged apple vinegar with some neutral oil. Vacuum seal them, and leave a couple of weeks to infuse.

So. To put things simply, these are bloody delicious, if a little bit salty. The saltiness is pretty easy to tackle, in the old Finnish method of leaving them to soak in milk overnight before grilling, but anyway, anchovies are salty and should be salty and our experimentation doesn’t stop here.

After the initial success of these prototypes my mind wouldn’t stop and we had to take the project further. This called for some of microbe friends to get involved. So I was able to lay my hands on two pretty special strains of bacteria, Tetragenococcus halophilus and T. muriaticus. The T. halophilus has been isolated from (get ready to gasp) Basque anchovies, and the T. muriaticus from a Japanese ferment called Shottsuru, a salt-rich ferment of squid liver. Tetragenococcus spp. are halophilic lactic acid bacteria which requires NaCl for growth and is tolerant of salt concentrations up to around 20%. At first, T. halophilus was the only species under the genus Tetragenococcus, yet T. muriaticus was proposed as a new species under the genus in 1997 [2]. Anyway, we have them both in the lab and are indebted to Eddy Smid, our fermentation and biotech guru at Wageningen University for sending us these fantastic and hard-to-find microbes. We now have these different versions slowly fermenting away downstairs, with our two cultivated strains of microbe, as well as wild ones for a control - we will see in time which emerges the winner.

And boy do we have a treat for the winning microbe. In March we were given this beautiful amphora by the talented potter Aage Würtz. My aim since first conceiving this pot is to pick a very successful ferment to inoculate the pot, so that the microbes can harbour their populations in the pourous ceramic walls and be forever perpetuated in the pot’s contents.

May this be a long and fruitful journey, and may herring continue to flourish in our oceans! 



1. Peter E. (ed) (1998) ‘Fish drying & smoking: production and quality’ Technomic Publishing USA.

2. Satomi et al (1997) 'Tetragenococcus muriaticus sp. nov., a new moderately halophilic lactic acid bacterium isolates from fermented squid liver sauce’ International Journal of Systematic Bacteriology p. 832-836