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

Coffee capsules are here to stay. For many, it's the most convenient way to drink coffee. Others see too many compromises: in terms of taste and, above all, ecologically. In his guest article, Patrizio Frigeri explains what capsules can and can't do, and how ecologically sound capsule coffee is.

A guest article by Patrizio Frigeri*

What can capsules do really well?

They guarantee easy preparation using pre-portioned coffee in conjunction with the appropriate machine.

The criticism of capsules, regarding what they can't do, often goes like this: Capsules don't make proper espresso. They're expensive compared to bean coffee and only produce waste.

Let us 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 knows the success story by now. I recommend watching the DOK program on Swiss television; starting at minute 32, you'll be taken directly to Eric Favre's contribution .

But Nespresso is no longer the only provider – Nespresso clones and proprietary systems can be found everywhere. Due to the complex production process, it was primarily large companies that offered capsules in their product range in the past. However, two things are currently changing : more and more small roasters are offering their coffee in capsules, and there are signs that specialty roasters are also no longer averse to coffee capsules.

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

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

Patrizio Frigeri

Saeco already had this ambition when it invented the fully automatic coffee machine. When people began making espresso at home, resourceful engineers came along and wanted to simplify the grinding and extraction processes for the consumer.

The capsule system goes one step further than fully automatic coffee machines, relieving the consumer of the grinding task , thus solving several problems: first, there's no stale coffee due to packages being opened too long, and second, it eliminates the need to adjust the optimal grind size. This is already determined by the capsule filler.

The grind setting on fully automatic coffee machines isn't always ideal depending on the bean variety, and the adjustment options are usually limited to a few levels. The capsule arrives perfectly sealed in an airtight container, "freshly roasted."

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

Green coffee & roasting of coffee capsules

Similar to other coffee products, capsules can be used in single-origin coffee or as a blend. The coffee is generally roasted a bit darker than for a portafilter machine , because the extraction time with a capsule is short, and as much coffee as possible should be extracted from the grounds in this time.

Filling and packaging of coffee capsules

After roasting, the coffee is allowed to settle for a while to release gases. The beans are then filled into capsules under oxygen-free conditions. The fill weight is usually between 5 and 6 grams. After filling, the capsule is sealed with a foil seal.

Delivery

The capsule coffee arrives pre-packaged in a carton containing 10 to 20 capsules. Some capsules are also packaged in a so-called single-flow pack . This often indicates that the capsule itself is not airtight, and a protective plastic sleeve is intended to compensate for this.

As a consumer, you should avoid such capsules in order to generate unnecessary packaging material and to ensure that you receive a good quality cup of coffee with the necessary “freshness”.

The capsules in the machine

Ideally, the consumer places the capsule in the coffee machine as soon as possible. This usually requires turning on by pressing a button. The heating time of the heater (thermoblock) is typically no more than 30 seconds.

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

Preparation 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 piercing systems vary . Some pierce only the pump side first, while others, for patent reasons, also lightly pierce the outlet side.

A distinction is also made between whether the piercer is pierced with one or more so-called needles. Each development has its own background as to how the piercer is pierced. In most cases, people were convinced that a certain arrangement of needles and capsule shape would produce the best capsule coffee in the cup.

Extraction of the coffee capsules

At the touch of a button, you can now start the extraction. There are different systems here, too, but most allow the user to choose between a short or long cup, or between different volumes (Dolce Gusto).

Extraction in progress

The extraction process begins, the water flows into the capsule, and the coffee is pre-brewed. As soon as sufficient pressure is built up in the capsule, the foil at the bottom of the capsule bursts, and the coffee flows into the cup.

Here some customers often ask themselves:

Why does capsule coffee produce so much crema? It's primarily due to the carbon dioxide ( _CO2 ) still present in the coffee from the roasting process, which has nowhere to go—it remains in high concentrations in the capsule. Similar to ground coffee, the fresher the coffee, the more crema you get in your cup. Additionally, during extraction, turbulent currents around the pierced foil promote crema formation.

Capsule ejection

To eject the capsule, you open the brewing chamber, which releases the capsule and ejects it into a container. There are also systems on the market where you remove the capsule holder and eject the capsule separately outside the machine.

Waste

The machine's container is emptied after about six uses. The capsule then goes into the incinerable waste bin or, more recently, into the green waste bin.

Capsule coffee – a separate beverage category

In popular parlance, especially in Switzerland, one receives a "Nespresso." For many, the coffee is simply called that because "Nespresso" has now become the name for a distinct preparation category: the category of coffee preparation using pre-portioned coffee in a capsule.

If you consider this as a category, you won’t be tempted to compare the “Nespresso” with a drink made from a portafilter.

It makes sense to compare capsules with capsules. Just as there are significant differences between espressos from portafilter machines, the quality of capsule coffee varies enormously. Some roasters invest their energy in capsule technology, neglecting quality coffee. Others, on the other hand, aren't yet able to offer flawless technology, but strive to bring complex flavor to the capsule.

Back to the point of what ends up in the cup as extraction. Of the 5g of coffee in the capsule, you get 4% of dissolved solids in the extracted liquid of around 25 grams in a regular short coffee. This results in an extraction of exactly 20%, the desired level in the coffee world. However, the default setting for most capsule machines is at least 40ml per cup, which then dilutes the beverage. However, each user can determine the amounts, or rather the volume of the beverage, themselves. In this case, it's worth keeping the extraction shorter.

The aromas and flavors vary depending on the bean variety and roast level. They range from floral, berry, and acidic notes of a single-origin Ethiopian from the market leader to chocolatey, nutty, and sweet notes 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 by Nestlé
• Nescafé Dolce Gusto from Nestlé
• Cafissimo from Tchibo
• Delizio or Cremesso from Delica
• Tassimo by Jacobs Douwe Egberts

As already mentioned, the systems differ not only in the capsule shape but also primarily in how, where, and when the capsule is pierced . The machine itself usually uses the usual components to produce the coffee in the cup, these are:

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

The free flow of coffee from the capsule directly into the cup is a major advantage with Dolce Gusto. With Dolce Gusto, the coffee spout is integrated into the capsule, so no components come into contact with the coffee, making cleaning extremely easy. Cleaning is a good keyword:

With the capsule system, users feel like they can only "consume." This isn't the case, as most capsule machine brewing units can become rancid due to poor cleaning.

Patrizio Frigeri

With a suitable cleaning agent (e.g. cleaning capsule), the coffee fat can also be removed from the parts containing coffee extract before they become rancid.

What are the capsule bodies and closure foils made of?

The materials are usually aluminum, plastic, or a composite of plastic and aluminum . These materials have also proven effective for storing beans in bags. They provide a high level of protection for the roasted and ground coffee. This protection is important to prevent oxygen from penetrating the coffee, which would otherwise begin to degrade and lose quality.

Of course, it would be better if no packaging were involved at all. In the luxury food sector, where high quality is valued, precious items must be protected from spoilage using appropriate means. However, great progress has been made in the area of ​​biodegradability of materials.

There are now several capsule bodies that offer biodegradable properties combined with a high oxygen barrier to protect the coffee. Biodegradable materials come in two grades regarding compostability.

Industrial compost

Group 1, mostly polymers based on lactic acid or sugar cane, are materials that can be used for industrial composting, e.g. for the production of biogas.

Home compost

Group 2 consists of materials that can be added to your own compost heap (plant-based polymers). The lids of most compostable capsules are made of a special, multi-layered paper.

Capsule coffee waste and ecological footprint

How large is the ecological footprint of coffee capsules? In short, the issue is more complex than simply focusing on the packaging. A life cycle analysis (LCA) can be very helpful here. The Quantis laboratory, for example, conducted one comparing capsule coffee with espresso made with a portafilter and filter coffee.

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

It is clear that more packaging material is needed per gram of coffee with the capsule, namely 0.2 grams per gram of coffee , i.e. 2.5x more than with bean coffee.

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

It's also noticeable that usage accounts for the second largest share. To specifically influence the grams of _CO2 -eq. as a consumer, you have to start with usage or preparation. Furthermore, the coffee packaging can be optimized. Here, it's important to avoid resource-intensive materials like aluminum.

Portafilters are more “environmentally harmful” than capsule machines in terms of use.

According to the graph above, a batch-brewed coffee that is kept warm on a plate for 2 hours performs by far the worst in the gCO ₂ equivalence analysis.

Those who brew filter coffee precisely and without loss perform best.

I would now like to briefly explain the preparation in more detail using the example of filter coffee (manual preparation), a capsule machine (Nespresso) and a portafilter (Rocket Appartamento).

The following assumptions were made for the following table:

• Filter coffee: A person enjoys a coffee twice a day, prepared with 15g of coffee and 250g of boiling water
• A kettle for this example has an 1800W power rating and a maximum capacity of 0.8L. It takes 115 seconds to boil 0.5L of water.
• The ideal situation when preparing filter coffee would be to boil exactly 250g of water and not use hot water to rinse the paper and heat the containers.
• The standard procedure for filter coffee, however, involves rinsing the paper before extraction and heating the containers . Assuming 400g of water.
• For the Nespresso and portafilter machines, the annual consumption stated on the energy label was used. The laboratories that determine this consumption follow a protocol that reflects the normal use of the machine and makes it comparable with other appliances.

Consideration in form of kg CO ₂ -eq.
(annual consumption multiplied by electricity mix value)

What stands out?

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

Portafilters perform poorly because a cup of coffee requires a lot of energy. At best, you heat 0.5 liters of water, and at worst, 1.5 liters (on the largest home portafilter machine) to produce 20 grams of coffee extract.

To give everyone an idea: the annual consumption of a portafilter machine is roughly the same as driving 1,000km in a car.

Here's a brief comparison of the ratio of ground coffee to the resulting coffee liquor. Knowing that coffee production is the biggest driver of the ecological footprint, consumers have control over how much and which type of coffee they use. The higher the ratio, the more liquid they get from the coffee used.

Why does the capsule system perform so well?

You extract a good cup of coffee without wasting ground coffee and without unnecessary energy consumption (minimal use of resources) .

This is just a brief glimpse into the world of life cycle assessments in the coffee industry, specifically capsules. Detailed studies can be found online if you want to delve deeper into the topic. However, this brief overview should suffice to enable future discussions regarding the life cycle assessment and waste of coffee capsules to be approached in a more nuanced and objective manner.

Our own measurements

We've been doing a lot of measurements ourselves over the past few months. Tobi captured the findings in his graphs, which we published in a post in January 2024.