Many friends know I've been working on my x project, a mechanical variable-pressure espresso machine. Modifying a commercial grinder's flat burr and fitting it into a manual grinder to push the boundaries of hand grinders brought me great satisfaction. Now, I want to do it again by adding adjustable pressure to an espresso machine, giving people more freedom to craft their unique espresso.
After developing three prototypes, I discovered the MUVNA Mach espresso machine. Although their design and mechanical structure are quite different from mine, MUVNA’s machine achieved the freely adjusted pressure function I aimed for. I immediately paused my x project and secured the rights to sell this machine.
1. My Notion of Espresso Extraction
My notion for making espresso is: Excellent Espresso Extraction = Even Extraction × Segmented Extraction. Even extraction is the foundation for a quality espresso, and segmented extraction opens up endless possibilities for flavor exploration, making espresso more exciting.
Even Extraction
Even Extraction is a holistic view. Every coffee particle in the basket has a different extract yield rate — this is determined by the coffee particle size, particle position, basket structure, and water characteristics, none of which can be changed.
Even Extraction refers to keeping the amount of over-extracted and under-extracted below the threshold of human perception, at the same time, the bitterness and off-flavors of over-extraction, and the sourness and astringency of under-extraction, to be offset by the properly-extracted flavors. In short, all particles need water to flow through them continuously, plus the good ones neutralize bad flavors. One practical rule is to avoid channeling — keep the water from numerous small uniform channels through the coffee puck instead of one to three big channels.
Segmented Extraction
Segmented Extraction is a process perspective. In reality, the different flavors in the coffee puck—acidity, sweetness, bitterness, and off-flavors—are extracted sequentially. Tetsu Kasuya's 4:6 brewing method inspired this idea.
By breaking extraction into stages and adjusting variables for each phase, you can manipulate the extraction yield and rate at each stage, creating more possibilities and flavors.
2. Pressure Variables and Variable-Pressure Espresso Machines
In espresso extraction, pressure serves three main functions:
Pre-Infusion
Using 0.5 to 3 bar of pressure, the water quickly saturates the tightly packed coffee puck.
Adjusting Flow Rate
A 6-bar pressure will result in a faster output flow rate than 5-bar, and the flow rate will peak at 9 to 10 bar.
Altering the Puck Structure
During extraction, lower pressure than higher pressure results in a more stable coffee powder structure, reducing the likelihood of channeling.
Advantages of a Variable-Pressure Espresso Machine
Traditional machines that fix 9-bar pressure only allow the puck to adapt to that pressure, producing a peak output flow rate based on the puck resistance. A variable-pressure espresso machine can adjust the pressure to accommodate different grinding sizes of powder in the basket, keeping the puck structure dynamically stable; it can also adjust flavor ratios during various extract phases, achieving Even Extraction and Segmented Extraction intuitively.
3. Why I Chose a Mechanical Variable-Pressure Espresso Machine
My coffee philosophy is, getting people as involved as possible in the extraction process to gain freedom and fun, so I naturally gravitate toward non-electric mechanical espresso machines. However in product development, you have to evaluate input vs. output, the best approach is often to modify existing mature models at a lower cost. Here’s my breakdown of the different machine types available:
Water Pump Machines – Abandoned
Electric water pump machine is a highly complex multi-space control system. Dividing the water road from Boiler to Group Head into multiple space sections, controlling water volume, flow rate, temperature, and pressure at each section separately using software, pumps, sensors, and valves. Precisely adjusting the pressure on a water pump machine is beyond my development ability; it is difficult to fully sync the water volume and pressure entering and leaving the Ghoup Head, and it is very counterintuitive to use. So, I decided to drop the idea.
Air Pump Machines – Abandoned
Mechanical or electric air pump machines are a single-space control system. The air and water share the same chamber. It adds pressure like a bike pump, but it has difficulty with precise pressure reduction via precise air release.
Piston Machines – The Way Forward
Mechanical or electric piston machines are a single-space control system. The piston and water are in the same chamber. The piston moving inside the water-filled chamber generates pressure, perfectly synchronizing water and pressure change. This is highly intuitive.
In Spring-Lever-Piston machines, the pressure automatically decreases, though the drawback is that the pressure curve can’t be modified. Lever-Piston machines allow for manual pressure control, but they require a lot of effort and can’t provide precise pressure adjustments. However, the mechanical structure can be modified to make pressure control more accurate and less dependent on the user’s strength. That’s why I chose a mechanical piston machine as the development direction for my X project.
4. The Innovative Design of the Mach Machine
I think Mach is a Freely Adjust Pressure Mechanical Espresso Machine. It has creatively improved the piston mechanism, expanded the hardware ability boundary, and offered intuitive, adjustable pressure control.
People should be the primary focus for non-electric mechanical machines. That means that in human-machine interaction, Non-electric mechanical machines can compensate for or overcome people's physical limitations. My ideal of Freely Adjust Pressure = No-Limits Adjust Pressure × Precisely Adjust Pressure.
No-Limits Adjust Pressure
When using Lever-Piston Espresso Machines, your strength can limit extraction. For example, if I can only push 7 bars of pressure with a lever-piston maker, my strength becomes the bottleneck to hitting 9 bars. Plus, when I hit a pressure between 1 and 9 bars, I can’t let go because I have to keep countering the lever’s force, or the piston will lift, and the pressure will drop fast.
The Mach machine's mechanical design allows people to reach 12 bar effortlessly. You can also release the pull-rob without losing pressure. You could exert more effort to push it to 16 bar, but that's forbidden as it might deform your filter basket. That mechanical design breaks people's physical limitations and gets No-Limits Adjust Pressure.
Precisely Adjust Pressure
The pressure change is almost linearly related to the piston’s movement in a single confined space. Two things are essential to achieve precise pressure control in a non-electric machine: 1. minimizing the piston’s movement distance; 2. matching the precision of human operation.
Like the infinitely grind adjustment on a top-tier coffee grinder, Mach’s innovative mechanical gear system allows infinitely fine-tuning piston movement distance. Turning the rotary handle moves the piston just 2mm per complete turn, and it takes 24 turns to move the piston from top to bottom. Like driving a car, you turn the steering wheel 10 degrees to control the direction, which is a precision comfortable for human operation. Mach’s rotary handle works like the steering wheel—half a turn moves the piston only 1mm, perfectly aligning human intuition with mechanical precision. Mach adjusts pressure precisely and quickly to enable segmented extraction ease.
5. Demonstration of Segmented Extraction with Mach
The video showcases the exploration of segmented pressure extraction with a Mach espresso machine.
Light Roast - 4-Stage Pressure Extraction
Stage1--1bar; Stage2--12bar; Stage3--9bar; Stage4--6bar
Light roast beans have low extractability, so I used a finer grind level with the ORCA-GO flat burr. I wanted to extract more flavor while minimizing channeling.
Stage1 1 bar pre-infusion ensures the light roast puck isn't broken; Stage2 12 bar tightens the puck, extending extraction time and enhancing flavor; Stage3 9 bar increases the flow rate; Stage4 6 bar prevents channeling.
Dark Roast - 2-Stage Pressure Extraction
Stage1--0.5bar; Stage2--2bar
Dark roast beans have a high extract yield rate, so I used a coarser grind with the ORCA-GO ghost burr. I aimed to reduce the bitterness of dark chocolate and create a clean taste, similar to pour-over coffee.
Mach has a 120ml water chamber, max to 1:5 ratio of 18g bean, which can produce highly TDS pour-over coffee. Alternatively, you can adjust the TDS by using the bypass method. I forgot to add filter paper at the bottom of the basket in the video. It helps remove oils and makes the taste cleaner.
6. Explore Espresso with Mach Variable Pressure Machine
I’m so excited to recommend the MUVNA Mach Mechanical Manual Espresso Machine. Not only is it intuitive to use, but it also allows individuals to explore espresso on a deeper level more freely. Perfect for experienced and ambitious adventurers. Well, free a moment, and have fun!