What is Fermentation? The Living Process Behind Oichi Kombucha

Fermentation can sound complicated, but at its heart it is something beautifully simple: microorganisms transforming ingredients into something new. It’s one of the oldest ways humans have made food and drink, used for thousands of years to create everything from bread, yoghurt and cheese to wine, kimchi, vinegar — and, of course, kombucha.

At Oichi, fermentation is at the heart of everything we do. We don't simply add flavour to tea to make kombucha. We give tea, sugar and a living culture time to work together, allowing yeast and bacteria to naturally transform the brew. That transformation is what creates the acidity, complexity, depth and distinctive flavour that makes Oichi kombucha so different from an ordinary soft drink.

So, what actually is fermentation?

Fermentation happens when microorganisms such as yeast and bacteria consume sugars and use them as a source of energy. As they do this, they produce other compounds including organic acids, carbon dioxide and a huge variety of flavour and aroma compounds.

In other words, fermentation isn't simply one chemical reaction. It's a living, evolving ecosystem, and that's particularly true of kombucha.

How does kombucha fermentation work?

Traditional kombucha begins with surprisingly few ingredients: tea, water, sugar and a living kombucha culture. The culture is often referred to as a SCOBY, which stands for Symbiotic Culture of Bacteria and Yeast.

The sugar isn't simply there to make the drink sweet. It provides food for the microorganisms within the culture. During fermentation, yeasts begin breaking down sugars and producing small amounts of alcohol and carbon dioxide. Bacteria then work alongside them, converting compounds including alcohol into organic acids.

As the fermentation develops, the original sweet tea gradually becomes brighter, more acidic and increasingly complex. This interaction between yeast, bacteria, tea, sugar, oxygen, temperature and crucially time is what creates kombucha.

Why we ferment slowly at Oichi

Fermentation can't be rushed without changing the result. At Oichi, we use traditional methods and allow our kombucha to ferment slowly in small batches because flavour develops over time.

In the earlier stages of fermentation, you may notice more sweetness and delicate tea flavours. As the culture continues working, acidity increases and entirely new aromas and flavours begin to emerge. There is a point where sweetness, acidity, tea and fermentation come beautifully into balance, and finding that point is part science and part craft.

It's one of the reasons we don't believe kombucha should simply be manufactured to a formula as quickly as possible. We brew it, we taste it and we give it time.

 Quality tea matters.

Tea isn't simply a backdrop for Oichi kombucha. It brings tannins, polyphenols, flavour and structure to the finished drink, while also providing important compounds for the culture itself. Different teas can produce remarkably different kombuchas.

At Oichi, our Original Kombucha begins with Sencha green tea, for example. Its fresh, delicate character becomes the foundation upon which fermentation builds acidity and complexity. This is one of the fascinating things about fermentation: you don't completely lose the character of your starting ingredients; you transform them.

The Second Fermentation Process

Once we have created our base kombucha, we begin the second fermentation, where we build another layer of flavour and character. This is when ingredients such as ginger, turmeric, mint, hibiscus, rose, citrus and seasonal fruits and botanicals come into their own.

Unlike the first fermentation, our second fermentation takes place in the bottle and is much shorter, usually between one and five days, or for as long as each particular brew needs. During this time, the remaining yeasts and bacteria continue to work, naturally building carbonation while the fresh ingredients and botanicals infuse into the kombucha. This creates another dimension of flavour, adding complexity and depth without losing the freshness and character of the fresh ingredients themselves.

Getting this balance right is important. We want enough time for the flavours to develop and become part of the ferment, while still retaining the bright top notes of fresh ingredients such as lemon, ginger and turmeric and the delicate aromas of botanicals such as hibiscus, mint and rosemary. As with our first fermentation, we don't simply rely on a fixed number of days, we taste and allow each batch the time it needs.

Because we love working seasonally, you'll also find us experimenting with ingredients that are available for only a short time each year, such as fresh elderflower. Working in this way allows the seasons, and the ingredients available to us at that particular moment, to become part of the character of our kombucha.

Taste the Flavour of our fermentation process for yourself: Explore our range of live kombuchas, from bright Lemon, Ginger & Turmeric to floral Hibiscus & Rose, each made using our slow fermentation process and real ingredients.

Explore our range of live and naturally fermented kombuchas here.

Why is kombucha naturally low in alcohol?

Alcohol is a natural intermediate part of kombucha fermentation. Yeast produces small amounts of alcohol as it consumes sugar, but the bacteria within the kombucha culture then use much of that alcohol and convert it into organic acids.

This is one of the things that makes kombucha fermentation so interesting. Rather than fermentation being directed towards producing alcohol, as it is with wine or beer, the community of microorganisms continues transforming the brew. The result, when fermentation is carefully managed, is a complex drink that can remain naturally very low in alcohol. Oichi kombucha has less than 0.5 % alcohol.

Fermentation creates flavour

Perhaps the biggest misconception about kombucha is that fermentation is only there for the health side of the drink. For us, fermentation is also about creating flavour. A well-fermented kombucha has acidity, aroma, body and length. It can move across your palate in a way that a straightforward sweetened drink doesn't. Acidity can cut through rich foods, tea provides tannin and structure, botanicals provide aroma, and a small amount of residual sweetness can balance acidity. Fermentation ties all of those elements together.

That's why we love serving kombucha with food and why we think it deserves the same consideration we give to wine, beer or any other carefully crafted drink.

Why we keep our kombucha live

Once fermentation has created a living drink, producers have a choice about what happens next. Some kombuchas are pasteurised or processed to increase stability and shelf life. Oichi isn't.

Our kombucha is live and unpasteurised, which means the living cultures that are part of the fermentation process haven't subsequently been destroyed through pasteurisation. For us, keeping these cultures alive is an important part of making kombucha traditionally and preserving the integrity of the ferment. It also means our kombucha retains the naturally occurring bacteria and yeasts created and nurtured through fermentation, one of the qualities that makes Oichi kombucha so unique.  Kombucha really does have a lot to offer - spectacular health benefits and  layers of flavour not normally found in soft drinks.

Keeping our kombucha live does mean it needs to be treated differently from an ordinary soft drink or mass produced kombucha. It needs to be kept refrigerated, where the cooler temperature slows down the activity of the living cultures and helps keep the kombucha balanced. For us, that extra care is absolutely worth it. We want the kombucha you drink to remain as close as possible to the living ferment we created in the brewery.

An ancient process, still alive today

Humans now understand far more about the microbiology behind fermentation, but the process itself is ancient. Long before we could identify individual yeasts and bacteria, people were using fermentation to transform and preserve food and drink, and we are still working with that same natural process today.

At our Norfolk brewery, every batch begins with tea, sugar and our living culture. We then give it time for the microorganisms to get to work. The sweetness changes, acidity develops and flavours evolve until, slowly, tea becomes kombucha.

That's the magic of fermentation: it's not an ingredient added at the end, but a living process that creates the drink itself.