October 2014

Tacit Knowledge

 Len Fisher
One prominent theme for a meeting on Food and Communication must surely be the notion of tacit knowledge – that is, know-how that is only, and sometimes can only, be passed on through direct experience. A recent example from the world of science was described in the journal “Nature” (Vol. 514, pp. 139 – 140 (2014)). It concerned measurements of the quality of sapphire, now used to make laser mirrors. Russian scientists were professing very high precision that Western scientists were unable to match, and accusations of false claims abounded.

The reason was simpler. The sapphire crystals in question were suspended from thin threads, which the Russian scientists said were coated with a “fatty film”. No fat that the Western scientists tried worked. Then it came out that the film was produced by one of the Russian group running the thread across the bridge of his nose before attaching the sapphire. When Western scientists tried the same trick, they were finally able to replicate the Russians’ ultra-precise measurements.

Tricks abound in cooking. One that has a rather similar basis is always to save some used frying oil, and add a little to fresh oil before using it. This helps to prevent fish and meat from sticking to the bottom of a non-Teflon coated frying pan, because the breakdown products from the previously heated oil attach themselves to the metal to form a thin, anti-adhesive, film. There must be many similar tricks around, often unmentioned in recipe books. It will be good to learn about some of them at Oxford 2015.

Update Oct 20, 2014: Peter Hertzmannn tells a nice story about tacit knowledge when it comes to confiting duck parts: “When I learned to confit duck parts in the Dordogne, I was required to turn the meat in the fat with my bare hands, i.e., to assure that the fat would not get too hot. That temperature was about 65 °C.

The first part is the tacit knowledge; the last part is Peter’s scientific interpretation which, as so often in science, comes a posteriori rather than a priori. Peter goes on to say: “I think the tacit knowledge aspect works for good and bad. A lot of what is taught is based on misunderstanding, and that it must be true because “that’s how I was taught.” It was a problem when I worked with surgeons and now I see it with chefs and worse with cookbook authors [see Oliver Sachs’ “Uncle Tungsten” for a wonderful example from the chemical industry}.

By way of example, if you look at old recipes for what today we call braising, only a little or no liquid was added to the pot. Now I see entire books devoted to braising where the last step before cooking is to cover the item to be cooked with liquid. To me this is simmering, not braising.”

I agree, and hope that the whole subject of tacit knowledge gets a good airing at Oxford 2015.