Hongeo-hoe (Sliced Fermented Skate)

Variations

• Hongeo samhap: fermented skate, boiled pork and aged kimchi eaten together in one mouthful, the Jeolla way of serving it — and what the photograph shows. Fatty pork and sour kimchi blunt the ammonia, so the combination is less a matter of taste than a buffer. With makgeolli alongside it is called hongtak.
• Hongeo-ae-guk: a soup of the liver and young barley shoots. Made with unfermented skate too.
• Hongeo-jjim: steamed and dressed. Heat drives a good deal of the ammonia off, which makes it the easier way in for a first time.
• Fermented less: plenty of places sell skate held only three or four days. Heuksan-do palates prefer it a few days longer, and the same fish at different stages is effectively several dishes.
• Fresh skate sashimi: it is also eaten unfermented — clean, mild and with none of this page's chemistry in it.

Tips

• This runs opposite to fermentation basics. That guide calls fermenting "rigging a competition" so lactic bacteria win, and says the safety of a ferment comes from the acidity dropping fast. Skate becomes safe because the pH rises. A pH of 9 is as uninhabitable for spoilage organisms as a pH of 4.
• All three of that guide's levers behave differently here. There is no salt concentration to set, because no salt goes in; the temperature band is chosen for urea-splitting bacteria rather than lactic ones; and instead of keeping air out you deliberately leave it open. Pressing everything under a liquid, which that guide calls the whole anti-mould strategy, is the way to ruin this.
• The guide's failure list is this dish's doneness test. "Slimy, with a rotten smell → failed" is written there, and here a sharp smell is exactly what you are waiting for. The distinction is real though: ammonia stings the nose, spoilage smells sour and sweetish.
• Ganjang-gejang is the exact counterpart. That page tells you that if there is any ammonia smell, do not use it. In a crab that smell means it has gone off; in skate it means it is ready. Same molecule, opposite meaning — the difference is where the nitrogen came from.
• It only works with skate and ray. Carrying urea in the flesh is a trait of cartilaginous fish. Leave mackerel or flounder the same way and it simply rots.
• It is not stinky tofu either. That smell comes from microbes breaking down soy protein, and it needs a brine to do it in. Nothing is added here at all.
• Ammonia dissolves readily in water. If your mouth burns, hold a mouthful of water or makgeolli; it settles far faster than waiting it out the way you would with chilli.
• Buying it already fermented is a reasonable choice. The process is sensitive to temperature and time, and a failure here is not merely unpleasant but unsafe. It is the same judgement stinky tofu makes in buying its fermented bean curd.