This recipe has been constantly updated over the years with the latest update at the very bottom of the article. Accompanying articles such as wild vs farmed unagi and the traditional liver soup recipe served alongside this have also been written. To learn how to fillet live unagi, read our recipe on simmered sea eel which follows the same filleting technique.
Japanese Grilled Freshwater Eel on rice
Unagi, or Anguilla japonica (日本鰻 ), is the name of the Japanese freshwater eel that’s grilled over a charcoal fire whilst being coated in sweet soy sauce glaze, a style known as kabayaki (蒲焼). It’s always been one of my personal favourite dishes and it’s what I’d usually order in a restaurant when I feel like having something soulful. Seeing how expensive a bowl of Unagi with rice usually costs, I wanted to see if it where possible to make yourself and this post explores that. Other than its usual preparation method, Unagi is sometimes grilled with salt alone and served with wasabi, a style known as shioyaki (塩焼き).
Today, Unagi is not only eaten all year round, but also throughout the entire world, so much that it has become a staple dish that one expects in any Japanese restaurant outside of Japan. This in return, has caused a decline in freshwater eel stocks to almost endangered levels. To counter the problem, the Unagi industry has switched to commercial farming of freshwater eel to meet the demand of various restaurants around the world. This solution however has not stemmed the problem of declining wild stocks as the current eel breeding technology is in its primitive stages and thus eel farming requires baby eels to be caught from the wild before being raised in captivity. While Unagi live their whole adult life in freshwater, they actually return to the sea to spawn and lay eggs. Read more information on wild vs farmed eels in Japan.
Unagi in Japan is typically eaten on the midsummer day of the Ox (土用の丑の日), which falls on the 12th day before the start of autumn, as the protein and vitamin rich Unagi was said to provide strength and energy to workers for the coming year. As almost all of the eel eaten in Japan today is farmed, some farmers are trying to farm eel in a way that mimics wild in as close as possible as wild eel is supposed to have superior flavour due to its fat composition. Unagi naturally feel on plankton during the summer on order to grow as quickly as possible, before slowing down during the autumn in order to start storing fat. In the winter, these eels start to hibernate. These farmers try to mimic the seasons as close as possible in their farming ponds, even going the extra mile to store the Unagi in barrels which are placed in ice-cold streams during the winter months to facilitate hibernation. This process is repeated over several seasonal cycles before the eels are harvested.
Unagi itself has an intrinsically rich and strong flavour, which is why the kabayaki style by which it is traditional prepared is so suitable for it as the mixture of caramelised sweet sauce pairs very well with it. The methods for preparing Unagi is so ingrained in Japanese culture that the recipe for making the sweet sauce is kept secret from restaurant to restaurant. While the base of the sauce is said to be made from a mixture of soy sauce, sake, mirin and sugar, the exact proportions vary from restaurant to restaurant, with the head of the restaurant only passing down the secret recipe through the family line. These particular restaurants specialize only in the preparation of Unagi alone and the pot of sauce bubbling away in the kitchen is their most prized possession. This is because the pot of sauce in each restaurant is never allowed to run dry, but is constantly topped up everyday when it starts running low. This causes the flavour to concentrate overtime and the remaining of the previous batches sauce are mixed into the new batch and allowed to slowly caramelise again. It is said some of these sauces have been kept going for over 5 generations and well over 100 years, never being allowed to run dry. In addition to this, some restaurants dip the entire skewers of Unagi into the pot of sauce between periodically while grilling, compared to brushing the sauce unto the Unagi on this grill. This means that some of the juice from the Unagi is mixed into the sauce everyday. Having been repeated everyday for over 100 years, causes each pot of Unagi sauce to develop its own individual complex flavour.
The method for preparing Unagi is also unique compared to other fish. In almost all other fish, the belly of the fish is slit open to remove the guts. In contrast, Unagi is prepared using the ikejime method (活け締め), which involves, driving a meuchi (目打ち) or nail directly through the hindbrain of a live eel, which causes immediate brain death as well as paralysis. This method is superior because it immediately causes the muscles in the eel to freeze, preventing any further use of energy in the body. If you were to kill the eel using any other method, the body of the eel would continue to trash about, causing the consumption of energy in the form of adenosine triphosphate (ATP). As the eel can no longer breathe (because it’s dead), ATP is broken down through anaerobic glycolysis without oxygen, thus forming lactic acid which would give the eel a sour taste.
After dispatching the eel, the eel is filleted by cutting the down the backbone all the way down the entire length of the spine, splitting the eel open from top while leaving the belly untouched. This method is unique as it causes the belly to be positioned in the middle of the fillet, compared to conventional methods where the belly is cut in half. The innards are then scrapped away and the spine removed by inserting in knife underneath it and running it down the entire length of the eel. The eel is them skewered using bamboo skewers, ready for grilling.
The entire process of grilling Unagi is actually quite complicated. After being skewered, the Unagi fillets are grilled for a short period of time before being steamed. The initial grilling starts of the mallard reaction while the steaming that follows firms up the meat. The now firm Unagi fillet can then be deboned by hand. After deboning, the fillets is then dipped into the Unagi sauce and finished off on the grill before being served hot, with the skewers removed.
If we were to consider the preparation method for Unagi compared to other fish, it could be easily said that the Japanese overcook their Unagi as seafood usually only requires a short cooking time. However, this method of grilling, steaming and grilling actually creates a melt in your mouth texture. This is because the meat of Unagi is rather firm to start of with, and thus a fast cooking method such a pan searing would result in the Unagi becoming tough and rubbery. Furthermore the blood of the Unagi is poisonous if not cooked and thus this method of cooking ensures that the Unagi is safe to eat.
Grilled Unagi is more commonly served in a bowl, which is known as Unagi-don or Unadon (鰻丼) but can sometimes be served in a lacquered box, or Unaju (鰻重). It is mostly accompanied with a soup made from eel liver.
Japanese grilled Eel recipe
- 1kg of salt for cleaning the eel
- 500ml Water
- 500ml Soy Sauce
- 250g Granulated Sugar
- 250ml Mirin
- 200ml Sake
- 2 live Unagi, about 800g each
- Read a photo by photo instruction on how to prepare live eel. The method is the same as for sea eel, which is what is shown in the example.
- Kill the 2 live Unagi by hitting each Unagi on the head with a mallet. Alternatively, if you have a nail or meuchi (目打ち) and hammer, drive the meuchi down the back of the head of the eel to kill it immediately.
- After dispatching the eel, clean the eel by rubbing it with the salt, one handful at a time before washing off with water. The goal here is to remove as much slime as possible from the eel using the salt. This process requires a lot of salt. Repeat several times until clean.
- Reattach the eel to the chopping board if using a meuchi. Insert your filleting knife or debabocho (broad-bladed kitchen knife) right behind pectoral fin. and slide the knife along the entire spine to open the back.
- Remove innards by scrapping the knife along the eel.
- Remove the spine by inserting your knife under spine and running it between the spine and flesh.
- Place the fillets flat on the board and scrap the fillet gentle with the knife to remove any dirt.
- Wash gently with clean water.
- It is possible to use this recipe starting with pre-filleted eels but I have yet to see it sold anywhere unless ordered from a fishmonger in Japan. The taste of fresh eel is still the best.
- Cleaning the eel requires a lot of salt and scrubbing so it is best to wear gloves.
- Remember to cook the eel well as uncooked eel blood is poisonous.
- The innards of the eel should come out in one go if the eel is fresh.
- This recipe also works on catfishes.
Now a few years after this post originally went up, I’ve visited many many more unagi restaurants around Japan, including almost every Michelin starred unagi restaurant in Tokyo (of which my favourite is still Ookuniyamambei in Kyoto) and thus my understanding how unagi should be cooked has slightly changed. At higher end restaurants that specialise in eel, the sauce used to cook the eel serves to bring out the natural taste of the eel.
If you were to look at the recipe above, it doesn’t contain salt and has quite a high proportion of sugar, which is typical sweet sauce eel style recipe you’d get at your everyday restaurant. I’ve since learned that this is actually used to cover up the low quality eel that some of these restaurants use, and that better restaurants use a more balanced sauce that uses salt to even out the sweet edge, just enough for you to enjoy the eel flavour. And so following the same filleting techniques found here, the recipe for the sauce is as such:
- 250g of Mirin
- 250g of Sake
- 250g of Soy Sauce
- 150g of Sugar
- 10g of sea salt
Combine all the ingredients together in a saucepan, bring to a simmer and flambe. Reduce the sauce slightly.
The updated cooking times are now as such for a 800 eel before filleting.
- 6 minute grill on each side without any sauce, totalling 12 minutes.
- 10 minutes steam in a steamer.
- 2.5 minutes back on the grill each side after brushing the eel in sauce or dipping the eel in the sauce, totally 5 minutes.
- Repeat 1 or 2 more times.
The filleting technique used in sea eel (anago) and freshwater eel (unagi) is the same and also requires you to grasp the eel firmly as you pin it down on the board to nail through the hindbrain. As such, no salt is actually used to clean the slime off the eel as mentioned in the recipe above (where 1kg of salt is mentioned). However, doing so can be rather hard to do without any prior experience, and so coating your hands with hand before handling the eel still makes it significantly easier if needed.