Everything specialty coffee believes about espresso machine temperature & pressure is wrong

For years, specialty coffee has become increasingly precise in the way it measures espresso. We weigh coffee to a tenth of a gram, calculate extraction yield to two decimal places, analyse water chemistry, refine burr geometry and spend countless hours adjusting recipes that may differ by only a fraction of a degree or a second.

That pursuit of precision has made our industry better. Undoubtedly.

But I believe there’s one assumption we’ve accepted without questioning it closely enough.

When an espresso machine displays a brew temperature of 93°C, are we certain that’s the temperature the coffee actually experiences?

I’m not asking whether modern espresso machines are inaccurate. I’m asking whether we’re measuring the part of the brewing process that ultimately shapes extraction.

Those are different questions.

Over the past several years I’ve spent a great deal of time studying what happens inside an espresso machine while it’s brewing. The more I investigated, the more I began to wonder whether we’ve become comfortable treating a single measurement as though it describes an entire brewing system.

As an engineer, I’ve learned to be cautious whenever a complex system is reduced to one number. Sometimes that simplification is entirely appropriate.

Sometimes it isn’t.

What does an espresso machine actually measure?

An espresso machine doesn’t directly measure the temperature of the water reaching the coffee. It measures the temperature where its sensor is installed.

Those aren’t the same thing. And that distinction sits at the centre of my research.

Look at any modern espresso machine and you’ll find a display showing the brew temperature. Most of us naturally assume that number represents the water flowing through the coffee puck.

In most machines, it doesn’t.

The sensor is usually located somewhere inside the machine itself. Depending on the design, it may be attached to the boiler, positioned inside a thermowell or placed close to the heating element.

It’s measuring the temperature where it sits. Nothing more.

That doesn’t make the measurement wrong. It simply tells us one part of the story.

Imagine trying to describe the weather across an entire city using a single thermometer. The thermometer may be perfectly accurate. It still can’t tell you what’s happening everywhere else.

Espresso machines deserve the same way of thinking. If we’re measuring temperature at only one point, what can we confidently say about the rest of the brewing system?

That’s the question that first drew me into this research.

An espresso machine is a moving system

It’s easy to think of an espresso machine as something that reaches its target temperature, settles into equilibrium and then repeats the same process over and over again. But anyone who’s spent time behind a busy espresso bar knows it doesn’t quite work like that.

Fresh water continually enters the boiler. Hot water leaves. Heating elements cycle on and off. Steam is generated. Metal components absorb heat and release it again. Every shot changes the thermal conditions inside the machine while the machine is already preparing for the next one.

An espresso machine isn’t a container filled with perfectly uniform water. It’s a thermal system that’s constantly balancing heat transfer, water flow and pressure.

That doesn’t mean it’s unstable. It means stability is something the machine has to maintain continuously.

Once I started looking at espresso machines through that lens, a series of practical questions followed naturally.

What is the temperature at the top of the boiler? In the middle? And what happens near the bottom, where fresh water enters? How much does the outlet temperature change between consecutive shots? What temperature reaches the group head? Most importantly, what temperature reaches the coffee?

These aren’t abstract questions. They’re measurable ones. Yet most of us never measure them.

Instead, we’ve accepted one temperature reading as representing the entire system. I’m convinced that’s not enough.

Brew temperature shapes extraction

These questions only matter because brewing temperature has a direct influence on flavour.

Everything we do as baristas eventually comes back to controlling how water extracts soluble compounds from roasted coffee. Acids, sugars, aromatic compounds and bitter compounds dissolve at different rates. Small changes in brewing temperature alter that balance, changing sweetness, acidity, body and bitterness in the cup.

Every experienced barista knows this instinctively.

The ideal brewing temperature for one coffee rarely produces the best result for another. Recipes change because coffees change.

This is why brewing temperature has become such an important part of espresso preparation, and why the specialty coffee industry measures brew water temperature within the brew path when evaluating commercial espresso machines rather than relying solely on the temperature shown on the display.

I’ve always thought that’s significant. It recognises that the easiest measurement isn’t always the most useful one.

A display tells us what one sensor detects. It doesn’t automatically tell us the temperature experienced by the coffee.

One measurement can’t describe an entire brewing system

One lesson engineering teaches is that complex systems rarely reveal themselves through a single measurement.

Espresso is no different.

Specialty coffee has become very good at reducing complicated processes to practical numbers. Ninety three degrees. Nine bar. A one to two brew ratio. Twenty percent extraction yield.

Those numbers are enormously useful. They allow us to communicate, compare recipes and repeat good results. I rely on them every day. But useful measurements also have limits.

Inside an espresso machine, water is moving. Heat is moving. Pressure is changing. Metal stores thermal energy and releases it over time. Different parts of the machine respond at different speeds.

Modern commercial espresso machines manage those variables remarkably well. Their thermal stability is vastly better than it was even fifteen or twenty years ago.

I’m not questioning that. What I am questioning is whether we’ve become comfortable allowing one measurement to stand in for an entire system.

Good measurements simplify complexity. They shouldn’t persuade us that the complexity no longer exists.

Pressure deserves the same attention

The same line of thinking led me to pressure.

Ask almost any experienced barista how much pressure is used to brew espresso and you’ll hear the same answer. Nine bar.

Pressure has become one of the defining numbers in espresso. For good reason.

It influences how water moves through the coffee bed, how quickly compounds dissolve and how extraction develops throughout the shot.

But pressure also exists throughout a brewing system rather than at a single point. That made me wonder whether we might be simplifying pressure in much the same way we’ve simplified temperature.

During my own measurements, I observed occasions where pump pressure remained close to nine bar while boiler pressure varied between 5.1 and 13.3 bar. During those same tests I also recorded changes in total dissolved solids and extraction yield.

Those observations shouldn’t be overstated. They don’t prove that changes in pressure caused the differences in extraction. Espresso contains too many interacting variables to draw that conclusion from a single series of tests.

But they do raise a question I don’t think we’ve answered.

If different pressure measurements within the same machine don’t always behave in the same way, which one best represents the conditions experienced by the coffee?

I don’t know the answer. But it’s worth looking into.

Sometimes identical recipes produce different espresso

Every barista has experienced a shot that doesn’t quite make sense.

The grinder hasn’t moved. The dose is unchanged. The yield lands exactly where it should. Shot time looks normal.

Yet the espresso tastes different.

Perhaps it’s sweeter. Or perhaps the acidity is slightly brighter. Or the finish carries a little more bitterness than the shot before it.

Our instinct is usually to look outside the machine. Coffee changes as it rests. Humidity changes throughout the day. Grinders retain coffee differently. Puck preparation is never perfectly identical.

Those are all sensible explanations. I’ve relied on them myself for years. But I’ve gradually come to wonder whether they’re always the complete explanation.

If the brewing conditions inside the machine also vary slightly from shot to shot, perhaps some of that variation begins before the water even reaches the coffee.

That’s still a hypothesis. If future research proves me wrong, I’ll be perfectly happy with that outcome.

A good hypothesis isn’t something to defend. It’s something to test.

What I mean by “machine luck”

One phrase I’ve used to describe this possibility is machine luck. It’s also the phrase that’s most often misunderstood.

I’m not suggesting espresso competitions are random. And I’m not questioning the skill of competitors or the consistency of judges.

I’m asking a much narrower question.

Imagine two competitors using the same coffee, the same grinder and identical recipes. Both prepare exceptionally well. Both execute their routines almost perfectly.

If the brewing conditions delivered by the machine differ slightly between those two routines, the espresso itself may also differ.

The judges would simply evaluate what they taste. If variation exists, it would already be in the cup before judging begins.

Whether those differences occur often enough to influence competition results remains unknown. At the moment, I don’t think we have enough evidence to answer that question confidently.

The research I’d like to see

I’m not here to make a conclusion. I’m here to invite the specialty coffee industry to do an experiment with me.

Imagine measuring temperature at multiple locations throughout the brewing system. The top of the boiler. The middle. The bottom. The outlet. The water immediately before extraction.

Now measure pressure throughout the same system. Record total dissolved solids. Measure extraction yield. Carry out blind sensory evaluations.

Repeat exactly the same recipe across dozens, perhaps hundreds, of consecutive shots using the same coffee, the same grinder, the same dose, the same yield and the same machine.

That study would tell us far more about espresso consistency than we can learn from a single temperature display.

Perhaps it would confirm that our current assumptions are largely correct. Perhaps it would reveal variables we’ve never measured before.

Either outcome would improve our understanding of espresso.

The question I’d like the industry to ask

One of the things I’ve always admired about specialty coffee is its willingness to question its own assumptions.

We’ve questioned roasting. Grinding. Water chemistry. Extraction.

Each time we’ve asked better questions, our understanding has improved. Sometimes the evidence confirmed what we already believed. Sometimes it forced us to rethink it.

I think espresso machine measurement deserves the same curiosity.

Not because I believe today’s machines are fundamentally flawed. They’re extraordinary pieces of engineering. Nor because I think everything we’ve learned about espresso needs to be rewritten.

I simply think we’ve become comfortable treating one measurement as though it describes an entire brewing system.

Perhaps that’s correct. Perhaps it isn’t. I don’t know.

What I do know is that every espresso begins as water travelling through a remarkably complex machine before it ever reaches the coffee. If we want to understand extraction as completely as possible, we should understand that journey just as thoroughly.

Good measurements simplify complex systems. They shouldn’t persuade us that the complexity no longer exists.

Frequently asked questions

Does an espresso machine measure the temperature that reaches the coffee?

Not directly. Most espresso machines measure temperature where their sensor is installed, such as the boiler or another internal component. Depending on the machine’s design, that measurement may differ from the temperature of the water that ultimately reaches the coffee puck.

Is the brew temperature shown on an espresso machine always accurate?

The displayed temperature can accurately represent the sensor’s reading. The article argues that accuracy is different from representativeness. A single sensor may not fully describe the thermal conditions throughout the entire brewing system.

Why is espresso machine temperature important?

Brew temperature directly influences coffee extraction. Even small changes in water temperature can affect how acids, sugars and other soluble compounds dissolve, changing sweetness, acidity, body and bitterness in the final cup.

Why can identical espresso recipes produce different results?

Several variables can contribute to shot-to-shot variation, including coffee age, humidity, grinder retention and puck preparation. The article also explores the possibility that small changes within the espresso machine itself may contribute to differences in extraction, although it does not claim this has been proven.

What is thermal stability in an espresso machine?

Thermal stability describes how consistently an espresso machine maintains brewing temperatures during repeated use. Modern espresso machines achieve excellent thermal stability, but the article suggests that measuring temperature at multiple locations may provide a more complete understanding of brewing conditions.

Does pressure affect espresso extraction as well as temperature?

Yes. Pressure influences how water moves through the coffee bed and contributes to extraction. The article argues that, like temperature, pressure exists throughout the brewing system and may deserve more comprehensive measurement than a single reading.

What research could improve our understanding of espresso machine temperature?

The article proposes measuring temperature and pressure at multiple points throughout the brewing system while brewing repeated shots under identical conditions. Combining these measurements with extraction yield, total dissolved solids and blind sensory evaluation could provide a more complete understanding of espresso consistency.

Who is Ajeyudu Pathuri?

Ajeyudu Pathuri is a dedicated coffee professional with over 15 years of experience across the coffee value chain. Since 2017, he has served as an Authorized SCA AST and a certified Q Arabica Trainer. He has calibrated more than 10,000 coffee machines and has conducted extensive research on brewing methods and equipment performance.

His first invention, created in 2017 using parts from a toy helicopter, led to a patented extraction stage controller that changed how water pressure was regulated. In 2019, he developed a multi directional water flow system for automatic machines, patented in 2024, which reduced waste and gave baristas more control during calibration.

His most recent and most significant invention, developed in 2023 and patented in 2025, was inspired by the shape of an Indian curry bowl. It solves the longstanding problem of water instability inside espresso machines. By stabilizing water density, temperature, and steam behavior before the water reaches the puck, Ajeyudu’s system dramatically improves extraction consistency and cup quality.

Ajeyudu continues to contribute to the global coffee community through science, research, and a deep commitment to practical problem solving.