I've recently been asked this question by a few patients so I thought it would make a good topic for this month.
Decaffeination can be done via a few different processes, some safer than others, and they also have different impacts on flavour.
To be clear, decaf does NOT mean caffeine free - in tea, approx 1-2% of the caffeine remains, in coffee, about 2-4% of caffeine remains (or 2-5 mg compared to 50-75mg in regular coffee).
The 3 main processes to decaffeinate are:
1. Water processing - this employs a charcoal filter which absorbs the caffeine. This charcoal has been pre-treated with a carbohydrate, typically sucrose, that helps it absorb the caffeine without removing other compounds that contribute to the flavour of the tea/coffee. It removes 94-96% of the caffeine.
2. Direct solvent method - this technique typically employs methylene chloride (or dichloromethane) or ethyl acetate. Methylene chloride is considered a toxin and has been shown to be carcinogenic (cancer causing) in animal studies. Companies that use this solvent claim that most of it is removed at the end of the process, leaving insignificant levels on the roasted coffee or tea leaves. However, the amount of solvent remaining, and the degree to which it poses a health risk, is a matter of dispute. It removes 96-97% of the caffeine.
Ethyl acetate is an ester that is found naturally in fruits and vegetables such as bananas, apples, and coffee. It is considered safe and non-toxic, but it tends to remove more flavour from tea than other processes.
3. CO2 - this method involves using carbon dioxide which is completely non-toxic. It is good at preserving flavour, but it is an expensive process. The CO2 is recycled for further use, which is also a plus. It can extract 96-98% of the caffeine originally present in coffee beans.
I don't generally recommend brands or products, but you can assume that if the company don't mention on the packaging or their website that the product is decaffeinated with water or CO2, then it's likely a solvent, either ethyl acetate, which is acceptable from a health perspective, or methylene chloride, which I have reservations about in terms of potential toxicity.
Enjoy your cuppa!