Coffee machine

Question

Dear expert team,
how is it with coffee machines, that have a water tank, e.g. Senseo, Dolce Gusto...?
Is the coffee in spite of heating contaminated with bacteria, e.g. Pseudomonas or is it drinkable without problems for patients with CF? We have such a machine in the company and sometimes the water stays for several hours and I have worries if I could get infected with it.
Many greetings

Answer

Hello,
Heating leads to killing of the microorganisms. How effective microorganisms are killed by heat (water, steam, hot air), depends on the duration and the temperature but also on the number and type of the germs.

"Which type of germs" what does it mean?: P. aeruginosa belongs as many other humid-germs to the vegetative bacteria, that means it is not especially resistant to heat and can be killed rather easily by heat.

"How many germs" what does that mean? The higher the load with germs the longer it takes until there are no germs detectable any more due to heating. Drinking water, that is taken for preparing the coffee, is not free of germs, should however in general show only a relatively small load with germs and in Germany should also be free of Pseudmonas aeruginosa. A probelm could be, that subsequently a multiplication of germs takes place and the load of germs increases, if water will be stored a longer time. As driniking water is very poor in nutrients however, it does normally not come to a relevant multiplication of germs within a few hours at room temperature.

"Level and duration of temperature" what does this mean? Boiling of water (more than 93 degrees celius) for a short time e.g. 1 minute is sufficient, in order to kill vegetative bacteria in the water. In case the water temperature is reduced, the necessary time is getting higher, in order to achieve the same effect. The statements for water temperature and exposure time for killing effectively vegetative bacteria such as P. aeruginosa, fluctuate partly and are about 70°C/5 minutes or 71°C/3min. The today used coffee machines like Senseo, Dolce Gusto etc., are in general so concipated, that the water is not brought to boil, but only to temperatures around 90°C (86°C-92°C, dependend on the company) and therefore achieve the necessary temperatures of over 70°C for killing of vegetative bacteria.

Therefore the risk of getting a colonization or even an infection with P. aeruginosa via the consumation of so-prepared coffee is vanishingly small, if not even can be excluded totally. General hygienic measures, like letting run some water from the tap and take the next portion of water for the preparation, regular cleaning and decalcification of the machines, as well as to renew the water in the tanks preferably daily, helps to avoid unnecessary contamination with germs.
Yours sincerely,
Dr. Michael Hogardt

05.11.2009