First Aid: Milk & Foam

← Back to the First Aid overview

Silky microfoam comes mostly from technique and care. Here you’ll find typical problems with the Subminimal NanoFoamer and the Rhino thermometer, with safe steps that follow the manufacturer’s guidelines — plus the Flick, Subminimal’s WDT tool for the coffee bed.

⚠️ Before you start: We show steps based on the manufacturers’ information — cleaning, changing the impeller and NanoScreen, adjusting the thermometer; where something comes from our own experience, we say so. The NanoFoamer PRO jug is not waterproof: never submerge the lower part, rinse it upright instead, and don’t put any parts in the dishwasher. Never open the base or electronics. No steam from your espresso machine? That belongs in the machine guide.

1. “The NanoFoamer no longer froths, makes noises — or won’t turn on”

  1. V2/Lithium: check the batteries or battery charge. The impeller is officially user-replaceable — just unscrew it.
  2. PRO Gen-2 with whistling or too little foam: first check the impeller and NanoScreen for damage, then turn the lid button up to 6 clicks clockwise until the magnetic NanoScreen couples cleanly.
  3. PRO with no power: seat the jug correctly on the base. If the logo doesn’t flash straight away, that’s normal according to Subminimal — the system needs a few seconds to restart, and the jug works anyway. Press the touch button firmly with your whole finger or thumb, if necessary a little higher, lower or right in the middle.
  4. Thoroughly clear the NanoScreen and impeller of milk residue.

Sources: Subminimal — NanoFoamer Gen-2: Spinout Troubleshooting · Subminimal — NanoFoamer PRO: No Power · Subminimal — Changing the impeller (V2/Lithium)

NanoFoamer PRO Quick Start Tutorial · subminimal

Manufacturer videos on YouTube. They only load when you tap them.

Stop line: Never open the PRO base, heating element and electronics; the V1 impeller is not replaceable according to the manufacturer.

Supplies: replacement impellers & NanoScreens — just ask us, we keep them in stock.

2. “The milk foam won’t turn silky — too coarse, too runny or too hot”

  1. Rinse the NanoScreen right after every use and let it spin briefly in water.
  2. Soak clogged screens overnight in lemon juice (or lemon with baking soda), then clean them with a stiff brush — replace worn screens.
  3. Use fresh, cold milk — according to Subminimal, opened cartons of plant milk also foam less well after a few weeks. On the PRO, choose the right programme and the flow controller for each milk: black for cow’s milk, blue for most plant milks, green for difficult varieties.
  4. Keep an eye on the temperature: the PRO beeps at around 60 °C and shows “OK”; if the jug stays on the base, it heats up to around 70 °C and then stops by itself.

Sources: Subminimal — Guide to Cleaning NanoScreens · Subminimal — Microfoam with the NanoFoamer PRO Gen-2 · Subminimal — Fresh Milk is Key

Stop line: Don’t “pry open” the screens — replacing them is cheaper than a scratched impeller chamber.

Understand & practise: Milk Foam Simulator · Pitchers: barista pitchers

3. “The Rhino thermometer reads incorrectly”

  1. Check against a reference: ice water must read 0 °C, boiling water (at sea level) 100 °C.
  2. If it’s off: adjust the calibration nut on the dial with the calibration tool — clockwise raises the reading.
  3. After adjusting, cross-check again with ice water.

Source: Rhino Coffee Gear — How to Calibrate Your Thermometer

Stop line: Don’t take the thermometer apart — only the calibration nut.

Accessories: Rhino Coffee Gear

4. “On the Flick, the needles jam or no longer retract”

The Flick from Subminimal is a WDT tool: you use it to loosen the coffee grounds in the basket before you tamp.

  1. Open the cap and clear the fine channels the needles run in of coffee grounds, using a toothpick or the tip of a knife. Then carefully reassemble everything.
  2. If the needles still jam or the button pops out: open the cap as you would to change the needles and tighten the screw inside that holds the button and magnet.

Sources: Subminimal — Fix non-retracting needles (Flick) · Subminimal — Troubleshooting your Flick WDT Tool

CHANGING THE NEEDLES ON THE FLICK WDT · subminimal

Manufacturer videos on YouTube. They only load when you tap them.

Stop line: Don’t bend the needles — replace bent needles.

5. Practise foam technique — before you doubt the device

Coarse bubbles, no pattern, milk separating? Usually it’s the amount of air, the temperature or your pouring technique — not the device. Our interactive tools show you live which adjustment does what:

Milk Foam Simulator (air, temperature, milk type) · Latte Art Trainer (pour height, flow, pattern)

6. “The steam wand, milk jug or frother smells rancid or feels sticky”

  1. Don’t guess, clean: a milk-system cleaner dissolves dried-on milk proteins and fats. Urnex developed the alkaline Biocaf Milk Cleaner specifically for residues of cow’s milk and plant milk (oat, almond, soy).
  2. Steam wand/jug: mix 30 ml of cleaner with 500 ml of warm water in the jug, submerge the wand, let it work for 15–30 minutes.
  3. Automatic frothers: mix 30 ml of cleaner with 500 ml of water, run the solution completely through the system, then repeat the same with clear, cold water.
  4. Afterwards, rinse thoroughly with clear water and run a short steam burst or rinse cycle without cleaner.
  5. To prevent it: wipe the steam wand with a damp cloth and purge it briefly right after each frothing (La Marzocco), rinse the NanoFoamer after every use (Subminimal). In our experience, do the deep clean about weekly instead of only once there’s a smell.

Sources: Urnex — Biocaf Milk Frother Cleaning Liquid (Alkaline) · La Marzocco — Linea Micra Manual (PDF) · Subminimal — Guide to Cleaning NanoScreens

Biocaf Alkaline Milk Frother Cleaning Liquid · Urnex Brands

Manufacturer videos on YouTube. They only load when you tap them.

Stop line: Formulated exclusively for milk-system components — not for the group head (use Cafiza for that) and not for limescale in the boiler (use the brand-appropriate descaler for that, see Water & Descaling).

Supplies: Urnex Biocaf Alkaline Milk Cleaner 1L — one formula for cow’s milk and plant milk, biodegradable and phosphate-free.

Nothing helped? Then it’s over to us.

Fastest line, around the clock: Ask Jackson, our AI advisor in the chat here on the website — he helps you right away with any question — from product recommendations to troubleshooting.

For anything beyond that — or if it’s a warranty case — this helps us help you without rounds of back-and-forth:

  1. Reply to your order confirmation — that way we have your order number right at hand. (Can’t find the email? Write to [email protected] and give us your order number.)
  2. Device & purchase date: model, serial number (a photo of the type plate is enough), purchased on …
  3. Description of the fault: what exactly happens, since when, how often?
  4. What you’ve already tried: which steps from this page?
  5. Photos & videos: of the problem — for noises please send a video with sound. Large videos (over ~20 MB) as a link.

We’ll get back to you within 1–2 business days. Prefer in person? Book an appointment or drop by in Zurich & Bern.

Email template (just fill it in):

Order number: #
Device (brand + model):
Serial number (see type plate):
Purchased on:
Problem since:

What exactly happens:

What I have already tried (steps from the First Aid page):

Attachments: photo of the type plate / photo or video of the problem

Your statutory warranty and guarantee rights remain unaffected — the First Aid steps are voluntary and only a recommendation. Important: if you discover a defect, please report it to us promptly.

Was this page helpful?

Next: Espresso machines · Grinders & scales · Cleaning & care · All tools