The plasticizers in ordinary polypropylene and high impact polystyrene appliance parts (the most common plastics used in kettles coffee makers etc. ) do not leach out in normal use in concentrations you could taste. Could be the inventive and cost conscious moulders of appliance parts have changed to a different type of resin or are adding recycled unknown polymers , or may be using petrochemical mould release agents which create odd tastes. The petrochemical mould releases are cheaper than food grade vegetable oil based ones, but the petrochem ones should never be used for parts that have food or skin contact.
The more likely culprit (IF it is a plastic part to blame – see below) based on my experience with plastics moulding for appliances is the thermoplastic elastomers or vulcanizates (TPE or TPV) basically plastic rubber used for any seals or piping in the appliance. Some of these have additives that are very harsh smelling and these may be leaching into the water. EPDM rubber makes excellent seals but can smell bad really strongly, and can flavour water with the same bad smell.
Most coffee makers use a die cast metal heater housing / hot plate to heat the water. Water being heated is in direct contact with the metal. The metal is usually a corrosion resistant zinc aluminum alloy. If the wrong alloy is used, gases can be produced during boiling and sometimes sulfur or ammonia smells can result. I experienced this working with similar boilers from cappucino machines, that a firm I worked for were using for dental autoclaves.
I would not worry about BPA (bisphenol A) in moulded plastics. It was a very popular additive in polycarbonate until the 1990's when US media got on the bandwagon about it and pressured the food container industry to discontinue using it. The studies the media quoted were flawed and incomplete, and referenced found cancers in lab animals tested with hundreds of thousands of times higher levels of BPA in solution than you could ever leach out of a PC water bottle for example. If you change the water every day in a bottle or appliance, almost no BPA or plasticizer will ever leach out. This has been tested and verified by SPI-SPE in the US, as well as the USDA, but public opinion of it as a threat to health persists.
On the other hand the public is perfectly comfortable riding in a car for hours on a weekday commute, or to the beach on a weekend, passing through the exhaust of thousands of other petrol-burning cars and diesel burning trucks spewing many litres per minute of God knows what mix of burned and unburned hydrocarbons, oxides of nitrogen, oil vapour , decomposed MMA, benzols, ketones from ethanol burning, etc. I believe in time that vehicle exhaust exposure will be found to be a primary trigger in many types of cancers. It is far more dangerous than any plastic part found in your home appliances in my opinion.
If glass kettles can still be found, glass will have the least possible effect on taste and chemical residue in heated water for tea or coffee. Stainless steel a close second. Emptying and filling ANY kettle or container with fresh water every time will reduce the chance of leaching anything bad into the liquid, for any material.
Just my $0.02 worth. Standing by for the usual naysayers, malcontents and troll type activity.
Edited By Jeff Dayman on 13/02/2019 21:19:23