Ethanoic acid http://www.p4c.philips.com/cgi-bin/dcbint/cpindex.pl?scy=ZA&slg=ENG&ctn=HD5405/60&dct=FAQ&refnr=0092154&view=aa12_view_partial.html&session=20120502004843_66.249.71.242&faqview=1 We advise you not to use acetic acid-based descaler (vinegar), as this could have a negative effect on the taste of the coffee.
Note: Never use an acid- or vinegar-based descaling agent with 8% or more acetic acid to descale the appliance, as this may cause damage. http://www.diynot.com/forums/viewtopic.php?t=30088#axzz2Bph0xR9a Citric acid will do a better job than the acetic acid in vinegar. That's because calcium citrate dissolves in water whereas calcium acetate forms an insoluble layer between the scale and the vinegar. You can buy citric acid crystals from home brew shops. A teaspoon of acid in a kettle of water is a good start and you can speed things up enormously by boiling the kettle - but watch out for fizzing! If it stops fizzing while scale still remains you have exhausted the acid. Simply add more.
http://scottiestech.info/2009/04/22/descaling-appliances-which-acid-is-best/
The type of acid you should use depends on the appliance, the severity of the mineral deposits, and the materials from which the appliance is constructed.
For example, people generally clean coffee makers by brewing a nice fresh pot of vinegar. Vinegar contains acetic acid, which is a fairly weak organic acid. Nevertheless, sometimes acetic acid is enough.
In other cases, you may want to purchase a commercial iron/coffee maker descaling product. Normally, this type of product comes in liquid or crystalline form. The key ingredient is usually sulfamic acid, an organic acid that is used for all kinds of interesting things. Sulfamic acid is an excellent descaling agent, and it is much safer for various types of metals. When strong enough, it will even remove rust (try it!).
Sulfamic acid is, in fact, my acid of choice for most applications. When it comes to sulfamic