Customized Roll Grinders for Coffee Capsules

By Dan Bolton

Grinding freshly roasted coffee for drip brewers is simple compared to the requirements for capsule production where identically sized particles pose problems. Consistent particle size is a primary consideration in drip applications but coffee in capsules must be consistently inconsistent.

This is known as bimodal particle distribution, a mix of uniform fines and larger particles that produces a stronger shot of espresso with more body.

During the grinding process, a single bean is crushed into 500-800 particles to make drip brew. Coffee for capsules is ground to a much finer 3,000-3,5000 particles, increasing its surface area from 3.5 to 100 cm2. Under a microscope, a bimodal grind will display like-sized particles grouped into fines and larger particles.

Since different sized particles saturate at different rates, leading to differences in the percentage of extraction, the ideal is to produce uniform groups of slightly irregular shaped particles. This is because coffee that is too finely ground and uniform compacts, slowing water flow that leads to over-extraction (greater than 20%) and a bitter cup. Uniform particles that are too large lead to channeling, where the water injected into the capsule fails to saturate grounds, leading to weak brew.

Neuhaus Neotec developed its three-stage WMS-E series grinders to prevent capsule channeling and over-extraction. The speed of each roller is independent allowing a “fast” and “slow” pairing. Combined with variable grinding pressure (roll against roasted bean) this highly dynamic system produces extremely uniform and reproducible particles at high throughput.

“Changing the gap and independently changing speed of the rotors is a key factor,” says Ralf Torenz, Neuhaus Neotec sales director. Making its roll grinders extremely flexible enables bimodal grinds at high speed and large volume.

There are many combinations in which facing rotors are sped up slightly on the left and slowed at right, Torenz explains. Corrugated rollers can be paired as sharp to sharp, or sharp-dull, dull-dull, or dull-sharp. Continuous speed regulation and grinding gap adjustment in three stages enables operators to develop a nearly infinite combination of settings that are programmed and easily reproduced, he says.

Precision grind

Packing coffee into 8-gram capsules requires precision, so much so that grinding for single-serve applications presents technical challenges addressed by Neuhaus Neotec in its next-generation Neogrind series machines.

Since production runs are long, operators must concern themselves with machine efficiencies such as cooling rotors to prevent variations in gap. Temperature also affects the coffee. Cooler coffee is more brittle which causes more fines to be produced during grinding. Coffee at higher temperatures is malleable, reducing the number of fines and increasing flow rate.

“Uniform particle distribution, even in the finest grinds, as well as a high reproducibility and low-dust grinding are the strong points of these machines,” according to Neotec’s Michael Ziemann, an engineer who helped develop the dual-speed rollers and reduction gear design.

“The aim was not only to comply with legal standards for energy-efficient motors but to exceed them. With the IE-3 motors for the optional individually driven, continuously adjustable rolls, Neogrind relies on particularly energy-efficient motors assuring a high capacity,” he said.

Ziemann explained that temperature controls ensure the temperature of each roll can be maintained (which requires heating rolls at the beginning of the run and cooling as the run progresses). A smooth-walled grinding chamber prevents product adhesions and the grinding chamber is fully accessible in order to facilitate cleaning. Like the other grinders of the Neuhaus Neotec grinder family, the Neogrind can be easily customized thanks to different configuration options.

Capacity varies with the roller length. A 200 mm roller produces 200 kilos per hour (espresso settings) and 650 kilos per hour at filter coffee settings. A 400 mm roller produces 400 kilos per hour of espresso grind and up to 1,300 kilos per hour of filter grind.

The Neogrind is specifically designed for coffee capsules and pods and offers the highest accuracy in particle distribution, closing a gap in the company’s family of grinders that span a range from laboratory to full-scale commercial grinders.

Learn more: www.neuhaus-neotec.de/en/neuhaus-neotec-coffee/products/grinders/