How to engineer a perfect matcha

Matcha is a global phenomenon. About 1.6 million matchas were sold in the UK this summer, while 2 million videos with the hashtag #matcha were posted on TikTok in the past year.

The Japanese powdered green tea has taken over high-street cafes in the form of lattes, iced drinks, and cakes. It’s been prone to shortages due to its sudden propulsion into the limelight.

Matcha fans seek a deep green colour and smooth flavour with little bitterness. As it turns out, bringing this to life is quite an involved process.

Bring on the whisks

Making matcha involves frothing a few grams of the tea in a ceramic bowl with warm water and a bamboo whisk. It sounds simpler than it is: the mechanical action is the difference between making a matcha and simply pouring a green tea.

“When you whisk the tea, you make sure first that the entire whisk goes to the very bottom of the bowl, and then, you whisk it very fast. The movement is all in the wrist, and it's not in a circular motion, but up and down. Then you slow down, and whisk the top surface,” says Dr. Voltaire Cang, a senior researcher of culture at RINRI Institute of Ethics and a tea master in Japan. He’s made over a thousand matchas in tea ceremonies in his lifetime.

When Dr. Cang serves guests at a tea ceremony, he’s looking to make matcha with little foam. During whisking, a liquid film forms to cover the air, creating tiny bubbles. These bubbles move toward the edge of the matcha bowl and sometimes break. Whisking the surface of the matcha then removes the bigger bubbles, creating a glossy surface with a slight microfoam. “You need to disturb the liquid surface as much as possible with waves and random motion,” says Dr Yutaku Kita, a lecturer of engineering specialising in interfacial phenomena at King’s College London.   

Temperature is also key. Over the centuries, matcha-makers have settled on around 80 to 90°C as the optimal temperature. Boiling, or very hot, water is out of the question, as it would cause the foam to disappear. This is because increasing the temperature lowers the surface tension of water, which reduces its viscosity. “If the matcha has a higher viscosity, then it'll be more difficult to break the bubbles,” explains Kita.

The chemistry of matcha

The way matcha is grown and processed impacts the tea’s flavour and texture.   

Tea bushes used to make matcha are shaded (covered) for about three weeks before they are harvested. With the sunlight blocked, the leaves start to overproduce chlorophyll, turning a deep green colour. The plant also makes more polyphenols, which promote foaming through intermolecular bonds and interactions, and amino acids, which stabilise the foam.  The tea’s seasonality and the altitude where they’re grown can make these chemicals more potent in a matcha.  

Even if a matcha isn’t shaded, it can still be possible to produce a light foam under certain conditions. It’s arguably why matcha lattes are so popular. “Milk proteins can improve foaming, as [they] are known to foam very well, and they help stabilise the bubbles, ” says Anniina Salonen, a professor at ESPCI Paris. Given the recent matcha shortages, this means those making matcha lattes could try lower ‘grades’ without affecting the quality of the foam.

Large-scale matcha manufacturing

Back in Japan, matcha producers look after how the tea leaves are processed. After the tea has been plucked, it is steamed to prevent oxidation, which causes the leaves to brown. The heat from the steam keeps the matcha a bright green colour and ensures that the leaves retain their amino acid profile. Then the tea leaves are dried in an oven, and the stems removed. After the dried tea is cut, it’s known as tencha.

Tencha is kept in cold rooms until it is ground into matcha by stone mills. Controlling the mills’ speed is essential in retaining matcha’s colour and taste. This is because the stone mills can heat up the leaves, which can cause them to yellow, like an overcooked vegetable. The faster the mills grind, the hotter the leaves get, causing chemical changes that create a more bitter taste. Luckily, the resulting matcha powder’s fineness doesn’t affect its ability to foam. Because the restricted output of the stone mills can’t always meet demand, matcha’s prices have become volatile. 

Exposing matcha to air causes it to oxidise, so it’s often packed under nitrogen to extend its shelf-life. The tea’s catechins, a type of polyphenol, will brown, so how the tea is stored is as important as how it’s manufactured. Exposure to light and heat can accelerate discolouration, which is why manufacturers often mask green tea drinks in dark or opaque bottles.               

After matcha has been produced, the way it’s served can also potentially change its character. Whether you take your matcha in a bowl or in a glass, Salonen explains that a vessel’s properties can potentially change the foaming capabilities of the liquid inside. “There are some studies on the impact of glass and surface type on beer foam stability, and when it's hydrophobic, it's very bad.”  

There are clearly a lot of factors at play in engineering the perfect matcha.