I feel like I’m hitting a glass ceiling. The coffee is good but not great. I’m trying to fine-tune. But the whole system is unstable. The flow rate is rather solid, but the taste changes with each shot. Time to take a step back and think.

Upgrades

I’ve already made several upgrades to my setup / process. Each upgrade improves the final result and/or its consistency. Upgrades also cost money and I hate to admit that my budget is not unlimited. Let’s be smart and perform the upgrades that give me the most bang for the buck.

There are several potential upgrades. I have already done some of them. Here’s a little table.

The spray bottle wins if you ask me.

What is an OPV?

Glad you asked! Let’s talk about brewing pressure. Coffee machines should create a certain pressure profile while brewing. I say profile, because there are machines that vary the pressure during one brew. Pre-infusion is one instance of this. However, all of this is in the early stages of research and until proven the contrary let’s assume that there are only two things that matter: Achieving a certain pressure value during a shot and being consistent.

The ideal pressure is 9 bar. There’s no good scientific explanation for this value. As far as I know, there have been tests and 9 bar is the pressure that achieves maximum extraction. Let’s accept it for now since the whole industry seems to agree on it. If your pressure is lower, you’ll see less extraction. If it is higher, you’ll see faster flow rates. People report that this makes it significantly harder to dial in an espresso.

The Gaggia classic has a vibration pump with a rated pressure of 15 bar. The machine controls its target pressure via an over-pressure valve (OPV). Here’s some bad news: The stock OPV opens at 12 bar, resulting in around 12 bar of pressure while brewing. Gaggia chose 12 bar instead of 9 because they want to make our lifes miserable and apparently that’s a good pressure for pre-ground coffee in a pressurized filter basket. I guess that’s the most common setup people use. But we’re not savages, so we use a non-pressurized basket that needs 9 bar.

Fortunately, it’s simple to change the OPV. In fact, the part that controls under which pressure it opens is a little spring. You can replace it with a weaker spring to have it open at a lower pressure. These springs can be purchased for no money on the internet and installed in 10 minutes.

PIDs

PIDs are the first mods that were done on home espresso machines. Back then, people thought that a stable water temperature while brewing would lead them to perfect espresso shots. We know today that it takes more than that, but a stable and configurable water temperature is essential in reliabilty and reproducability.

Espresso machines have a boiler with a temperature sensor. The simplest way to keep a steady temperature is to define a maximum and a minimum temperature, heating when the temperature falls below the minimum until it hits the maximum. Machines without a PID do exactly that. Usually with the help of a mechanical thermostat (imprecise).

This results in a phenomenon called temperature surfing. Sounds like great fun, but it isn’t. The temperature of the machine oscillates between the heating cycles, making it basically guesswork to know when to pull a shot to “hit the wave” correctly and have the desired temperature.

What a mess, but PIDs are here to the rescue. PID (Proportional–Integral–Derivative) is a smart way regulate a physical quantity using a feedback cycle. It’s a mathematical formula that drives the heater in the boiler such that the temperature stays as close to a certain target value as possible.

The upgrade consists of an electronic thermostat, a microchip and a switch. The microchip measures the boiler temperature with the thermostat and then uses the switch to control the heating element of the boiler according to the PID formula.

The result is a very stable brew temperatures, within 1 degree celsius. People have reported massively improved consistency and quality (depending on the bean) using a PID.

Gaggiuino

I didn’t have a stroke while typing “Gaggia”, it is really spelled like this. The Gaggiuino (Gaggia + Arduino) is the most feature complete mod of the Gaggia Classic that exists. It adds a pretty strong microcontroller to the machine and lets it control the heating and the pump. Furthermore, it adds a pressure sensor and a heat sensor.

Sounds simple, but this is enough to bring the Gaggia from zero to hero. It includes:

• PID control of temperature
• PID control of pressure (pressure profiles, pre-infusion)
• A touchscreen that shows all sorts of stats during a shot
• Shot timers
• A mathematical estimation of the amount of produced coffee in grams (quite accurate)
• Support for hardware scales
• Support for bluetooth scales
• Wifi support (yeah wtf)
• And so much more

Action

If I want better coffee, I need a PID and the OPV mod. I’ve asked ChatGPT once more and according to the Reddit posts it found (or hallucinated, who am I to judge) people found it way easier to dial in a bean on modded machines. So the smartest choice is those two mods.

But I’m not smart. I’m a kid with a credit card. The Gaggiuino mod is already ordered. It should transform my machine into a beast. Until then I’ll do no more big tests, because I feel like I’m fighting windmills.