The Magical Umami of Koji: Explained!

I’m so chuffed to finally catch up with my talented friend, Yuki Gomi, a professional chef, teacher and cookery writer. I can still remember the taste of the delicious aubergine dish we made when I attended one of her wonderful Yuki’s Kitchen cooking classes in her home near my old haunt, Crystal Palace, about 10 years ago!

Since then, Yuki has gone from strength to strength, with her first book ‘Sushi at Home’ published in 2013 by Penguin, and her Japanese cooking expertise has reached many thousands of people. Yuki has been featured in the Guardian,  Monocle Weekly, Vogue magazine, and has been on The Chris Evans Breakfast Show, to name just a few!

Alongside regular classes at her home in South London, Yuki offers courses and private lessons at special events around the world and colleges such as the prestigious Leiths School of Food & Wine.

In this episode, we chat about:

  • The ubiquity of the soya bean in Japanese food
  • Bacteria, mould and heritage spores
  • What to do with the miso lurking at the back of your fridge
  • 5 core ingredients of Japanese cooking & what they all have in common
  • Why koji is magical ✨ & where to get your hands on some in London

Vanessa: So today I’m speaking with Yuki Gomi, who is a Japanese chef, food writer and cookery teacher based in South London. And her mission is to share just how simple, nourishing, and delicious Japanese food can be. She has been featured in many prominent publications, as well as being consulted widely as an expert on Japanese cuisine.

I first met Yuki at her lovely home in South London about 10 years ago, and I remember it well as I was expecting my first son, and I was so hungry and the food tasted so delicious! So I’ve continued to follow Yuki avidly because I find her way of simplifying Japanese food very empowering. You can do certain small actions at home, which you had no idea about…

For example, recently she’s empowered me to make some kinako, which is a flour made from dried and roasted soya beans. It’s very simple. I didn’t know I could make it, and I love it on Greek yogurt! So thank you very much for the inspiration. A huge welcome to you Yuki. Thank you so much for joining me.

Yuki: Hello. Yes, I’m Yuki! So thank you for having me, and I’d love to talk about my passion today!

Vanessa: Excellent. I can’t wait. So, we can’t talk about Japanese cooking without talking about soya beans: they’re everywhere. Yeah. And it’s amazing where they are!

I was really amused when you told me that one of your Japanese friends actually hadn’t realised that edamame and natto were made from. So in fact, they are soy at different stages of their life, right?

Yuki: Exactly. I mean, edamame is just a fresh one and boiled. So just keep the… stay nice, beautiful green colour, and it’s just lovely to have the snack. You can buy from the frozen, everywhere in supermarket now. And, yes, we call daizu which is normally used for making for kinako, or natto, and stuff. So that’s a dried soya bean. So, that we call daizu. So it’s quite different part. You can buy dried soybeans from health shop, and you can make homemade miso and stuff. So it’s really…and kinako you said, you mentioned earlier.

Vanessa: What are the main Japanese foods made from soybeans?

Yuki: Miso, natto, do you know natto? (laughs) and, yes, soy sauce obviously. So that’s the main staple seasoning: Japanese. Yeah, soy sauce, everybody even has it in England now. And miso, that’s the real core Japanese ingredient and yeah, like flavour. Japanese flavour.

Vanessa: Excellent. So, I think there’s just so much soy in Japanese food. And could you put people’s minds at rest who might be worried that eating too much soya might not be good for you? Maybe they’ve read something and it’s stuck in their minds…

Yuki: Yes. This, that’s bit like… soy product can be a little like controversial, but it’s still… a lot… I research a lot, but still not that answer yet. But my experience, I grew up in Japan. I grew up with soya product, every single day every from, you know, since child. And then one of the facts is a lot of Japanese ladies has got less breast cancer result and much healthier. And also menopause problem much less compared to Western cultures… people. So that’s reason because we have a lot of soya diets.

But on the other hand, Western diets, you know, a lot of like breast cancer case, they shouldn’t eat because of the oestrogen. So affects women’s hormones, so we don’t know which one to believe, but as on the Japanese side, I’m very healthy. My family’s healthy, and a lot of Japanese people, much less breast cancer. But I found is that GMO basically genetically modified…that’s the cause of the huge problem.

So I would say, I stick with, as long as organic and no GM soya beans, so then should be fine. And then also everything is in moderation, isn’t it? So you shouldn’t eat like soya beans every day for like tofu, tofu, tofu or natto, all the time.

Vanessa: I’m sure because they come in so many different ways. You don’t need to eat the same thing. Like the different processes have different effects.

Yuki: Exactly. And then especially Japanese diet eats so many… eat everything… so little.

But we don’t eat like whole block of tofu per person or anything. It’s just like always things, small amount and balanced diet. So I would say like, yeah, as long as moderations every day…

Vanessa: A wide variety of foods. Yeah.

Yuki: And a good quality. That’s the key I think. Yeah.

Vanessa: Okay. So I’ve been really interested in your miso and koji making workshops and I really want to join it, and I just realised how magical koji is! I didn’t know anything about it, I didn’t realise… so could you tell us about that?

Yuki: Yes, koji is starting… people starting curious about, and then starting kind of one of the ‘trendy’ fermentations. So koji is a mould, so Japanese national, like Asian, um, mould! (laughs)

So it’s very… it sounds like: mould??? Everybody’s like: what?

Vanessa: Sounds delicious! (laughs)

Yuki: Actually mould isn’t always a bad thing, some cultures like French using for the cheese making. So each culture has got different, uh, type of mould and millions different type of mould. Anyway, so the specific mould called koji. So that’s very important for Japanese cuisine and Japanese culture. Uh, so basically all the most important or staple Japanese food has got koji in it.

Yuki: For example, like making a miso, and soy sauce, mirin, rice vinegar, and sake, it’s anything like fermentation and a staple Japanese seasoning or ingredients, uses the Koji.

Vanessa: Anything that’s fermented, the magic ingredient is koji and… where can we get koji? How do we get our hands on it?

Yuki: Yes. Koji mould itself… to be honest… spores… you shouldn’t, I mean, you can’t get, you can’t grow yourself. So we have a koji shop… it’s like very like, heritage. So keep the koji mould. Then actually make koji rice.

Basically – mould – you need to grow somewhere, right? So that means, so you need to feed on the grains then making, basically, koji rice, or koji wheat, or making a koji product. Make sense?

For example, when you make the sake, you need to, koji grow on the rice, to brew the sake. So, that’s, that’s how you keep it. And koji rice, or koji wheat, or koji product you can get from the supermarket. Or you can get from even Amazon UK.

Vanessa: Oh, wow. So you are doing workshops using koji as well?

Yuki: Yeah, Koji rice basically already grow on the rice, so that’s makes with the… cook with  the… fermented with the cooked soybeans.

Vanessa: Yeah, that sounds really interesting. I saw, I was really interested to see you can make, um, almost like dressings like ‘lemon koji’ and you can use it in place of salt, is that right?

Yuki: Exactly. So basically, koji for example, like… contains a variety of enzymes, so then breaks down, so that makes fermentations, which is improved, amino acid. So it itself, is  umami, basically…

Vanessa: Ah, yes!

Yuki: So that’s why taste umami is like a fifth taste. So basically umami means yummy taste!

Vanessa: Yummy taste… koji equals yummy taste.

Yuki: Yes. So that’s why I do a lot of koji product, basically, shio koji or double fermented soy sauce. So it is koji, and then I pour the soy sauce to ferment it about 10 days. And, uh, basically double fermented, soy sauce, basically.

Vanessa: Oh wow.

Yuki: Like full of flavours and full over nutrition like, vitamin, minerals and yeah. So it’s amazing product. It’s very hard to explain and introduce to Western culture.

When they come to my workshop and people taste it, it’s just simply like: Oh my gosh! It’s so yummy!

Vanessa: Oh yeah. I’m really interested. I think I have tended to use quite average Japanese ingredients and I’m realising it will be so much more delicious if I, you know, use more of a craft ingredient.

Yuki: Yes. Yeah, I mean miso, soy sauce itself is already koji in it and then fermented, so it’s already a lot of flavours, which is, umami based food. But again, I try to do more umami koji product.

I just boost more, so that means more extra umami, more nutrition values. It’s just amazing for the gut health. Uh, we can talk about later more, but incredible health benefit and also tastes so much better.

Vanessa: Ah, amazing. So how can we use miso? Because I just discovered, I mean, I do find it difficult to have a lot of time to cook, but I know it’s so easy, but I just discovered some at the back of my fridge and I thought, why haven’t I used this miso? And I think maybe I’m a little bit limited in how I’m using it!

Could you give us some more tips about where we can throw miso in?

Yuki: Definitely! Yes. The miso. Yes. Miso is yes. A lot of people exactly the same answer. Like: oh, I have a miso! But I kept it in, in a fridge for like a year now, so it’s still okay to use? So a lot of people ask…

So miso is associated obviously with miso soup, but it’s not only miso soup. Miso soup is just one of the dish. So miso is core Japanese ingredients, I mean seasoning to use lots of different dish.

For example, you can make dressing. So like a little bit of vinegar, and miso, and mirin, and um, maybe honey, making like a little vinaigrette, a miso dressing.

Or if you want, because such a power of the umami in miso. So if you wanna lift up the flavour, so sometimes if you make, let’s say, like a tomato sauce, or pasta sauce, or bolognaise sauce or something, then it’s sometime taste it, and then something is missing. You know, something?

And a lot of people end up putting a lot of salt. And then gets salty. And then ooh, it’s a bit too salty. So, because that sauce has a lack of umami flavour. So you, if you dropped a little bit of, um, you know, tablespoon or teaspoon even, of miso then it certainly lift up this flavour.

Vanessa: That’s brilliant. I’m gonna try that because I keep… I end up putting lots of Worcestershire sauce in things. Which is nice. But my husband, he’s from Peru, and he didn’t grow up with Worcestershire sauce, so he doesn’t really like it as much as I do. But he loves Japanese food. He lived in Japan for eleven years.

Yuki: Vanessa, you’re using the umami technique! Worcestershire sauce is full of like ferment, I always said, English soy sauce.

Yeah. People naturally put it on some, you know, like seasoning to more improve the flavour because they are fermented, they are full of umami. Just exactly the same technique.

Vanessa: Yeah. Oh, that’s great. I’m gonna mix it up a bit. Yeah!

Let’s just move on to a little bit more about the health benefits. So you mentioned that you got ill a couple years ago, and I understand that you’ve addressed this with changes to your diet. Could you tell us a little bit about that; what changes you made, how it benefitted you?

Yuki: Yeah, I love to share about my experience. That was so amazing. I had a great experience. Obviously like, shocked about… just become the pandemic start, and obviously my working slows down, and I felt something weird. And then I thought I was working too much, but I found out basically I had an autoimmune disease, which is rheumatoid arthritis.

So basically this is a part of the autoimmune disease. So, which is a lot of people might have and suffer from. Yes, I tried to find out, I was really shocked myself and I dunno what to do with it and obviously talk to doctor about it and a lot of medications, options… So then I decided, I talked to my husband to help a lot to improve. So I decided to: right, something going on to my body and I need to change my life. I should find out what’s going on with my body, actually. So I just a lot of research and test, test, test myself and what’s going on…

So, and I found out a lot of related with gut health. And a lot of people, yeah. So basically I have to improve my gut health and it is millions books I read, article about it, and I think it’s really important to fix my gut or find out. Then reading book information is finding answer has become more like a Japanese food and a Japanese diet. And then fermentation is so powerful. So now I starting into a lot of testing a lot of crazy diet and then…

Vanessa: Wow. Yeah.

Yuki: I’ve been doing like gluten free diet, and I have my intolerance, food intolerance test. And that’s very important to understand yourself and, uh, yes… end up at koji, fermentation. Japanese food is… think about Japanese food: it’s, uh, soy sauce, miso, sake, rice vinegar – everything is fermented.

And, uh, I just naturally back to my original diet, which is Japanese, traditional Japanese diet.

Vanessa: Yes. So, mm. I’ve been reading a lot about gut health. It’s interesting ‘cause it’s kind of… in the way that koji is the origin of umami, is like the gut is the origin of health in, in many ways, in many senses, isn’t it?

Yuki: So I’ve been doing, so I started more, um, like fermentation diet, using more koji product for my… anything! Like it’s not: only eat Japanese food, it’s not like this.

For example, I’m making, uh, guacamole, which is avocado. I love avocado. And, I just put in lemon koji, which is: I fermented the lemon with the koji, and instead of using just the lemon juice, using the lemon juice and salt, I’m just using the lemon koji, which has salt in it. Yes. So I just put in one tablespoon of lemon koji, fermented lemon koji and crush the avocado.

So it’s not only traditional Japanese food, but using the Japanese method or technique to improve my gut health and it’s basically cure my disease. In six months it’s back to normal, normal results.

Vanessa: Oh, wonderful. I’m so glad that you’re feeling better.

Yuki: Yeah, I’m so, I’m so glad, that’s why I just wanted to share my experience, as well.

Vanessa: Yeah. I think there’s a lot to learn from that. I definitely need to come to your workshop. I need to get some koji in my life.

So, the ingredients in Japanese cooking are so important, as we’ve been talking about. And could you tell us some of your suppliers, which are your favourites? For example, where can we get this koji in London?

Yuki: Koji in London… You can buy – actually, you can get it local. I like to try to use local products as possible. And one of them: Kanpai, which you can get from, is a sake brewer in Peckham, South London. They have, obviously, they basically produce the sake, so they have their own koji, rice koji.

Vanessa: So it’s like the by-product of the sake making process. It’s the rice that’s been processed.

Yuki: Yeah. So they have that koji obviously, and obviously, of course you can buy from Amazon.

Vanessa: Okay. I wouldn’t have, I wouldn’t have even known, but you can get everything!

Yuki: Yes. Everything, it’s crazy! And also, koji itself and also soy sauce. Japanese cooking’s so simple. So I normally said five core ingredients, which is, in terms of the seasoning: miso, sake, mirin, soy sauce, rice vinegar, so there is koji in it anyway. So these products, pretty much cover most Japanese recipes.

So that means you have to have good products, makes your dishes much tastier. So I normally suggest a good product, which is – Clearspring is amazing. They are pretty much, most product, organically made, and also the Wasabi company. They are very, obviously they suggest, they grow their own fresh wasabi.

Vanessa: That’s in Sussex, isn’t it?

Yuki: Yes… That’s in Dorset. In Dorset they grow the fresh wasabi and also they sell in online shop, sell the amazing Japanese products, like really high end products, I think. Um, that’s kind of a place I normally choose.

Vanessa: I really think I need to up my game now! I’m inspired and I’ve just been thinking about things for the kitchen. I was just admiring your sushi tea towels on your website. They’re absolutely gorgeous. And could you tell us one Japanese kitchen item that you couldn’t do without?

Yuki: Without… just think… the Japanese… obviously Japanese knife is incredibly amazing. I have to have, I love knives. It’s very sharp and beautifully made. It’s nice. It’s a pleasure to cook actually.

Vanessa: Yeah. Do you let your daughter use the sharp knives? How does that work? I’m really interested in getting the kids involved, but I want to use a proper knife.

Yuki: Yes, of course I’m not giving her a, like, long sushi knife so it’s not yet, but, kids, they have… there are some kids knives as well, a bit more safe and has got a little bit more protected.

So, which is started slowly, introduced, but actually kids are very capable to use. So as long as teach how to use it, for example, try to hiding the other side of the fingers.

And how to hold a knife and slowly, slowly, I teach her (suprised she listens to me!) and then they using slowly to, you know, like start using the knife. So, um, obviously it can’t start with a big knife. Starts with a kids’ knife, just like a little smaller one and slowly, slowly introduce proper knife.

I think kids are amazing to adapt, you know, quickly.

Vanessa: Yes. They, they’re sponges aren’t they?

And could you tell me what your favourite Japanese word or phrase or saying is?

Yuki: Oh yes. I love the: 一期一会 ‘Ichigo, Ichie’ the word is basically, each moment is always a once in a life experience. So this, yeah, I like to, every moment, every time meet someone or new person or friend, old friend, or I like to do, more value to it at the time. So that’s the meaning. It’s very important. So share the time, share the moment and always don’t waste.

Vanessa: Yes. I love that. It’s really beautiful because yeah… We need, this is, you know, this ethos of eating well as well. It’s like to savour the moment. It’s beautiful.

Yuki: Yeah. That’s, you know, I met Vanessa 10 years ago, but still the moment you remember, I remember you’re here, then after years… but still we can collaborate something, or talk about koji now!

Vanessa: Who knew? (laughs)

Yuki: Yeah. Amazing moment. I like to be I think it’s very important things in their life.

Vanessa: Yes. So just could you tell us one quick action?

So I, when I looked at your website, it’s really interesting, your newsletters are great, so people should sign up for your newsletters because they’re really practical.

And I love the way – I talked about kinako – feeling empowered to make that, but also I noticed, you’ve got a recipe for shichimi togarashi on your website… things that people didn’t even know that they could make. You know, just buy a small packet…

And so could you just tell us one other quick action that we could take to bring healthy Japanese eating into our homes every day?

Yuki: Yes. I think it’s a lot of people, in their heads, everything’s from scratch is like too much, oh my, I don’t have time, but actually, it’s just… you don’t need to do like too much, just simply… but from the scratch is very important.

So little things make a huge difference. For example, I do little, I dunno, a lot of people just go to the premade food from a supermarket. But just simply grill the fish, and simply cook the rice, and that’s it.

Or making a stock. But Japanese stock, I did it, in the cafetiere to make the stock.

Vanessa: So how do you do that?

Yuki: It’s really, it’s bizarre, but actually it works very well. We call bonito flake stock, which is a fish stock. So the dry product, actually Japanese food, a lot of it based, and other things, umami, which is a dry product. So bonito is a fish flake, like dry dried bonito, right? Bonito Flake. Just a hand full, chuck into that, do you know, cafetiere, coffee maker?

And just exactly the same, so pour hot water, boiling water. Leave for about two, three minutes, just brew like a coffee or tea. And then press, and you’ve freshly made the fish stock. It’s ready!

Vanessa: Brilliant. Katsuobushi, isn’t it?

Yuki: That’s it.

Vanessa: So, oh, that’s great because I do, I’ve got dashi in the cupboard as well, the powder, and I sometimes think, mmm, what’s in this? I don’t really know what! You know, my kids like it, they love Japanese flavours. So I put a little bit in when I’m making some noodles, but it would be so nice to just make it in the cafetiere and then I know what’s in it. Exactly what’s in it.

Yuki: It’s instant, isn’t it? But it’s a real fresh one. So I try to not to use chemical instant powder or pre-made thing. People in their head is: oh, this is easy. That’s easy. Instant. But a lot of things you can make from the fresh. Fresh, but like, instantly.

Vanessa: Fresh but instant. Yes!

Yuki: Yes. Fresh. Fresh instant. So yeah, that’s kind of my idea. And encourage people it’s more healthy, fresh food every day.

Vanessa: Wonderful. Oh, that’s been so interesting. So I’m aware of the time. I’ll start to wrap up. If you could just let us know where we can best find you.

So your newsletter’s great. People can sign up on your website. What’s your website?

Yuki: Website: And you can find a blog. A lot of my workshop dates and schedules you can find at my website.

And also, I do Instagram. I quite like to share my life, you know, what am I making, what am I my eating, sometimes my daughter appears. So yes, I do a lot of sharing that little tips, cooking tips, stuff. So I’ll do a lot of that Instagram, so it’ll be great to share my Instagram.

Vanessa: And what’s your Instagram handle?

Yuki: @yukiskitchen. It’s kind of pink ‘YK’ logo.

Vanessa: Yeah. Got it. Okay. Well thank you so much. I really, really enjoyed our conversation.

Yuki: Thank you so much too. Yes!

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Thank you so much for listening!

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