Matcha is scientifically unstable. 

Matcha is a suspension of microscopic particles, usually with a thick head of froth. Left to time, the particles sink to the bottom and the foam disappears. The rate of decline is determined by the whisking skill and the quality of the tea.

Japanese tea ceremony has a saying: ichi go ichi e. The literal meaning is one moment, one time. The connotation is that this experience, this moment, is unique and can never occur in this exact way again.

It’s a beautiful saying, and conveys a sense of ephemerality – this moment is fleeting… better enjoy it! Same for your matcha!

Why does matcha need to be whisked?

Matcha contains all 3 states of matter: gas (air), liquid (hot water), and solids (microscopic matcha particles). All are important to the sensory experience. All make the preparation more complicated.

Unlike the initial material in coffee, which is extracted and discarded, all the material in matcha is consumed. In order to create a pleasant experience (in which consumers are not choking on leaf particles) matcha is milled incredibly fine, about ten times more fine than most coffee is ground. Particles this small behave less intuitively.

Matcha + Water

Matcha is a suspension

A whole green tea leaf put in hot water might bob at the surface for 30 seconds. As it absorbs water it becomes more dense than the surrounding liquid and sinks. But what if you cut the leaf in half? Then in half again? Eventually its behavior will start to change. The forces of Brownian Motion, or the random movement of particles in liquid, will start to have a stronger effect than the force of gravity weighing the matcha particle down. Gravity and Brownian Motion engage in an elaborate dance that creates a suspension. Eventually, gravity wins and the particle sinks to the bottom.

How long does this dance last? It depends on two main factors: particle size and particle shape.

Matcha particle size

Matcha should be imperceptibly small, both to the palate and to the naked eye. Different manufacturers or grinding devices yield different particle sizes which can result in very different products. Most matcha is between 5-20 microns, but can in theory go smaller. The industry seems to have consensus that between 5-15 microns is best and forms a very stable suspension.

If your matcha sinks to the bottom quickly it could mean that the particles are too big.

Are smaller particles better? Yes, to a point. The smaller the particle, the greater the surface area to volume ratio. Put another way, the electrostatic forces on the surface of the particles get proportionally stronger than the gravitational forces that would want to keep particles apart. These cohesive forces make the matcha stick to itself, which leads to a lot of clumps. These clumps can be harder to break apart in water when whisking and can also be a manufacturing nightmare due to the gummy texture it creates.

The primary purpose of whisking is to get the particles separated from one another to form a more uniform, heterogeneous mixture with the hot water. This is the case even if you pre-sift your matcha, which subdivides matcha clumps into smaller clusters.

Matcha particle morphology

Particle shape heavily influences the quality of any matcha suspension. Round particles have less surface area, and therefore less surface energy and sink more easily than jagged particles. When it comes to matcha, not all powders are created equal because of differences in milling technique.

Industrial ball mills are an incredibly efficient way to powder tencha into matcha. However, the resulting particle morphology is spherical. You can even feel the texture difference if you rub some culinary grade matcha between your fingers – it’s silky smooth. High-end, ceremonial grade matcha, milled on a traditional ishi usu (stone mill), will feel a bit more sticky and give more resistance.

Matcha milled on an ishi usu results in a jagged, high-surface-area particle shape. These particles form a significantly higher quality suspension and sink much slower. The tradeoff is in the speed of the milling process, yielding only 20-40 grams of tea per hour.

There is also a large tradeoff in temperature for varying milling methodologies. Milling anything to such a small powder requires a lot of force and therefore a lot of friction. Ishi usu mills grind incredibly slowly to keep the milling temperature low, whereas friction from the ball mills heat the tea quite considerably, damaging the flavor of the product. As far as we have researched, we cannot determine if there is a link between milling temperature and resulting morphology, but we suspect there is.

Differences in millstone pattern design can also influence the resulting shape of the matcha particle.

Water temperature

When you introduce a matcha particle to water it goes through a hydration process, taking in water to a point of saturation. The temperature of the water determines the speed of water intake. This intuitively makes sense – if we take loose leaf tea and mix it in ice water, it will float to the top and still be brittle enough to break even after a few seconds.

When whisking with cold or room temperature water it is more difficult to form a suspension of matcha particles because they are not fully hydrated. They also tend to clump up more easily.

Water temperature also has a huge impact on extraction and final flavor profile. A lot of the bitter catechins in Japanese green tea don’t start to become extracted until 80˚ Celsius. I highly recommend reading Tyas Sōsen’s blog article on modern Japanese farming practices, the Japanese preference for umami flavor in green tea, shading practices, and suggested modern brewing temperatures. There’s a fascinating link between fertilizer, shading, and optimal brewing temperatures.

Conclusions

Unlike other powdered beverages, matcha doesn’t dissolve. Whisking matcha is necessary because it creates turbulence to break apart the cohesive forces of the matcha particles and form a high-quality suspension. The multi-tine shape of a traditional Japanese bamboo chasen is remarkably good at creating the turbulence to have fantastic whisking power.

But it also has another benefit: creating the most under appreciated ingredient in great matcha: air.

Matcha + Air

Foam creation

Green tea contains natural surfactants called saponins, which are the key to creating matcha foam. From a scientific perspective, a foam is a two-state mixture of a liquid and gas. The foam “holds” the liquid up from the surface tension of the bubbles and naturally drains over time.

Matcha foam is glorious. It’s delicious and as important to the sensory experience of matcha as the rich head of a Guinness.

When you whisk matcha you start to incorporate air into the mixture, forming bubbles. The multi-tine design of a chasen creates narrow openings for bubbles to travel through, which further subdivides them to create froth.

Research from Sawamura et al demonstrated that matcha particles are also key in foam formation and stability. It was found that the number of available matcha particles in the suspension contributes to foam stability. These particles reside in the inner foam membrane. The researchers tested like-solutions with and without the presence of these particles and determined that their presence was critical to foam formation and stability. This is possibly because it increases the thickness of the foam membrane and makes it more robust. In other words, if you were to filter out the matcha particles in suspension, you would not see the amount and quality of foam that can normally be achieved.

Matcha to water ratio

Whisking matcha with too much water is probably the most common way to produce disappointing matcha froth. Leveraging the right ratio will result in higher-quality foam. Typically, two grams of matcha are whisked in 60 grams of water.

While we could not find any research on the quantity and quality of foam produced under different mixing ratios, we suspect that the mechanism is driven by the concentration of surfactants in the solution and the available matcha particles in the suspension. If anyone has any insights into this please let us know in the comments!

Water temperature

Water temperature is surprisingly important for foam quantity and quality. Sawamura et al discovered that the foaming effect of whisking matcha generally increases with an increase in temperature. This is partially driven by slowing down the drainage rate of water from the foam, which destabilizes it.

Additionally, the extraction of tea saponins, the primary surfactant agent in matcha, peaks at around 70˚C. This, in combination with the under-extraction of catechins (which contribute a bitter/astringent flavor), are further evidence that water temperatures around 70˚C are optimal for most matcha.

Whisking with cold water or room temperature water not only results in a low quality suspension, it doesn’t give enough time for saponin extraction, which further decreases the foaming potential when whisking matcha.

Foam stability and Ostwald ripening

Not all foam is created equal. Foam size and evenness are the primary factors that determine foam stability. The finer the matcha particles, the better the foam. Matcha particles contribute to foam formation and reside in the inner walls of the foam membrane. They make a protective coating and contribute to foam stability.

Foam size is correlated to foam stability. Subdividing bubbles during whisking will result in a a more stable and silk-textured foam. Smaller bubble sizes significantly reduce the drainage rate. Cutting the bubble size in half can have a 4x effect on draining time.

Foam evenness is also critical to foam stability due to a phenomenon called Ostwald Ripening. This effect states that smaller bubbles give their air to larger bubbles over time. Barista Hustle has a fantastic blog post about this effect and creating micro foam in milk when preparing lattes.

Conclusions

A high-quality matcha suspension will result in high-quality foam when whisked properly. Vigorous whisking with a chasen, or Japanese matcha whisk, helps create high-quality foam by subdividing the bubbles, which contributes to foam stability. For best results, it’s critical to whisk with hot water around 70˚C.

Shameless Plug!

Our team created a matcha whisking bowl optimized to create a high-quality suspension and amazing matcha foam. The elongated design allows users to whisk matcha much faster, more consistently, and with less strain than the standard zig-zag motion in a circular bowl. We call this One-Dimensional Matcha Whisking.

It sports other thoughtful design features as well - check it out here!