From fresh vegetables to fermented food

Once we’ve grown and harvested crops we can use other microbes to unlock flavours and energy locked up chemically in food. This is the process of fermentation. And here to give us a digestible account of how it works is Cambridge University chemist, Ljiljana Fruk. And she brought Chris Smith some cabbage...

Ljiljana -  I actually did and I did this experiment myself. So we are going to test it and this is a sauerkraut made by Ljiljana. This is the starting reagent.

Chris -   Okay, so sauerkraut is made from cabbage seed, you’re offering me a jar jammed with raw cabbage. I’ll just grab some of that.

Ljiljana - Yes it is.

Chris - You want me to eat this?

Ljiljana - Yeah I want you to try this.

Chris - I quite like cabbage actually. That’s quite nice, actually.

Ljiljana - Yeah but it doesn't taste like much doesn't it? But if I offer you now a fermented cabbage, which we know as a sauerkraut? Tell me if you would like that a little bit more.

Chris - Okay. So what Ljiljana is now giving me is a plastic pot. You can still recognise this as cabbage in here but it's almost translucent. So here we go.

Ljiljana - Yeah. And it's softer. I think you would feel. I think you would admit it has a little bit more flavor.

Chris - It has a lot more flavor. It's a sort of vinegary texture. So a little bit of that and it's much more acid.

Ljiljana - Yes.

Chris - And it's much softer.

Ljiljana - Yes.

Chris - So I can almost melt away the cabbage with my tongue just rubbing it against the roof of my mouth, rather than having to physically masticate it with lots of jaw action

Ljiljana - Absolutely.

Chris - Now you're calling it fermented cabbage. You haven't done anything apart from let microbes do that I presume. This is the work of microorganisms.

Ljiljana - Exactly, some microorganisms which are living in the leaves of this cabbage are actually there and they have done this process. You just have to treat this cabbage with a little bit of salt, so you have to put salt in water, and you have to keep this cabbage in an airtight container. And these microbes which are present on the leaves will make this chemical reaction go faster and produce then, a range of chemicals and products which are not originally present in the cabbage,

Chris - So critically it's the conditions in which you keep the material once you have chopped it up and prepared it. So the lack of air. You've excluded oxygen. And the salt, what does that do? Select for the right sorts of bugs. So the raw cabbage is going to be covered in a whole population of microbes isn’t it?

Ljiljana - Yes, exactly. And in general, you know, the microbes will be in air that will be on our skin so they’re in the plants as well.

So by adding the salt you are selecting for good bacteria that will do some of the fermenting reactions and they will produce acid as a product. And this acid will then select for another type of bacteria which is again good, which will then induce a flavor enhancement of this food. So what is interesting about this is that despite these bacteria being the same in Croatia or in Britain, they will still have a slightly different product just because the cabbage will be a little bit different because it's grown differently. And I think this is the beauty of fermentation particularly for food preservation or for enhancing the quality of food, that you can have the same types of microbes maybe in a little bit of a different ratio and they will give you a slightly different product.

Chris - It's the bacteria liberating various chemicals that they have the biochemical knowhow written into their genes to release, from the food.

Ljiljana - Exactly.

Chris - But you are forcing the direction they take because you make the conditions ideal for just some of them. Because I wanted to touch on the difference between food spoilage and fermentation because if I took that same cabbage with those same colonies of microbes and I just left it on the table, or in the same pot but not under the conditions you put it in.It wouldn't be half as appetising.

Ljiljana - Yes and you probably had that already so you would have this, kind of, gooey black mass which will be formed and this is because you are now having different conditions which will select for negative bacteria, for these bad bacteria that will cause the rotting. So it's a thin line between the fermentation, between the good and the bad. And it's always about the ratio. And the interesting thing is that we have also in our gut the same types of bacteria, similar types. Some of them are good, some of them are bad so it's very important to keep this balance
Chris - You know a little bird told me, Ljiljana, that you're actually going to open a restaurant which is informed by this technology.

Ljiljana - Yes. And we are unfortunately not the first one so there is a restaurant in Copenhagen called Noma, a famous restaurant that started working on fermentations. And so a friend of mine is a chef and we realised that fermentations are extremely important for unlocking the flavours. So we are going to study some original wild organisms, microorganisms and see how they're affecting the food in geographic context. How is the food in Southern Europe different from the Northern Europe? And it will depend on the fermentation conditions.

Chris - Where’s the restaurant?

Ljiljana - In Zagreb. So it's opening in a month.

Chris - Oh no! I love Zagreb. It's a beautiful city. I was there a year or so.

Ljiljana - So you will get an invite but you need to do some work in our fermentation lab as well. So you might have your own strain of microorganisms. The Naked Scientists strain

Chris - And apart from cabbage what else are you going to ferment.

Ljiljana - So we will do vinegars as well, we will do all kinds of sauces and you can basically ferment any kind of vegetables and foods which can be found in that part of Europe.