Over coffee about water, or how flavor is created in the cup

At my favorite coffee shop, the cappuccino put the world to rights. When I bought the same beans for home and brewed them on a pretty good equipment, the cup told a different story. The grain is the same, the recipe is the same, so where is the difference? This dissonance became the beginning of a conversation about how an invisible drop of minerals can build flavor. I talked about the trials and errors of restoring water quality for coffee flavor with Pavel Siemaszko, who over years of practice has developed a system for stabilizing water parameters to preserve the taste and aroma of the black beverage in the cup.

Agnieszka Hobot: What made you get into coffee brewing water parameters in the first place? When did you realize that water was the critical “missing link” in cup quality – and what assumptions did you make at the start?

Pavel Siemashko: The beginning of this story goes back about 15 years, the time when I moved from Warsaw to Gliwice. In the capital I worked as a barista and ran a café. I also opened my own place in Silesia. Very quickly I noticed that the same coffees brewed in Gliwice taste noticeably different – just worse. Since we operate in the specialty coffee segment, where the quality of the raw material and the precision of preparation directly translate into the taste in the cup, I began to systematically analyze the processes and look for the cause. I knew that the local water was characterized by high hardness, while the solutions proposed locally did not meet my expectations. Suppliers suggested sodium softeners or hardness-reducing typical cartridge systems. In practice, they turned out to be expensive to maintain, caused operational problems (including accelerated corrosion of the machine’s components), and their filtration capacity was sometimes unpredictable, with rapid scale accumulation and failures after depletion of the bed. Most significantly, the taste was still not satisfactory. So after about two-three years of testing, I designed my first proprietary reverse osmosis system: the water was first thoroughly purified, and then – with the help of a precisely set bypass – mixed in specific proportions with mains water. This was the first working version of my system, implemented in my own coffee shop. The effect in the cup convinced friends in the industry. After seeing the installation, they suggested building a solution specifically for food service establishments to provide them with stable, repeatable water quality for espresso and overflow methods. That’s how the journey began in a nutshell.

A.H.: Did you draw conclusions mainly based on the taste of the coffee, or did you study water parameters in parallel? How exactly did you go about this process?

P.S.: I was working on a reverse osmosis filter and bypass from mains water, so I wasn’t selectively changing the composition, but realistically adjusting the mineralization by dilution. I was looking for a mixing ratio that would give the best taste effect, while being safe for the equipment. At the same time, I took basic but systematic measurements: mineral content (TDS/conductivity), hardness, and pH – these are standard to assess the risk of scale and corrosion. I also gained a lot of practical knowledge from forums: aquarium, wine and brewing forums. I was struck by how lively the topic of water is out there and how competent home users are. I spent a lot of time on these forums, picking up specific tips and translating them into settings that work in the café so that the taste is reproducible and the water parameters stick to safe ranges.

A.H.: Since you came to this by trial and error at home, what are the implications of this in a broader context? Does it somehow “translate”, have implications?

P.S.: Yes. First of all, it is worth noting that when brewing coffee, there are recognized standards, clearly described ranges of water parameters in which coffee performs best. This has been verified many times: tests have been done, blind tests have been done, statistical tools and sensory evaluation have been used, so you know when the brew is on point. On the other hand, it becomes crucial to apply these assumptions to the reality of a coffee shop. I know the Polish gastronomy, so I knew from the beginning that it was necessary to develop a solution that takes up little space, is cheap to operate, economical in terms of water rejection, and most importantly, provides consistent mineralization in small volumes. Because getting repeatable parameters in a large vat, say at 1^m3, is relatively easy. We operate on a micro-scale: with pour-over coffee, we are talking about 1 liter, which must be the same every time. Similarly, with espresso, the water in the boiler mixes, but ultimately we are operating on small quantities, so maintaining stability is particularly challenging.

And here we come to the point: anyone involved in osmotic systems knows that the membrane works differently at the beginning of production (when the pressure behind the membrane is low) and differently when the pressure increases during operation. If you add a bypass, where the pressure is also not constant, you get additional variability: the water has a different level of mineralization at the start of the cycle and another at the end. For years I worked on how to tame this variability and build a system that keeps the mineralization at a constant level from the start, without floating parameters. And I succeeded, I have a stable solution that meets these assumptions in real conditions of the cafe.

A.H.: It is these implications that I wanted to talk about. In addition to having implemented the solution at your place, have you been able to apply it in other places? I’m asking because the water in the network sometimes varies – once it’s underground intakes, other times it’s surface intakes – the quality changes, the mineral profile too. How did you deal with this? I understand that you set the parameters for the baseline conditions at your location, but what about further – how did you translate this into implementations at other locations?

P.S.: It should be noted that mineralization by bypass is the simplest and most obvious solution. It works, but depending on the location the final water profile will be different. It may fall within the target ranges set by the SCA (Specialty Coffee Association), but differences will remain. And it’s good that you bring this up, because it pushed me a step further. There was the idea of a water standard that could be maintained regardless of location. It also came out of industry conversations: we ran a coffee shop, we had a roaster, I talked to employees at other places. When something in the taste wasn’t right, the water was often blamed, and sometimes rightly so. Except that once the water was put together, that argument fell away. That’s when I realized that even after using my system, after the bypass itself, the proportions of minerals in different locations would vary. So I came up with a rather bold idea: I would build a device that would dispense liquid mineral solutions into the water. That is, first we completely purify the water through osmotic membranes, and then precisely add specific minerals from the solution. That’s how the concept of a single, reproducible water standard that can be maintained regardless of source or location came about.

A.H.: Let’s go back to the question of cost and scale. It’s well known that at the end of the day, a lot of decisions and investments in cafes come crashing down on the budget. Is this an acceptable expense for a small café? And how widely have you been able to implement it? Are we talking about a few, a few dozen or already a few hundred locations in Europe?

P.S.: The specialty coffee shop segment is peculiar: on the one hand, it can generate higher margins than classic concepts, and on the other hand, it is often backed by the passion of people who will do a lot to make the coffee really taste good. Our solution today is one of two available in Europe in such a formula, so some venues, wanting to maintain repeatable quality, simply do not have a viable alternative. Price-wise, we compare favorably with the other supplier, but we don’t compete with it in terms of corporate scale; rather, we operate as a project tailor-made for coffee shops and hotels, which the market apparently accepts. As for numbers: we have different generations of devices (we just released the third), and the total is already close to two hundred active users. Most are in Poland, which is not surprising, since I originally built the system for my own café, and only then did we go out more widely.

A.H.: And the broader environmental context? There’s a lot of talk about the environmental footprint of a cup of coffee, about water and energy consumption throughout the chain. Does this topic realistically resonate in the industry, or is it sometimes put aside? And what are you guys doing about it in practice?

P.S.: We talk about this regularly, internally, with partners and with roasters, and we look for solutions that are achievable at our scale. We are not a big company, so some of the technology is simply out of our reach because of the high cost. However, we are doing what we can: working to lower our carbon footprint, choosing greener options where it makes operational sense. In the café itself, we recover water from the osmosis system, we collect the so-called “reject” and use it, for example, to cool the chillers or for washing. These are not spectacular volumes, but they add up to concrete. Frankly speaking, one of the real problems in Europe is still the low price of water for businesses. As long as water is cheap, few invest in recovery or closed-loop circuits, business-wise it often just doesn’t pay off. This was well illustrated in the example of energy: it was only the price spike that motivated many places, us included, to save money. After the wave of increases (still the aftermath of the pandemic), we managed to reduce power consumption by about 40 percent, optimizing procedures and equipment. We’re doing the same with water: step by step, within what the scale and economics of the café realistically allow.

Pawel Siemaszko, born in 1984, began his adventure with coffee in 2007, co-founding one of the first specialty coffee shops in Poland. In 2011 he founded the Kafo café in Gliwice, and since 2015 he has been co-founding the Kafar coffee roaster. The search for the best coffee water has been going on for 12 years.

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