How do coffee capsules work? Everything about the system, taste, and criticism of single-serve coffees

Capsule coffee is here to stay. For many, it is the most convenient way to drink coffee. Others see too many compromises: in taste and, above all, ecologically. In his guest article, Patrizio Frigeri explains what capsules can and cannot do, and how ecologically sensible capsule coffee is.

A guest article by Patrizio Frigeri*

What can capsules do really well?

They guarantee easy preparation of pre-portioned coffee in combination with the appropriate machine.

Criticism of capsules, what they can't do, often sounds like this: capsules don't make real espresso. They are expensive compared to bean coffee and only produce waste.

Let's classify these positions.

The capsule was invented more than 40 years ago by Nestlé engineer Eric Favre and successfully marketed by the same company. Everyone now knows its success story. I recommend the DOK broadcast from Swiss television, from minute 32 it goes directly to Eric Favre's contribution.

However, Nespresso has long ceased to be the only provider - Nespresso clones and proprietary systems can be found everywhere. Due to the elaborate production, in the past it was mainly large providers who had capsules in their product range. However, two things are currently changing here - more and more small roasters are offering their coffee in capsules, and there are signs that even specialty roasters are no longer averse to coffee capsules.

What makes the coffee capsule system so successful? Freshness, grind, simplicity, reproducibility

The capsule system is probably so successful because it allows all coffee lovers to extract a consistent cup quality at the touch of a button in an intuitive way, and this without any prior knowledge of coffee preparation.

Patrizio Frigeri

SAECO already had this claim when the automatic coffee machine was invented. When people started preparing espresso at home, ingenious engineers came along and wanted to simplify the processes of grinding and extracting for the consumer.

The capsule system goes one step further than the automatic machine, namely, it takes over the grinding from the consumer and thus solves several problems: firstly, there is no stale coffee due to packaging that has been open for too long, and secondly, the adjustment of the optimal grind size is no longer necessary. This is already determined by the capsule filler.

The grind size in automatic machines is not always ideal depending on the type of bean, and the adjustability is usually limited to a few settings. The capsule arrives perfectly sealed in an airtight container, "freshly roasted" to the customer.

Below, I describe the sequence of steps in the life of a capsule, from green coffee to waste.

Green coffee & roasting of coffee capsules

For capsules, as with other coffee products, the coffee can be single-origin or a blend. The coffee is generally roasted a little darker than for a portafilter machine, because the extraction with the capsule is short, and as much coffee as possible should be dissolved from the grounds during this time.

Filling and packaging of coffee capsules

After roasting, the coffee is allowed to rest for degassing. Then the beans are filled into capsules under exclusion of oxygen. The filling weight is usually between 5 and 6 grams. After filling, the capsule is sealed with a film.

Delivery

The capsule coffee comes pre-packaged in an outer box of 10 to 20 capsules to the consumer. Some capsules are still wrapped in a so-called single flow pack. This often indicates that the capsule itself is not airtight and a plastic protective cover is intended to compensate for this.

As a consumer, such capsules should be avoided in order to prevent unnecessary packaging material and to ensure that a good quality cup of coffee with the necessary "freshness" is obtained.

The capsules In the machine

For the consumer, the capsule ideally goes into the coffee machine as soon as possible. This usually has to be switched on by pressing a button. The heating time of the heater (thermoblock) is normally no more than 30 seconds.

Future technologies will no longer require heating aluminum, so-called mass-free heaters (known as instant heaters).

Preparation for extraction

When the capsule is inserted into the brewing chamber, the chamber usually has to be closed with a lever. When closing the brewing chamber, the capsule is pierced, but the systems differ in how they pierce it. Some pierce only on the pump side first, others, for patent reasons, also lightly pierce on the spout side.

A distinction is also made as to whether one or more so-called needles are used to pierce. Each development has its own background on how the piercing is done. Most of the time, a certain arrangement of needles and capsule shape was believed to result in the best capsule coffee in the cup.

Extraction of coffee capsules

Extraction can now be started at the touch of a button. Here too, there are different systems, but usually the user can choose between a short or long cup or between different volumes (Dolce-Gusto).

Extraction in progress

Extraction starts, water flows into the capsule and pre-brews the coffee. As soon as enough pressure builds up in the capsule, the foil at the bottom of the capsule bursts in a targeted manner and the coffee flows into the cup.

Here, some customers often ask themselves:

Why does capsule coffee produce so much crema? Mainly due to the carbon dioxide (CO₂) that is still present in the coffee from the roasting process and has nowhere to go – it remains in high concentration in the capsule. Analogous to bean coffee, the fresher the coffee, the more crema you get in the cup. In addition, there are turbulent flows during extraction around the pierced foil, which support crema formation.

Capsule ejection

To eject the capsule, the brewing chamber is opened, which releases the capsule and ejects it into a container. There are also systems on the market where the capsule holder is removed and the capsule is ejected separately outside the machine.

Waste

The machine's container is emptied after about six uses. Now the capsule goes into the combustible waste or, increasingly, into the organic waste bin.

Capsule coffee – a category of beverage all its own

Colloquially, especially in Switzerland, one gets a "Nespresso". For many, the coffee is simply called that because by now "Nespresso" indeed stands for its own preparation category, the category of preparing coffee with pre-portioned coffee in a capsule.

If one considers this as a category, then one is not tempted to compare (or have to compare) the "Nespresso" with a beverage from a portafilter.

It makes sense to compare capsules with capsules. Just as there are significant differences in espresso from a portafilter machine, the quality of capsule coffee varies enormously. There are roasters who invest their energy in capsule technology, neglecting quality coffee in the process. Others, however, cannot yet offer flawless technology but try to bring complex flavors into the capsule.

Back to the point of what comes into the cup as extraction. From the 5g of coffee in the capsule, you get 4% dissolved solids in the extracted liquid of about 25 grams for a regular short coffee. This results in an extraction of exactly 20%, the target value in the coffee world. However, the default setting on most capsule machines is at least 40ml per cup, which then dilutes the beverage again. However, all users can determine the quantities, or the volume of the beverage, themselves. Here it is worthwhile to keep the extraction shorter.

Aromas and taste vary depending on the bean type and roast level. From floral, berry, and acidic of a single-origin Ethiopian from the market leader, to chocolatey, nutty, and sweet of an Arabica blend from a small Zurich roastery.

Which capsule systems are available on the market?

The most important ones in Europe are as follows:

• Nespresso from Nestlé
• Nescafé Dolce Gusto from Nestlé
• Cafissimo from Tchibo
• Delizio or Cremesso from Delica
• Tassimo from Jacobs Douwe Egberts

As already mentioned, the systems differ not only in capsule shape but primarily in how, where, and when the capsule is pierced. In the machine itself, the usual components typically contribute to the result in the cup; these are:

• Heater with heating control for a defined brewing temperature
• Flow meter for monitoring the pumped water volume
• Vibratory pump for pumping water under pressure from the tank to the coffee capsule.

The free coffee flow from the capsule directly into the cup of Dolce-Gusto is a great advantage. With Dolce-Gusto, the coffee spout is integrated into the capsule, so no components come into contact with coffee, which simplifies cleaning immensely. Cleaning is a good keyword:

With the capsule system, users have the feeling that they can only "consume". This is not the case, as most brewing units of capsule machines can become rancid due to poor cleaning.

Patrizio Frigeri

However, with a suitable cleaning agent (e.g. a cleaning capsule), coffee oils can be removed from the coffee extract-carrying parts before they become rancid.

What are the capsule bodies and sealing foils made of?

The materials are usually aluminum, plastic, or a composite of plastic and aluminum. These materials have also proven effective in storing beans in bags. They provide high protection for the roasted and ground coffee. Protection is important so that no oxygen can reach the coffee, preventing it from deteriorating and losing quality.

Of course, it would be better if no packaging were involved at all. In the area of luxury foods, where high qualities are valued, the precious commodity must be protected from spoilage by suitable means. However, great progress has been made in the area of biodegradability of materials.

Meanwhile, there are several capsule bodies that offer biodegradable properties coupled with a high oxygen barrier to protect the coffee. For biodegradable materials, there are two qualities regarding the possibility of composting.

Industrial compost

Group 1, mostly polymers based on lactic acid or sugarcane, are materials that can be fed into industrial composting, e.g., for biogas production.

Home compost

Group 2 materials are those that can be added to one's own compost heap (plant-based polymers). In most compostable capsules, the lids are made of a special, multi-layered paper.

Capsule coffee waste and ecological footprint

How high is the ecological footprint of coffee capsules? In short: the issue is more complex than simply reducing it to packaging. A Life Cycle Assessment (LCA) helps a lot here. The Quantis laboratory, for example, conducted one that compares capsule coffee with portafilter espresso and filter coffee.

The capsule as a packaging unit itself performs poorly compared to other forms of coffee presentation. However, to assess the capsule and its ecological footprint more objectively, the origin of the coffee and the preparation method at home must be included in the consideration.

It is clear that per gram of coffee, the capsule requires more packaging material, namely 0.2 grams per gram of coffee, which is 2.5 times more than for bean coffee.

However, if we look at the entire chain, a different picture emerges. The following graph from the Quantis report provides the following insight:

Furthermore, it is striking that usage accounts for the second largest share. To specifically influence the grams of CO₂-eq. as a consumer, one must start with usage, or rather, preparation. Furthermore, the coffee packaging can be optimized. Here it is important to avoid resource-intensive materials such as aluminum.

Portafilter machines are "more harmful to the environment" than capsule machines in terms of use.

According to the graph above, batch brew coffee kept warm on a hot plate for 2 hours performs the worst by far in terms of gCO₂ equivalent.

Those who brew filter coffee very precisely, without waste, perform the best.

I would now like to explain the preparation in a little more detail using the examples of filter coffee (manual preparation), capsule machine (Nespresso), and an espresso machine (Rocket Appartamento).

The following assumptions were made for the table below:

• Filter coffee: One person enjoys coffee twice a day, prepared with 15g of coffee and 250g of boiling water.
• A kettle for the purpose of this analysis has 1800W and a maximum filling volume of 0.8L. It takes 115 seconds for 0.5L of water to boil.
• The ideal case for preparing filter coffee would be to boil exactly 250g of water and not use hot water to rinse the paper and preheat the vessels.
• The normal case for filter coffee, however, is preparation with rinsing the paper before extraction and preheating the vessels. Assumption: Heating 400g of water.
• For the analysis of Nespresso machines and espresso machines, the annual consumption mentioned on the energy label was used. The laboratories that determine this consumption follow a protocol that represents the normal use of the device and makes it comparable with other devices.

Analysis in terms of kg CO₂-eq.
(annual consumption multiplied by electricity mix value)

What stands out?

Preparing a cup of coffee with a capsule machine is quite efficient. If you consider over-preparation with filter coffee (heating too much water, brewing too much coffee, grinding too much coffee, preparing more coffee), the annual consumption increases rapidly.

Espresso machines perform poorly because a lot of energy is simply needed for one cup of coffee. In the best case, 0.5 liters of water are heated, and in the worst case, 1.5 liters (largest home espresso machine) to then obtain 20 grams of coffee extract.

To put it into perspective: the annual consumption of an espresso machine is roughly equivalent to driving 1,000 km in a car.

Here is a brief comparison of the ratio of ground coffee to the resulting liquid coffee. Knowing that coffee production is the biggest driver in the life cycle assessment, consumers have control over how much coffee and what type of coffee they use for their preparation. The higher the ratio, the more liquid you get with the coffee used.

Why does the capsule system perform so well?

It extracts a good cup of coffee without wasting ground coffee and without unnecessary energy consumption (minimal resource input).

This is just a small insight into the world of life cycle assessments in the context of coffee, specifically capsules. Detailed studies can be found online if you want to delve deeper into the topic. However, this brief insight should be sufficient to approach future discussions regarding the ecological balance & waste of coffee capsules in a more differentiated and factual manner.

Our own measurements

We have done a lot of our own measurements in recent months. Tobi recorded the findings in his graphics, which we published in a post in January 2024.