Ever sipped on a sweet daiginjo sake and pictured bananas, or the mellow sweetness of melons? And yet, while you're picturing orchards or tropical fruit baskets, let's just be clear that nope, no fruits are present. Sakes are not made with anything other than rice, water and yeast. In fact, there's a strict no-additive rule in the world of sake.

So, where do these lush, fruity flavours come from?

At the heart of it is a splash of chemistry. All sakes dancing around with no more than 10 basic aromatic components. It's true. The distinct character of each brew? That's just a game of mixing and matching these components in different proportions.

But your culture and upbringing plays a part too. If you've ever met someone who can't stand the smell of a certain foods you adore (looking at you, durian lovers and haters), you'll know there's more to aroma than meets the nose. Something that smells divine to someone in Malaysia might get wrinkled noses in Europe and maybe even induces gagging. It's all down to personal experiences and the food we've grown up with. Our perception of flavours and aromas are influenced by our past and what our parents fed us after all.

The key to flavour in Sake

Rice is often the headliner when chatting about sake. And rightly so. Yamada Nishiki rice is known to impart more fruity and floral notes or while Omachi more robust, earthy vibes. But the best kept secret of most of the sake industry is really yeast.

Yeast, the unsung hero of the sake world, wields more power over the flavour than most realise. Even if you start with a single type of rice, using different yeast strains during fermentation can whip up a broad spectrum of sake flavours and aromas. Yeast is the magic powder that gives you the light, airy floral tones, and the deep, resonating earthiness of sake.

Over the last century, the Japanese sake industry really got scientific about yeast; researching, cultivating, and designing specific yeast strains to brew sake. As the years rolled on, more yeast strains popped onto the list. Modern brewers now had a tool kit, letting them zoom in and achieve very specific flavour profiles. This explains why most sake brewers now use cultured yeasts, all primed and ready for action in a tailor-made environment. The Brewing Society of Japan keeps tabs on this, diligently recording every tweak and test through the years.

While sake brewers in the past had to contend with the unpredictability of microbes and yeast in the air, brewers today who use cultured yeast can sleep easy, knowing that the pesky undesirable microbes won't crash the party. And with a huge catalogue of yeast strains available to brewers, the concept of "designing" sake's flavour has taken off. It's a bit like shopping for the perfect outfit; brewers can now pick and choose the ideal yeasts to craft the aromatic profile they fancy.

With the market clamouring for fruity sakes, researchers have created a number of new yeast strains to cater to this demand. Some of these new-kids-on-the-block come from places you wouldn't expect, like flowers. Amabuki Shuzo, for instance, developed yeast strains derived from flowers. It's a testament to the lengths the industry will go to appeal to the consumers.

The chemistry of a fruity sake

If you’ve tasted a good ginjo or daiginjo sake, you'll be familiar with that clean, fruity aroma of bananas, melons and pineapples. This signature scent has a name; the Japanese dub it “ginjo-ka”. Behind the ginjo-ka is lesson in chemistry.

Modern daiginjo sakes owe their fruitiness to two main flavour compounds: isoamyl acetate and ethyl caproate. As mentioned above, sakes dancing around the same basic aromatic components. It is the ratio and proportions of these two compounds that determine whether you're getting a vibe of a tropical fruit party or subtle white florals.

Up till the early 2000s, many ginjo and daiginjo sakes contained a large amount of isoamyl acetate. They had a very fruity nose with prominent aromas of bananas and honeydew melon, with a clean palate.

But consumer tastes evolve. The public's palate craved for an even fruitier sake and a heavier ginjo-ka. The researchers obliged, working tirelessly to breed new yeast strains that raise the levels of ethyl caproate. This compound makes sake even more expressive, bursting with ripe apples, pears and pineapples.

Still, brewing sake isn't just throwing things together and hoping for the best. It's a meticulous art. The brewmaster walks a tightrope and maintains the balance of every key compound. For example, while isoamyl acetate is great for that banana aroma, go overboard with it and you risk your sake smelling like industrial solvent and nail polish remover (you might have encountered sakes or whiskies that smell like both bananas and nail polish). Similarly, an excess of ethyl caproate, can cause the drink to swing from delicious apple and pear notes to musky, mouldy cheese, gamey mutton or a barnyard with a lot of animals.

As we mentioned earlier, drinkers from different cultures might have vastly different perceptions of the same sake. This is why some savvy breweries have been tweaking their sake recipes to please their overseas customers. They've upped the ethyl caproate levels, betting on international drinkers' love for fruity aromas, even if there's a hint of muskiness that the Japanese palate couldn’t accept.

The wild side of sake fermentation

We’ve just discussed how the magic of using cultivated yeast. However, some brewers shake things up and toss this modern playbook out.

Instead of cultured yeast, they're taking a walk on the wild side, embracing the untamed strains floating around in their breweries. Yep, we're talking walls, machinery, the lot! And it's this dance with unpredictability that makes things truly captivating.

Welcome to the world of natural fermentation or, as the Japanese call it, “shizen-jikomi.” It's all about reducing human intervention (cultured yeast) and harnessing the power of the wild yeast present in the environment. Now, it's not all sunshine and rainbows; there's a good chunk of risk involved. But, when the stars align, these wild yeast strains can churn out some seriously standout sakes. For anyone tired of the same old 'clean' sake taste, these wild brews might be your ticket to a flavour adventure.

Some brewers ‘cheat’ a little. Once that wild party, or the starter, they may sneak in a bit of cultivated yeast to guide the process. Think of it as adding a bit of structure to the spontaneity. This ensures that the fermentation doesn't go too off-piste and keeps a certain flavour profile in check.

But let's get real- brewing with wild yeast is not a walk in the park. This method is unpredictable and the results are harder to control. The untested wild yeast has to survive dramatic temperature swings that each sake batch undergoes, and it must be robust enough to chomp down on high sugar levels without getting overwhelmed.

Given the challenges and uncertain payback, it's no surprise that only a handful of breweries today dare to walk this wild path. But those who do, like Tamagawa Sake from Kinoshita Brewery in northern Kyoto, are really onto something. Their brand is an excellent example of wild yeast's potential. They are headed by the first-ever non-Japanese toji, Philip Harper from Oxford, UK, who seems to have found the secret sauce in using wild yeast. The result is sakes with intriguing aromas, intricate flavours, and an impressive alcohol kick. Their house yeast doesn't mess about, consistently delivering sakes with a whopping 20-23% ABV.

The chemistry of an aged sake

Sakes of the clean and delicate sort are generally best enjoyed fresh out of the brewery. But many sakes are also deliberately aged by the brewer, transformed over time to acquire a very complex character. They are known as “Koshu” in Japan.

Ageing helps to round off the rough edges, add a caramel richness, honeyed sweetness, nutty undertones, and sometimes even aromas reminiscent of a fine sherry. Most sake are kept in the cellar for a few months to years. But for sake varieties with greater acidity and amino acid content, their ageing period can stretch much, much longer.

As the sake sits and contemplates life in the cellar, chemical reactions continue inside the bottle. The Maillard reaction (the same reaction that browns your morning toast and porterhouse steak) brings out those hints of caramel, adding a nutty zing, and even sliding in a touch of soy sauce. Amino acids also interact with alcohols, forming various esters. These esters can lead the flavour profile anywhere from the familiar fruity arena with our pals Ethyl Caproate and Isoamyl Acetate, to the buttery note of Ethyl Lactate.

Moderate oxidation also creates various aldehydes, like Isovaleraldehyde from Isoamyl alcohol. This particular aldehyde is responsible for adding most of the nutty notes to long-aged sake.

When sake aromas go wrong (or bad)

By now, it’s clear that making sake is super complex. Just as the right techniques can create a beautiful drink, a minor slip-up could lead the flavours off-track. Be it fermentation imbalances, surprise contaminations, or just a bad brewing day, these blips can result in a variety of smells that no one would enjoy.

A notorious culprit is 2 4 6-Trichloroanisole (TCA), which sounds like a biochemical weapon but is essentially an unpleasant mouldy and musty odour. It is a menace to not just sakes, but also wines and other drinks. This is known as "cork taint" in the wine industry.

Because TCA is so pungent, even a very small quantity of it won’t go unnoticed by a casual drinker. Caused by chloride-treated wood, its potency is so strong that it doesn't just taint the sake it comes in contact with but can even affect bottled sakes nearby as well. Dealing with TCA could be a nightmare – more often than not, it involves saying goodbye to all contaminated wooden equipment.

A excess of amino acids during fermentation could cause a sulfur issue in sakes. This causes a whiff of rotten eggs or burnt rubber in your sake thanks to hydrogen sulfide (H2S) and other sulphur compounds.

Lactic acid levels have to be managed well too. A wee bit of this yogurt-like aroma could add complexity in more robust sakes, but too much of it in a delicate daiginjo would ruin the melody.

Storing Sake Right

Finally, let’s not forget that sakes don’t keep for long. Improper storage would make your sake go bad too! While wine’s arch-nemesis is oxidation, sakes deteriorate when its aromas dissipate. Particularly for ginjo and daiginjo varieties with tons of ethyl caproate fruitiness, the dissipation of ethyl alcohol can leave behind pungent caproic acid, which turns your refined sake experience into a goat cheese fiasco!

So here’s the golden rule: once you pop that sake bottle, treat it like an opened bag of crisps. Dive in and enjoy before the essence fades. If you’re keeping it for later, make sure to keep it in a refrigerated environment and finish it within a week or two week tops. Otherwise, that expensive bottle of daiginjo won’t quite taste the same again.

@CharsiuCharlie