A roaster’s guide to roller grinders

Josephine Walbank
May 16, 2022
A roaster's guide to roller grinders

For roasters, creating exceptional coffee is about more than sourcing high-quality green beans. 

Coffee beans need to be handled in a way that highlights their unique characteristics. This includes choosing the optimal roast profile, as well as grinding and brewing the beans with care and precision.

Grinding is one of the most pivotal yet underrated stages in a coffee’s journey from seed to cup. In particular, achieving grind consistency is vital, as grind size directly correlates to extraction rate.

To ensure consistency, roasters can choose to invest in roller grinders. In comparison to burr grinders, these machines can grind larger volumes of coffee by pushing the beans through pairs of corrugated rollers, producing a more uniform grind size.

Read on to learn more about what to consider before investing in roller grinders. 

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Caucasian hand holds unbleached kraft coffee pouch under roller grinder to collect ground coffee.

What is a roller grinder?

Roller grinders are a specialist type of equipment which grind coffee beans by passing them through a series of rotating steel cylinders. 

These cylinders work in pairs and rotate so their movement is directed at the centre of the machine. Coffee beans are fed through the top of the machine and pass through pairs of rotating grinders. 

The beans are forced through a gap between two cylinders, with the pressure of this movement breaking them down until they reach the required grind size. Each pair of grinders has a role and achieves a different ‌grind. 

Typically, roller grinders have at least two sets of cylinders, but some may have up to four. The first grinders act as pre-breakers, crushing the beans to achieve pieces around 1mm in size. 

Then, the second pair of grinders apply stress to make the ground beans even smaller. The amount of shear stress applied is the variable that shapes the grounds to the required size. 

Each cylinder in the second set of grinders will have corrugations across the surface. This refers to grooves that are cut into the metal at an angle, helping to cut the beans into the required size. 

While crushing is an effective way to reduce bean size, it does not achieve the evenness required for coffee grounds. 

To create the even and spherical finish, a shear cutting force is needed. This occurs when stress is applied to a material from opposite directions. To achieve this, two roller grinders move at different speeds relative to each other. Then, the sharp-edged corrugations “cut” the grounds into the desired size. 

Roasters can change the grind size by adjusting the gaps between the rollers. However, this can be more complicated than it sounds. 

Due to the staged nature of roller grinders, all the rollers need to be adjusted in accordance with each other. Furthermore, the distance needs to be considered across three different dimensions. 

Notably, these settings are so precise that roller grinders often have specialist control mechanisms that adjust the gap sizes with extreme accuracy. 

Medium roasted coffee beans in a coffee grinder with black background.

What are the benefits of roller grinders?

For roasters, achieving grind consistency is vital, as it directly correlates with extraction time. 

Finer grinds have a larger surface area and, in turn, a higher extraction rate. This often results in a stronger cup of coffee. 

If coffee grounds are uneven, they will extract at different rates. As a result, the coffee will not have the desired intensity and may be too strong or too weak. 

One of the major benefits of roller grinders is they grind coffee with a high level of precision – significantly more than cheaper alternatives, such as blade or conical burr grinders. This uniformity helps ensure hot water extracts all of the coffee’s soluble compounds evenly.

Another key benefit of roller grinders is they tend to operate at a lower temperature than other grinders. This preserves the coffee’s flavour by ensuring it is not accidentally “roasted” further. 

Finally, in blade and conical grinders, the mechanisms are exposed to air. While this is fine for domestic or small-scale use, it may compromise a roastery’s hygiene standards. 

By keeping the mechanism in a sealed unit, roller grinders are a more hygienic piece of equipment. This offers particular benefits to large-scale roasters, who will often need to grind vast quantities of coffee.

White V60 coffee brewer on scale with hot water being poured over fine coffee grounds.

What to consider before investing in a roller grinder

Roller grinders have a number of benefits for roasters, but there are factors to consider before making the investment. 

Primarily, roasters must consider the cost, as roller grinders are significantly more expensive than other types of grinders available

If a roastery is in its infancy, or roasters can fulfil orders using their current equipment, it may be better to wait before upgrading the equipment. 

The best time to invest in a roller grinder is when the roastery is well-established with a consistent customer base. Additionally, roasters who are struggling to meet demand or who have taken on a big contract with an organisation may find roller grinders beneficial.

When the time comes to invest in a roller grinder, roasters must choose a suitable model. Higher quality roller grinders will allow roasters to save specific grind settings needed for their coffee. This makes repeated grinding and switching between different product types infinitely easier. 

For instance, if a roaster grinds for filter and espresso, they require a roller grinder that not only grinds to both size types, but makes it easy to switch from one setting to another. 

Additionally, roasters should choose a roller grinder that comes with a maintenance service to ensure it continues working efficiently for as long as possible. 

In order to choose the best model, roasters will need to consider the equipment’s size, its ease of use, and the grind speed required. It is important to note that this is usually measured in kg/hour. 

These factors will depend on a roaster’s budget, the products and quantities they’re grinding for, and the space available. 

While whole bean is a popular choice for many, pre-ground is the most widely consumed form of coffee. As such, it’s important for roasters to invest in coffee grinders that not only provide a consistent grind, but also keep up with consumer demand.

Once the coffee is ground, the next step is to package it. Generally, pre-ground coffee loses its aromatic compounds significantly quicker than whole bean. Therefore, it is essential that roasters invest in high-barrier packaging fitted with degassing valves.

White V60 with filter paper sits on wooden counter beside white mug and white multilayer coffee pouch with dark roasted coffee beans on table.

At MTPak Coffee, we offer a range of sustainable coffee bags and recyclable degassing valves that will keep your pre-ground fresh, from roasting all the way to consumption.

Our range of kraft and rice paper, and polylactic acid (PLA) materials are all fully compostable and recyclable, while our low-density polyethylene (LDPE) packaging can be easily reused, or recycled.

You can tweak each packaging design to fit your needs, as well as including two or more layers to ensure maximum freshness.

For more information on sustainable coffee packaging, contact our team

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A roaster’s guide to roller grinders

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