Have you ever wonder how much caffeine in your daily cups of coffee? Or whenever a brand advertised that their coffee are strong, why did they claim that? Or… how “strong” the coffee is among the brands?
If you also have those questions, then you are not alone. I have been wondering for so long that how can we compare the strength of commercial coffee packages, to know which one is actually… strong. The amount of caffeine is usually the factor to determine that. So, I decided to launch my really ambitious and long-term project: Relative comparison of caffeine amount in commercial coffee, or in other words, The Coffee Notebook. Before jumping into any experiments, let’s gather some information beforehand, and that’s what we, the lab people, do prior any experiments. We called it “Literature research”.
Buckle up, friends! It’s a long post!
Caffeine – Connecting from a Coffee lover’s point of view to a scientific point of view
Structure, crystals and some physical properties
One of the active components in coffee is caffeine (formula and crystals shape in the photo below). Some physical properties of caffeine are listed below (which are useful in the experiments).
– Caffeine appears as odorless white powder or white glistening needles, bitter taste.
– Melting point: 235 – 238 C
– Sublimation temperature: 178 – 180 C
– Fully decomposed at 285 C
– An acute fatal overdose of caffeine in humans is about 10–14 grams (equivalent to 150–200 mg/kg of body weight)
(Source: PubChem)
Solubility of caffeine in some common solvents
Caffeine content in coffee around the world – scientific reports
The first question is, how the caffeine content is precisely quantified?
The amount of caffeine could be precisely quantified by liquid chromatography (LC) and gas chromatography (GC). In brief, these systems have special columns that show different interactions with compounds soluble in the carrying solvents, and thus keep the compounds in the columns for a certain time, namely retention time (meaning the time that a solute spends in a column). Caffeine, or any pure organic compound, will be recognized by a characteristic retention time in LC and GC. Then, the area of the peak provide information on the amount of caffeine in the samples. That’s how caffeine is precisely quantified in the lab.
Below are the screenshots from 2 different research on caffeine content in Arabica and Robusta coffee beans. If you wish to read the full articles, email me for the copies.
(J. Agric. Food Chem. 2013, 61, 10772−10778)
The screenshot on the left is from the paper Variation in Caffeine Concentration in Single Coffee Beans published in 2013 in Journal of Agricultural and Food Chemistry (copyright by American Chemical Society). This is one of the good work on quantification of caffeine in commercial coffee that I have found so far. 20 grams of whole bean coffee was weight and ground (just like we do), and they took just 2 grams to brew in boiling water for 10 minutes.
Based on this work, the caffeine amount in Arabica beans ranges from 10.5 – 12.8 miligrams per grams of coffee (mg/g), and if you notice, the decaf coffee has 100 times less caffeine than our daily coffee. Arabica beans from Columbia has the highest amount of caffeine among the same beans. Note that beans with the highest and lowest amount are both from Brazil. Caffe Aurora Medaglia Doro, a blend from Italy, has the most outstanding caffeine content compared to other blends, so kudos to Italian friends!
(Journal of the Taiwan Institute of Chemical Engineers)
The screenshot is from the paper HPLC coupled to UV–vis detection for quantitative determination of phenolic compounds and caffeine in different brands of coffee in the Algerian market published in 2014 in Journal of the Taiwan Institute of Chemical Engineers (copyright by Elsevier).
The original unit of the right column is mg of caffeine per 100 grams of coffee, so to make it equivalent to the first paper, just divide all the number by 100. With that, among the coffee samples in Algerian market, Robusta coffee beans have more caffeine than Arabica beans. During the roasting process, we definitely lose some caffeine (as it sublimes at ~ 178 C).
Based on these 2 papers, the difference seems negligible for the caffeine content per grams, but our daily cup have around 10 – 20 grams of coffee, and that’s when it becomes significant. However, we enjoy the coffee not just because of the caffeine (to wake our mind) but also the taste, the flavor. From my experience, at the end of the day, choose whichever coffee that makes you feel happy, makes you want to enjoy it everyday, not because of its caffeine level.
Cold brew vs. Hot brew
Will cold brew be more convenient? Is cold brew really stronger than hot brew? Consider 40 grams of coffee brewed in 100 mL of water, let’s look at the table below.
| Water temperature & solubility of caffeine | 10.0 mg caffeine/gram of ground coffee | 20.0 mg caffeine/gram of ground coffee |
|---|---|---|
| Maximum caffeine: 40 g x 10 mg/g = 400 mg | Maximum caffeine: 40 g x 20 mg/g = 800 mg | |
| Cold water (0.6 g/100 mL) | 0.6 g vs. 0.4 g | 0.6 g vs. 0.8 g |
| Cold water (1.0 g/100 mL) | 1.0 g vs. 0.4 g | 1.0 g vs. 0.8 g |
| Room temperature water (2.2 g/100 mL) | 2.2 g vs. 0.4 g | 2.2 g vs. 0.8 g |
| Boiling water (66.7 g/100 mL) | 66.7 g vs. 0.4 g | 66.7 g vs. 0.8 g |
Based on the solubility of caffeine in cold water, room temperature water and boiling water, assumed the caffeine amount per grams coffee ranging from 10.0 – 20.0 mg (Arabica, Robusta, blend…), we can draw some conclusions:
- With an average amount of 11.5 mg caffeine per grams of coffee, caffeine from most of Arabica-based coffee and blends could be fully extracted by water whether we have cold brews or hot brews.
- In order to have the maximum caffeine amount from Robusta-based coffee and blends (which have 20 mg of caffeine per grams of coffee), hot brews are recommended.
Summary
- Arabica coffee beans averagely have 11.5 mg of caffeine per grams of coffee, while Robusta beans have more caffeine content. The caffeine content in the coffee heavily depends on the area of planting and roasting techniques.
- Due to the sublimation temperature caffeine at 178 – 180 C, it explains why dark roast blend has less caffeine than medium roast and light roast.
- Depends on the coffee blend, you can always get the maximum caffeine from cold brews and hot brews. However, roasting and brewing methods do affect the taste, so try different brands, different ways to figure out your style(s).
And ever since then, enjoy your delicious daily coffee cups!
There are very few (good) reports on quantification of caffeine in commercial coffee. I will keep you guys update if I found an informative one. Let me know what you think!
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