Analyser wakes up and smells the coffee

Edited by the Engineeringtalk editorial team Jan 27, 2005

Douwe Egberts is using a Servomex 574 portable gas analyser for each packaging line for its novel Senseo coffee pods.

A revolution in coffee is spreading around the world, thanks to the Senseo brewing system developed jointly by coffee company Douwe Egberts and electrical appliance manufacturer Philips.

One of the keys to its success is that within 1 minute it brews up to two cups coffee that taste as if they are made with freshly ground real coffee, but without any mess or hassle.

To ensure the unique coffee pods - which look similar to round tea bags - stay fresh in their outer packaging, Douwe Egberts is using a Servomex 574 portable gas analyser for each packaging line.

Roasted and ground coffee quickly loses its freshness if exposed to oxygen, so Douwe Egberts packages the coffee pods in sealed foil bags using nitrogen.

To ensure this vital process is being performed correctly sample packs are tested every hour.

There are packaging lines for the different blends of coffee and each has its own Servomex 574 portable oxygen analyser.

To perform a test the operator pierces the sample pack with a probe that consists of a hypodermic needle, the tip of which is surrounded by a foam pad to prevent the ingress of gases from the working environment.

A small volume of gas is then extracted by the analyser's internal pump (an inline filter ensures only gases are drawn into the measurement cell), and the result is shown on the display in a matter of seconds.

Douwe Egberts already had experience of the paramagnetic technology used by Servomex in its oxygen analysers, having employed Servomex instruments in other packaging plants, so it had no hesitation in ordering four units for the first four packaging lines, then more as other lines were brought on stream to cope with soaring demand.

Paramagnetic sensing technology is the only feasible option for analysing oxygen in roasted coffee applications.

The reason for this is that roasting coffee produces a small amount of carbon monoxide that is absorbed by the coffee.

This slowly outgasses and can lead to false negative readings on oxygen analysers that use high-temperature catalysts such as zirconia: if the gas sample is heated to 700C, the combustible carbon monoxide reacts with any oxygen present to form carbon dioxide.

Because the oxygen is consumed in this way, catalyst-based oxygen analysers tend to give a low or zero reading.

The Servomex 574 paramagnetic oxygen analyser, however, operates at ambient temperatures, so there is no opportunity for oxygen to combine with carbon monoxide.

Readings are therefore utterly reliable.

Furthermore, the nondepleting paramagnetic technology in the sensing cell enables operators to be certain that the analyser will always function correctly; in contrast, other sensing technologies can degrade, giving no indication that the readings are misleading.

Douwe Egberts has purchased one Servomex 574 for each packaging line, despite the fact that the instruments are portable.

Nevertheless, the small size and portability are beneficial because of the limited space available in the area around the packaging line and the ease with which the instruments can be carried back to a quality assurance (QA) laboratory for recalibration if required - though the Servomex 574 can be readily recalibrated in the production environment using nitrogen and/or air to maintain its accuracy of 0.2% oxygen with a repeatability of +/-0.1% oxygen.

In a QA application where several packs have to be tested in a short period, ease of use and speed of response are extremely important.

The Servomex 574 scores highly in both respects, plus it has an analogue output that can automatically feed data to a QA system for storage and analysis if required.