To fully appreciate the contents of this article, we recommend first reading our article on the science of tempura frying oil and best practices when serving tempura. To learn more about tempura, you can begin at our series.
In the world of foodies, influencers and social media, everyone is always chasing after the hottest food trend or the must-visit restaurants. People fuss over the awards that a restaurant wins or prestige that it holds, flaunting how many Michelin stars a restaurant has earned, how hard it is to book and even its tabelog rating. And we totally get it, judging a restaurant like this gives us a certain level of assurance and guarantees that we won’t have a bad experience, a concrete number that we can hold on to. Afterall, who wants to waste their money on a bad restaurant? It’s even reached the point that some influencers hesitate to share their latest discovery and it can make the restaurant impossible to book. We are even forced to use keywords (that we absolutely hate) to attract people to our websites. You’ll see many of our article titles starting with “Three Michelin Starred Recipe for….” or “The Ultimate/Best/Complete Guide to……”
The tempura restaurant we’re covering in today’s article is one such restaurant. Tempura Kusunoki (天ぷらくすのき) has been making the rounds on social media as influencers post photos and write articles phrasing it as revolutionary, changing the way we think of tempura. What’s made it even more controversial is that it received a tabelog award yet was not acknowledged by the Michelin guide at all! It was so popular that he started charging reservation fees which increased the further ahead you booked, meaning that if you booked 6 months in advance you’d have to pay around 200 000 yen to eat there.
This leads us to several questions we’ll be answering. What makes Tempura Kusunoki special? What is the science behind what he does? Before ultimately covering tempura Kusunoki’s Recipe.
What makes Tempura Kusunoki special?
Hand served tempura with no excess oil
Tempura Kusunoki’s biggest surprise factor it that the owner and chef, Tadashi Kusunoki (楠忠師), serves each piece of tempura with his bare hands, presenting it to the customers as though it was a piece of nigiri. You’d typically expect tempura to be too hot to handle having just been removed from the oil but once consumed, it is crisp on the outside, and perfectly warm on the inside. He claims that this is because his tempura is so perfectly fried that it does not hold onto any excess oil, which he backs up asking customers to observe the tempura paper placed in front of them, that maintains pristine throughout the whole meal as there is no oil for it to absorb from the tempura. This is incredible as even the most famous tempura restaurants replace the guests’ tempura paper every few pieces as it slowly gets saturated with oil that drips from the pieces of tempura.
Kuji sand iron pot
It’s also immediately obvious to anyone who has dined in his restaurant that his setup is quite different. While most places use a huge copper or gunmetal pot filled with oil, you’ll see that he uses a small sand iron pot (久慈砂鉄鍋) manufactured in Kuji, Iwate. It’s a pot that is no longer manufactured or available for sale, but hints to us that he follows the train of tempura principles based on Kokichi Kawabe’s (川部幸吉) book titled ‘The Secrets of Tempura’ (天ぷらの奥義).
This pot is extremely rare to find and is much higher quality compared to other equivalent cast iron pots you may find on the market today that skimp on material to cut down costs. It was made in an era when sand iron deposits where mined to supplement Japan’s domestic iron production and is said to be the same deposits in the foothills of Kuji, Iwate prefecture, where the iron used to make the sword of the first feudal lord of Sendai, Date Masamune was obtained.
Seasoning before serving
Lastly, most tempura places leave the seasoning of the tempura up to the customer, whether that be providing them with grated daikon in tentsuyu that they can dip their pieces into, or salt and lemon that they can add for themselves. Instead, just like in a sushi restaurant, Tadashi Kusunoki believes that the chef himself knows best the perfect seasoning for each individual piece of tempura, and sprinkles on the appropriate amount of salt before serving it to the guest.
His preference is a special salt known as Aguni salt (粟国の塩) from Okinawa. It is made by pumping sea water into the top of a special building that contains 15000 bamboo branches hanging from the ceiling all the way to the floor. The building itself has numerous gaps built into the walls that allow the sea wind to pass through the building. The sea water is allowed to flow through the bamboo branches hung from the ceiling and drip onto the floor, all the way evaporating with the help of the sea wind, creating a concentrated salt solution. The salt solution is then reduced with a wood fire until the nigari can be removed and then left to dry naturally for 2 weeks before the salt can be harvested.
The science behind Tempura Kusunoki’s oil-less tempura
So what’s his secret to oil-less tempura? Unfortunately, Tempura Kusunoki has not been as generous as Tempura Niitome with his information, but to a trained eye it’s easy to figure out.
His approach to tempura is to use every trick available to him to reduce the amount of oil absorbed by tempura. Interestingly enough, from our understanding of how he speaks, be it in interviews or in person, we actually doubt he understands any of the science we hypothesize is underlying his technique, and that he has simply developed his skills through trial and error by himself.
The hydrophobic nature of oil
Most deep frying occurs at temperatures above 150°C. This means that when a piece of food is dropped into hot oil, the moisture in the food immediately rises to boiling point. Here, the steam produced from this reaction has nowhere to go other than to push through the batter due to the build up of pressure to form crevices through which it can escape. This is why the food is almost immediately engulfed with streams of bubbles after it submerges in hot oil.
As we mentioned briefly in our article on the science of tempura frying oil, cooking oils are hydrophobic in nature and do not mix with water, which means that a fresh batch of oil is not ideal for deep frying. This is because the bubbles that engulf a piece of food being fried actually act as a layer of steam through which the oil cannot penetrate, causing food deep fried in fresh oil to actually spend very little time spent in contact with the oil, and the majority of the time steaming in its own juices.
As oil continues to be heated up and cooled down through several rounds of deep frying, the oil breaks down into different compounds, some of which are emulsifiers. Emulsifiers are compounds with both hydrophilic and lipophilic parts in their molecular structure which help oil and water mix together. They play an important role in the world of cooking and you’d most likely recognise their role in sauces such as hollandaise and mayonnaise. As more emulsifiers accumulate in the oil, it causes the oil to more easily mix with the steam from the bubbles and come into direct contact with the food. Contrary to popular belief, this is why deep frying oil is actually at its prime after it has gone through one or two rounds of frying and not fresh out of the bottle.
However, at Tempura Kusunoki, Tadashi Kusunoki actually takes advantage of this fact by changing the oil frequently enough to prevent it from degrading and to prevent the emulsifiers from accumulating. By doing so, his tempura absorbs far less oil compared to other chefs as he tries to preserve the hydrophobic properties of his cooking oil, preventing oil from being absorbed into his tempura.
Why don’t other chefs do that? While it’s not uncommon for the frying oil to be changed during the course of a meal, changing the oil more frequently is usually cost prohibitive, especially at restaurants that use pure sesame seed oil. Other than the fact that Tempura Kusunoki is the most expensive tempura restaurant as of writing, he is also able to do so because of the Kuji sand iron pot mentioned above that he uses.
Iron has lower heat conductivity relative to other common metals used in cooking utensils, thus reducing the amount of heat control over the oil he has. However, iron makes up for this by having high heat retention, allowing him to maintain a stable oil temperature when pieces of tempura are added in. If you were to compare two pots that can the hold the same volume of oil, one made from sand iron and the other made from copper (a common material used for frying tempura), the temperature of the oil in the copper pot would drop much faster compared to the sand iron one if the same amount of food were added in. Most restaurants would make up for this difference by using a much larger copper pot that can hold a much larger quantity of oil to achieve the same stability. This is why most commercial grades of tempura pots are at least 35 cm in diameter and above, with most averaging above 45cm.
At Kusunoki, a ‘non-commercial’ sized tempura pot is used at only 30 cm in diameter, but since it’s made from sand iron, he still has the same level of temperature stability he would have from a conventional setup. What’s more, a smaller pot means using much less oil, which he can then replace frequently without worrying about cost.
From our experiments, there also seems to be a possibility that the sand iron pot reduces the rate of oil degradation. Due to its high heat capacity, the oil in an iron pot stays at a relatively constant temperature and does not fluctuate as much compared to a copper pot. While high temperatures of any sort degrade cooking oils of any kind, we feel that a constantly high temperature might be less damaging compared to oil that is constantly being cooled and heated up over and over again.
The outward pushing force of steam
Another trick that Tadashi Kusunoki uses to reduce the amount of oil absorbed by his tempura sounds counterintuitive- after frying a piece of tempura, he dips the tip of the tempura back into hot oil for a short period of time, then only moving it to a tray to rest. He claims that this works because the temperature difference between the hot oil and the tempura causes the oil in the pot to pull any excess oil away from the tempura. To re-emphasise again, I think it’s obvious to anyone who knows anything about how liquids behave in a temperature gradient that this is factually incorrect. It is impossible for hot oil to pull cooler oil away.
Instead, we propose two possible explanations to what is occurring. Firstly, dipping just the tip of a piece of tempura into hot oil will cause any excess oil to be pulled by gravity towards the tip. Under normal circumstances, the oil would accumulate at the tip and either drip off or be absorbed into the tempura. However, by dipping the tip back into hot oil, it quickly heats up the food underneath the batter back to boiling point, causing the moisture in the food to be released as bubbles of steam. As the steam escapes through batter, it pushes away any excess oil that may have accumulated at the tip, reducing the overall amount of oil in the tempura. Secondly, and this explanation is less probable, the brief re-immersion in hot oil might help to seal the exterior of the tempura, preventing further oil absorption.
Whatever the case, from our testing, dipping the tip of the tempura back into the hot oil for a brief moment is more effective at removing excess oil compared to simply allowing excess oil to drain on a wire rack.
Gluten development as a barrier to oil absorption
Most tempura restaurants make a large bowl of batter initially, before adjusting the consistency of tempura batter on the fly as they go. The batter is then refreshed once it’s no longer in its prime. At tempura Kusunoki, a large bowl of batter is not made all at once, but instead a small amount of egg and water mixture poured into a bowl at an angle, on which a large amount of flour is sieved. He then whisks this together to produce a small amount of batter, adding in more liquid mixture or pushing in excess flour from the sides of the bowl to make more batter. What this causes is a greater amount of gluten development as the batter is not refreshed as often.
This is obvious from pictures of Kusunoki’s tempura you might find on the internet. The pieces of batter coating the food appear thicker and more opaque with a slightly wavy pattern, rather small thin shards with a semi translucent and glistening appearance, hinting at the higher amount of gluten.
From our testing, it seems like a fine balance is being achieved here. If a batter has more gluten development, it may indeed absorb less oil during frying. This is because the gluten network formed in the batter can create a barrier that reduces the penetration of oil into the food. Additionally, the gluten network can help retain moisture within the food, which can also reduce the amount of oil absorbed as water and oil do not mix. However, if too much gluten is developed, the resulting tempura would not only be chewy, but soggy as too much moisture would be trapped inside the tempura and absorbed by the oil.
Temperature control and serving procedure
Compared to Niitome’s lower temperatures, Kusunoki famously fries his tempura at around 200°C. This is way higher than the conventional 170°C to 180°C. At this temperature, we have found that the batter solidifies much faster, quickly forming a crust that prevents excess oil from penetrating the food.
From careful observation, it’s also slightly misleading to say that his tempura comes out of the pot with all excess oil completely removed. That just isn’t possible. It’s like saying that you can submerge something in water without getting it wet. In actual reality, many of the pieces of tempura he serves are first placed on a tray lined with oil absorbent paper to cool to its optimal temperature first, before being sliced to size on a chopping board, then only served to customers by hand. At this point any excess oil that would have dripped onto your tempura paper would have been absorbed by the lining of the tray.
Ultimately, none of the techniques mentioned above alone remove a huge amount of excess oil from a piece of freshly fried tempura. However, by combining the small effect of all three techniques it’s possible to achieve a noticeable reduction in the final oil content of the tempura, leading to his characteristic tempura that leaves no visible trace of oil when placed on a piece of tempura paper.
Tempura Kusunoki’s Recipe
To prepare his flour, Tadashi Kusunoki sifts his flour in a wooden box at -20°C to help decrease gluten formation in his batter. This is because wood is a semi-permeable material that will still allow excess moisture to evaporate from the flour and escape. While that might sound counterintuitive as he makes a batter with higher gluten development than other restaurants, it’s easier to suppress gluten development in flour before mixing the batter, before controlling the process yourself through whisking and adding more flour. You’ll notice he uses a much higher temperature to freeze his flour compared to other chefs (like Niitome at -60°C) as it is a much more achievable temperature in a home freezer without the need for specialized equipment.
He uses a brand of flour called Takaragasa Gold (宝笠ゴールド) by Masuda flours (増田製粉所) with a protein content of 7.6%. It can be hard to buy outside of Japan and so Nissin’s Violet flour is a valid alternative. For his final course, he serves a tendon dish using Mineasahi rice (ミネアサヒ) from Aichi prefecture cooked in a Nagatanien clay pot, which he sometimes changes with a Kumoi Kiln clay pot. You can learn more about different varieties of rice in Japan in our series on rice.
