Stovetop Milk Steamer

Project Description

A conversion of the Bialetti Moka Express to a stovetop milk steamer. This project was inspired by Create's Stovetop Milk Steamer.

How it works?

The water in the bottom chamber exposed to heat will vaporize. According to Guy-Lussac's Law/Third Gas Law (p1/T1 = p2/T2), the pressure under constant volume will rise. Once the pressure is up, opening the valve will release the vapor into the milk-filled jug, and froth it.

The stovetop milk steamer has the following components:

• Pressure chamber - it is a reservoir of pressurized gas (vapor). Baristas usually froth milk for about 25 seconds, but in this case, you'll be limited by the Moka's bottom chamber size and the gas flow through the pipe. Therefore, a large chamber and small cross-section tube are desired.
• Valve for releasing the vapor
• Steam wand with nozzle

Nozzle

The nozzle I purchased had an uncommon thread - M7x0.75, which was hard to find anywhere, so I machined one with a lathe.

M7x0.75 thread

Machining the nut

Final result

Functionality Improvements

1. Monitoring Pressure and Temperature

   The device does the job, but reaching a consistent, satisfying result is unlikely. It is up to your skill and feel when to release the valve. You have no clue about the temperature in the chamber or if the pressure inside the chamber is sufficient when opening the valve. Given that, I suggest attaching a manometer and thermometer on the side of the bottom part. With this, you'd have some more control of what's going on inside.

2. Stability

   My Moka is made of aluminum and, therefore, very lightweight. While frothing the milk, you'll ideally hold the jug in one hand while opening the valve with the other. This device, however, it prone to tipping over, making it less enjoyable to use.

3. Characteristics

   Measuring the flow and pressure through the nozzle in real time would be fun. The data could further be used to improve the device, such as raising the pressure within the chamber by increasing the security valve's threshold/optimizing the wand diameter and nozzle design.

Gallery