posted by Josh Evans
A couple weeks back we found a recipe in Sandor Katz' The Art of Fermentation for 'Conserva Cruda di Pomodoro', a type of raw tomato paste that is preserved through moulding instead of cooking. Now, tomatoes aren't the most Nordic thing in the world (though you can find them here if you try), but we were interested to see how it works and if the technique could be adapted to other substrates.
We squeezed 4kg of tomatoes into a bucket, covered it with a cloth and left it out to ferment.
The recipe told us we'd start to get some bubbling, and then after a few days a white mould would start to form on the surface. Twice a day we stirred the mould back into the liquid/pulp mixture, until the bubbling subsided and it had a nice ripe smell.
The smell was the real surprise – tropical, like overripe mangos and passionfruit. And something a bit animal about it too.
Once the moulding was done we strained out the liquid, passed the pulp through a tamis to separate the flesh from the skin and seeds, and used a superbag to squeeze out any remaining liquid. We were left with 3kg of peach-coloured, tropical-fruit-smelling aromatic juice, and 150g of a bright red, homogenous paste almost fatty to the touch. A yield of about 3.75%.
We hung the paste in cheesecloth overnight to get out any remaining moisture, then added in 8% salt by weight to stop any mould activity. The original recipe calls for 20% but we figured we could do with lower.
What we have now is a concentrated, 'raw' tomato paste that we can use to season soups, sauces, and other dishes with an intense, fruity flavour. The paste itself has surprisingly little taste on the tongue; most of its merit is the aroma.
The juice also provided a new ingredient to play with. It has a beautiful translucent colour when it separates, and tastes surprisingly sour. When reduced it takes on a host of funky, meaty, grill notes that aren't usually present in regular tomato sauce. Dehydrated, it turns into a potent, sour and savoury dry paste.
We have been thinking of ways to take this process further with ingredients more commonly Nordic. Cucumber came to mind, for its high water content and natural sweetness when juiced.
This time we experimented with available liquid in regulating the moulding process. In one bucket we blended the cucumber to a thick slurry; in the other we left it chopped in chunks. After a couple days, the blended one looked and smelled quite similar to the tomato, while the chopped one had become yellow, slimy, and definitively putrid. So the moulding process seems to be dependent on the liquid phase.
A later trial with raw onion purée started out promisingly but quickly turned rancid with an overwhelming chemical pungency, like ethyl acetate mixed with garlic. Perhaps it wasn't quite liquid enough; and the natural anti-microbial properties of alliums might have had something to do with it as well.
After the same process of straining, scraping, and superbagging, we were left with a little ball of flecked green paste. Again intensely aromatic; and again, almost tasteless. What we really want to know is, what type of mould is it? We kept them in our mould room, so maybe types of Aspergillus from the koji? We are fascinated by moulds and there is so much more to know.
To try to extract that incredible aroma, we immersed the paste in 75% ethanol. Perhaps a tincture can give us access to that tropical fruit smell in a more versatile form.