Coffee. The sacred bean. The sound of the grinder. The holy dark brown liquid. The warm feeling in the hands. The delicate smoothness of the foam. The slightly bitter aftertaste. The illusion of instant neuronal firing.
I started to drink coffee quite late in my life, less than a decade ago. As a teenager I felt way too immature for it. It is like red wine, tonic water, grapefruit, whisky and a medium-rare Sirloin steak – you first need to reach some kind of adulthood to enjoy it to its best. One of my (absolutely guiltless) pleasures on a sunny Saturday is to sit outside with a cup of black Robusta and observe for hours random people on the streets.
Robusta? Are we still talking about coffee or did you already move to another topic?
Let’s start with the basics. Coffee is prepared from the seeds of the coffee plant, a 5-10m high tree from the genus Coffea. The seeds, that we also call “coffee beans”, are contained in the berries that first need to reach maturation before being processed and dried. Nowadays, two species are used for commercial coffee: Coffea arabica, which gives Arabica beans, and Coffea canephora, which provides Robusta beans. Arabica beans have a sweeter, softer and more acid taste (berry-like) while Robusta coffee has a stronger, harsher and peanutty taste (grain-like).
If you are not already holding a cup of coffee while reading these lines, it is time to grab one.
One of the very important steps in processing the green coffee beans is the roasting step. During this step, the beans are exposed to a temperature of 180-250°C between 2 and 25 minutes. The beans are then cooled and can be eventually ground to prepare the holy liquid. Because it uses such high temperatures, the roasting step has a significant impact on the composition of the beans and therefore on the taste, aroma, and potential therapeutic effects. For instance, these temperature will trigger the chemical reaction between amino acids and carbohydrates. If you want to shine during your next family dinner, this reaction is called “Maillard reaction” and this is the same reaction occurring in your oven when you are baking bread or cookies.
Wait – did you mention “therapeutic effects”? Does it mean that coffee could have some kind of health benefits?
Believe it or not, but the dark liquid that you hold in your hands every morning contains hundreds of compounds – so it is not so surprising that some of them could have a positive or negative effect on our organism. The dry green beans are mostly composed of carbohydrates (around 60%), lipids (8-18%) and proteins/peptides/amino acids (9-16%) . So far it sounds quite boring, but having a look at the remaining compounds starts to be much more exciting. Besides these macro-nutrients, coffee also contains phenolic compounds, including chlorogenic acids, cinnamate and benzoates derivatives; as well as other compounds with nice exotic names, such as cafestol and kahweol (from the family called “diterpenes”), melanoidins, trigonelline, paraxanthine, theophylline and theobromine.
I am getting a headache with all these new words. I thought that coffee mostly contained caffeine?
Indeed, besides all these lovely-named compounds, coffee does contain caffeine. However, the potential positive effects of coffee are mostly explained by the other compounds present in coffee – and not by caffeine. Let’s keep caffeine for the second part of this post, and focus first on the rest.
There is a lot of literature available on the topic “does coffee show potential health benefits?”, which tends to agree that the chlorogenic acids may for instance have antioxidant properties, inhibit DNA methylation, and inhibit platelet activity, meaning that coffee could lower the risks for some cancers (mostly endometrial, oral, prostate, liver and pharynx), reduce cardiovascular diseases, and decrease risk for type 2 diabetes [2-4]. Since most of the findings reported so far are based on observational studies, it is still way too early to recommend coffee consumption to everyone. We need more experimental studies which also take into account the impact of other lifestyle factors and standardize the size and type of coffee tested.
And… Coffee can have some negative effects, mostly linked to its content in caffeine.
Aaaaah, caffeine, let’s talk about it!
Do you know that caffeine is not only present in coffee, but also in more than 60 other plants, including tea and chocolate? The amount of caffeine per cup of coffee depends on multiple factors: the method of preparation, the volume used, and the type of beans. Robusta beans contains around 2.2% of caffeine, while Arabica has around 1.2%. In general, a cup of coffee has between 40 to 140 mg of caffeine . A typical espresso (30 mL) has around 40 mg of caffeine, a black tea around 30 mg, a Coke (360 mL) 40 mg. Just keep in mind that it can reach concentrations that are 6 times higher depending on the roasting and the barista!
Caffeine reaches its maximal concentration in blood quite fast, around 15-45 min after ingestion of the holy liquid. Its elimination depends on the physiological status. Normal healthy adults eliminate half of the concentration (what we call the “half-life”) in 3-6h, but women taking oral contraceptives will need 5-10h and pregnant women 9-18h, especially during the last trimester where the elimination is slower . This is why the European Food Safety authority recommends pregnant women to stick to less than 200 mg caffeine intake per day.
What – taking the pill has an effect on the elimination of caffeine?
Absolutely. This is due to an interaction between caffeine and the estrogens (present in most of the oral contraceptives) at the site where the metabolism (transformation) occurs. Caffeine is metabolized in the liver by an enzyme called CYP450 1A2 (another topic if you want to shine during your family dinner), which transforms caffeine into its metabolites that are then eliminated in urine. Estrogens are also metabolized by the same enzyme. If you have both caffeine and estrogens that you need to metabolize using this enzyme, you end up with the same situation than when you drive to South of France in summer and have to wait hours in the charging zones. Too many cars for too little counters – please wait for your turn.
So what are the possible negative effects of caffeine on our body?
If you are a coffee lover, you might have already faced once some severe issues to fall asleep because you just had a strong Ristretto in Italy or a large Americano in New York in the evening. If you are a coffee addict, you may also have seen the effect of caffeine on your heart rate and blood pressure, with tachycardia (increased heart rate), palpitations, nervousness or headaches. Heavy coffee drinkers seem to also be at higher risks for some cancers (bladder, pancreas), although this is not supported by enough scientific evidence yet.
Does it mean that drinking decaffeinated coffee would be the perfect solution, then? But decaf coffee… It is well-known that it doesn’t taste like real coffee, does it?
It depends on the method used to extract the caffeine from the coffee beans. The best method is the one which can remove the caffeine only while keeping the other compounds in the bean and without adding any “artifact” which would alter the taste and properties of coffee. We call that “extract” the caffeine, using a solvent or liquid for which caffeine has a strong affinity, stronger than for the beans themselves. Several methods are nowadays used to decaffeinate coffee, the most widely used being the solvent decaffeination, the decaffeination using carbon dioxide, and the water decaffeination. All methods are performed on the green beans, before roasting .
The solvent decaffeination is the first method developed to decaffeinate coffee. It can be performed using two approaches: the direct extraction of caffeine using a solvent, or the water extraction of the caffeine followed by solvent extraction of caffeine from the water part. In both approaches, the first step is to steam the green beans to increase the moisture content, which enables the release of caffeine. The direct solvent extraction is typically carried out using dichloromethane or ethyl acetate. Dichloromethane is less used because of its relative toxicity – not for us, but for the environment. Ethyl acetate is even safer (it is actually a natural component present in many fruits) and approved by the FDA. In the water extraction approach, the beans are stepped in hot water which dissolves caffeine. The water phase is then separated from the beans and treated with a solvent to remove caffeine. Finally, the residual water is returned to the beans. This method has the advantage that no solvent is in contact with the beans.
Different versions of the water decaffeination exist. In the Swiss water decaffeination (because first developed in Switzerland), the most common, the green beans are soaked in hot water. Since the solubility of caffeine in water is much higher at high temperature (70% at boiling water vs 2% at room temperature), the caffeine can be extracted in hot water – as well as other components responsible for the flavor. This water then circulates through an activated carbon filter to remove the caffeine and is sprayed back onto the beans, so that the extracted flavors can be re-absorbed by the beans.
The decaffeination using carbon dioxide (CO2) is the most selective one – meaning the one which will extract caffeine but not the other compounds.
CO2? But that is the gas surrounding us, that we are all exhaling, isn’t it? How can such a gas extract caffeine from a coffee bean? This sounds surrealistic.
Time for a chemical intermezzo. When carbon dioxide is heated at a temperature higher than 31.4°C (90°F), and subjected to a pressure higher than 72 bars, it reaches the state of mater called supercritical. If you have ever followed a thermodynamics lecture, you have already seen a phase diagram, a chart which shows the conditions at which the distinct phases of matter (gas, liquid, solid) occur and coexist:
When CO2 is heated beyond the so-called critical temperature (31.4°C) and put under a pressure higher than its critical pressure (74 bar), it reaches the liquid-vapor critical point, a condition where both liquid and vapor (gas) phase coexist. Beyond this point, CO2 is therefore found under its supercritical state. It also happens for water, but the critical point is observed at 374°C (705°F) and 220 bar – conditions that are hardly ever observed in your kitchen.
***End of the chemical intermezzo***
What do we then do with this surrealistic supercritical carbon dioxide?
The green beans are first mixed with water, as in the solvent decaffeination technique. They are then loaded onto an extractor, where supercritical CO2 will flow through to extract caffeine. Extra water is added to the CO2 to remove the caffeine, allowing for recycling of remaining CO2 for the next cycles.
The supercritical CO2 is perfect to extract caffeine: it has no affinity for carbohydrates (starch and sugars) and peptides/proteins, which are essential for the flavor and aroma of brewed coffee, it also does not extract other water-soluble compounds (on the contrary of the other decaffeination approaches), it is tasteless, non-toxic and more environmental friendly.
Decaffeination using carbon dioxide clearly leads to a product of superior quality compared to the other techniques.
Does it also mean that carbon dioxide can remove absolutely all the caffeine molecules present in the beans?
Almost – up to 99.7% of caffeine. This is in accordance with the European guidelines, which state that a coffee can be referred to as “decaffeinated coffee” if it has less than 0.3% caffeine (UK asks for less than 0.1%). There is not regulation in the US, but commonly most of the brands aim for more than 97% of caffeine removal.
So we have different methods that can be used to decaffeinate coffee, which lead to a different end product in terms of residual caffeine content, taste and aroma, and potential health benefits. How do I know what kind of method has been used for the coffee I drink?
Since this information is rarely mentioned on the package itself, just ask Google – even though sometimes the information is difficult to retrieve due to marketing/intellectual property reasons.
I asked Google and this is the (non-exhaustive) information I have found [6,7]:
Starbucks: solvent extraction with dichloromethane
Costa: Swiss water method (modified)
Caffè Nero: supercritical carbon dioxide
Nespresso Grands Crus: water-based method
Douwe Egberts Instant coffee: solvent extraction with dichloromethane
Nescafé: Swiss water method
Simon Levelt organic coffee: supercritical carbon dioxide
Lavazza: supercritical carbon dioxide
Illy: solvent extraction
What about the possible health benefits from decaffeinated coffee, since its composition is slightly different than the caffeinated version?
We still lack more experimental studies to be able to give a clear answer to this question. However, some relevant studies have been published in the last couple of years which investigated the possible effects of decaffeinated coffee on Alzheimer’s disease, total mortality, cardiovascular disease or type 2 diabetes. An interesting one has been published this year in the British Journal of Nutrition, where the authors compared the effect of regular coffee, regular coffee with sugar, and decaffeinated coffee on insulin resistance as well as glucose concentration and other fancy hormones involved in diabetes, and this in a pool of 17 young healthy participants . Not a very impressive number of subjects, but at least they all drank the different beverages, as well as “control” drinks (water and water with sugar). What has been observed is that a moderate decaffeinated coffee consumption (equal to 2.5 cups, i.e., 300 mL) improved insulin sensitivity in the subjects compared to water intake – an effect not observed with regular coffee. This might be explained by the presence of chlorogenic acids and trigonelline in decaffeinated coffee which both have a positive effect on insulin sensitivity and glucose, while this effect is offset when caffeine is present. Interesting findings, but what is surprising is how they selected the tested coffee brands: they wanted the brand with the lowest amount of caffeine for the decaffeinated coffee (Melitta descafeinado Clássico, decaffeinated by solvent extraction, using ethyl acetate) and the one with the highest proportion of chlorogenic acids in the caffeinated version (Café do Ponto Araulto). I am not fluent in Portuguese but it looks like they did not select the same brand, which is questionable. Also, this was not a long-term study and only limited to healthy young men, so more evidence is definitely needed before being able to say that decaf coffee could play a positive role in type 2 diabetes or/and glucose homeostasis.
Or in other diseases…
- Decaffeinated coffee can be as good as the caffeinated version but it is also very dependent on the technique used for decaffeination
- Decaffeination using supercritical carbon dioxide seems to be the best to keep the flavor, aroma, and potential antioxidant properties from the green beans.
- It is relatively easy to find information on the decaffeination method used by commercial brands, but much more challenging to get this information when you go out.
- Decaffeinated and caffeinated coffees both seem to have positive health effects at moderate consumption (less than 2-3 cups per day) but more experimental research is needed to draw clear conclusions and decipher the possible differences, also depending on the decaffeination method used.
- None of the method used for decaffeination is toxic on our organism. The solvents used are in any cases evaporated from the beans.
- Caffeine is not bad per se if consumed at moderate doses. Risk for sleeping problems, cancer, and cardiovascular issues increase along with the dose, and are also different for everyone.
- We also lack solid evidence on risks linked to caffeine intake in pregnant women, but it seems that the overall risks for the fetus increase with the amount of caffeine. The guidelines recommend to stay below 200 mg of caffeine per day. Decaffeinated coffee is a good alternative.
 I.A. Ludwig, M.N. Clifford, M.E. Lean, H. Ashihara, A. Crozier, Coffee: biochemistry and potential impact on health. Food Funct 5 (2014) 1695
 K. Nieber, The impact of coffee on health. Planta Med 83 (2017) 1256
 S. Bidel, J. Tuomilehto, The emerging health benefits of coffee with an emphasis on type 2 diabetes and cardiovascular disease. Eur Endocrinol 9 (2013) 99
 A. Wang et al., Coffee and cancer risk: a meta-analysis of prospective observational studies. Sci Rep 6 (2016) 1
 K. Ramalakshmi, B. Raghavan, Caffeine in coffee: its removal. Why and how? Crit Rev Food Sci Nutr 39 (1999) 441
 Decaf coffee: the best solvent-free, low-caffeine, full-flavor beans. https://www.telegraph.co.uk/food-and-drink/drinks/decaf-coffee-the-best-solvent-free-low-caffeine-full-flavour-bea/ (accessed Oct 2018)
 Commercial brands websites
 C.E.G. Reis et al., Decaffeinated coffee improves insulin sensitivity in healthy men. Br J Nutr 119 (2018) 1029.
All credits to A. Grand-Guillaume-Perrenoud for the phase diagram used in this post.