06 · Basic · Intermediate
Milk Technique — Steaming, Texturing, Pouring
Air in briefly; refine it for a long time
Written by Chanho Hong
What this chapter covers
Steaming (frothing) explained as two phases — stretching, which introduces air, and rolling, which breaks it down — plus the textural differences between cappuccino, latte and flat white, temperature management, and why pouring changes the taste.
The quality of a milk beverage depends on how fine and how stable a microfoam is produced. Steaming becomes clear once it is understood as two phases: stretching, which introduces air, and rolling, which breaks that air down finely.
Steaming (Frothing) Basics — Stretching · Rolling
Milk steaming divides into two phases. Stretching is the phase (the opening seconds) in which the steam wand introduces air and increases the volume; Rolling is the phase (most of the time) in which that air is broken down finely by the rotating flow into microfoam.
Introducing air (stretching) is easy. What is difficult is breaking that air down finely in the rotating flow into a smooth microfoam (rolling). If rolling is insufficient, large bubbles remain, the milk splits along the grain and latte art is impossible.
At the start, hold the steam wand near the surface and introduce air lightly with a "hiss" (stretching), then immediately set the wand slightly off the axis of rotation so that the milk swirls (rolling). A loud "shriek" means the air is excessive.
"The longer you inject air, the better the foam" — a misconception beginners commonly fall into. Air injection (stretching) needs only the first few seconds; injecting for longer produces large bubbles and, if anything, makes latte art impossible. Most of the remaining time must be spent refining that air by rotation (rolling).
MTSPACE allocates steaming as 15% stretching : 85% rolling (that is, rolling carries roughly 5.6 times the weight). Air briefly, refinement at length — this allocation is the core of a smooth microfoam.
① Large bubbles keep forming. Air has been introduced for too long — finish the stretching briefly, in 1–3 seconds, and move straight into rolling. Keep the "hiss" short; a "shriek" is the signal of excess air.
② The foam and the liquid separate (splitting along the grain). Rolling is insufficient — set the wand slightly off the axis of rotation so that the milk swirls, and roll it thoroughly until the finish to refine the bubbles.
③ Diagnosis by sound. The state can be read from the steaming sound alone. The ideal is a light intake sound at the start (normal) → a quiet rotating sound (rolling under way); a "hissing" air sound throughout means the stretching is too long.
Texturing — Cappuccino · Latte · Flat White · Temperature
What separates the three representative milk beverages is, in the end, the thickness of the foam and the texture of the milk. With the same espresso, how much foam is laid on and how it is laid on determine the identity of the drink.
| Beverage | Foam thickness | Textural character |
|---|---|---|
| Cappuccino | Thick (traditionally ↑) | Large foam proportion; light particle feel and volume |
| Latte | Thin | More milk and thin foam; soft and mild |
| Flat White | Very thin (microfoam) | Milk and foam fused into one; silky, the espresso emphasised |
The amount of stretching (air) sets the foam thickness. A cappuccino takes more air for a thick foam, a flat white minimises air for a thin, fused microfoam, and a latte sits between the two. On the same quality of rolling, only the amount of air is adjusted.
The recommended finishing temperature is 55–65℃ (60℃ recommended). Going beyond 60℃ to 65℃+ denatures the protein, so sweetness decreases and foam stability falls. If the hand holding the pitcher is too hot to keep in place (63℃+), stop immediately.
"Hotter is better" does not hold. Overheating (70℃+) destroys the sweetness and flavour of the milk. The natural sweetness of milk comes through best around 60℃.
① A flat, watery latte. Most likely the milk was overheated (70℃+) so the sweetness died, or the foam is coarse. Stopping at 60℃ and rolling sufficiently brings the natural sweetness and silkiness back out of the very same milk.
② Adjusting foam thickness by beverage. On the same quality of rolling, change only the amount of air (stretching) to make a cappuccino (thick foam), a latte (thin) or a flat white (microfoam). For a request to "bring the espresso out more", minimise the foam with a flat white.
③ Handling alternative milks. Oat and soy milks have a different protein structure, so foam stability is lower. Using a barista-edition alternative milk and setting the finishing temperature lower, at 55–60℃ (overheating causes separation and a beany off-smell), stabilises the microfoam.
Pouring Technique — Crema Stability · Pre-mixing · How the Taste Changes
Pouring is the stage in which microfoam is poured over the espresso to draw a pattern while, at the same time, how the milk and the coffee are mixed determines the final taste.
The crema is the canvas of latte art. The thicker and more stable the crema, the crisper the pattern and the longer it lasts. A freshly pulled espresso, a correct extraction and a pour that starts slowly from a low position break the crema less.
A technique in which, before the pour proper, a small amount of milk is poured from a high position so that it mixes with the crema first. It tidies the surface colour to create contrast and homogenises the milk and coffee in advance, giving a balanced taste from the first sip.
Flavour Difference — even with the same espresso and milk, the way they mix changes the taste. Homogenised by pre-mixing, the cup is harmonious from the first sip; merely laid on the surface, layer separation makes the milk jump out at first and the coffee later. Foam thickness (texture) and mixing (the pour) together create the final balance.
① A cup that is watery on the first sip and bitter at the end. This is due to layer separation. Mixing the crema and milk first by pre-mixing and then laying the pattern on top keeps the appearance intact while balancing the cup from beginning to end. Appearance and taste are reconciled through the order of the pour.
② When the crema is weak and the pattern will not show. Thicken the crema with a freshly pulled espresso and a correct extraction, and start slowly from a low position so that the crema is broken less. Once the canvas is stable, the detail becomes crisp.
③ Standardising across the shop. If the latte tastes different from one staff member to the next, unify whether pre-mixing is used and the starting height of the pour in an SOP to homogenise the balance of the cup. Texture (foam thickness) and mixing (the pour) together create the final taste.
Questions this chapter answers
- What ratio of stretching to rolling should I use?
- The MTSPACE standard is 15% stretching to 85% rolling. A few seconds of air is enough; introduce it for longer and you get large bubbles that will not pour. The rest of the time should go into refining that air by rotation, which is what produces smooth microfoam.
- What separates a cappuccino, a latte and a flat white?
- The volume of milk and the depth of the foam. A cappuccino carries thick foam; a flat white has thin, dense microfoam and a lower milk ratio so the coffee stays present; a latte sits between them with the highest proportion of milk. From the same pitcher you control this with stretching time and cup size.
- How hot should the milk be?
- Take it too high and the proteins denature: sweetness disappears and a cooked note appears. Stop while the sweetness of the lactose still reads, and finish slightly below your target — the temperature continues to rise a little while you pour.
Figures and regulations are verified against a source hierarchy: Tier 1 in-house knowledge base → Tier 2 SCA·WBC and peer-reviewed literature → Tier 3 web. Anything not adequately supported is marked [to verify] in the text.