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What Type of Water Will Help Me Brew the Best Coffee? (Updated 4/10/16 – scroll down)
The article we are reviewing today is entitled:
“The Role of Dissolved Cations in Coffee Extraction,” Christopher Hendon, et. Al, Journal of Agricultural and Food Chemistry, 2014, 62, 4947-4950
As many of you may know, all water is not equal, especially when it comes from a municipality into your home. You may have noticed a sort of crusty scaly compound form around and near your water pipes or inside your tea kettles, or maybe you have experienced the scourge of soap scum. This usually would mean you have ‘hard’ water. Water hardness is basically the amount of dissolved minerals found in your water, with the most common minerals being Magnesium and Calcium. If you have an excess of those ions floating around in your water, your water is considered ‘hard.’
Now, there are a ton of compounds in coffee, and when you brew those compounds with hot water, you are dissolving and extracting them from the coffee bean. However, you may have noticed, that if you brew coffee at home (Sunnyvale, CA for this example) and then brew the same coffee somewhere else (perhaps at my dad’s place in Portland, Oregon), the coffee may taste slightly different, even if I am weighing out the same amount, grinding it the same, using all the same materials, and assuming the roast date isn’t too far apart when making these two cups. There is a good chance that this may be due to the hardness of the water you are brewing with, and the ability of that water to extract different amounts of the same compounds from the coffee. The question then becomes, what hardness or minerals do I want in my coffee to extract the ‘best’ cup?
The authors of this article have a clear goal: to define the ‘ideal’ water composition for the “ideal extraction of flavorsome compounds in coffee.” While not a totally new idea, it apparently hasn’t been answered very well. According to the authors, the Specialty Coffee Association of Europe has observed this effect, and has offered a guideline for the ‘ideal’ Total Dissolved Solids (TDS) amount in water. Unfortunately, their guideline is a little vague, as it doesn’t call out which dissolved solids, just that 300 ppm total makes for a ‘favorable’ extraction. Therefore, to be more precise, the article focuses on three major dissolved cations that are able to extract out major coffee constituents: Sodium, Magnesium, and Calcium (Na+, Mg2+, and Ca2+, respectively). The coffee compounds detailed in the paper are captured in the image below:
One downside of this paper is that they only focus on these 7 compounds, however, they are all important and in abundance in roasted coffee. Lactic and malic acid typically produce a sour flavor, while citric acid can taste sweet. Quinic and chlorogenic acid are known to be pungent and not tasty, while caffeine doesn’t need an explanation. Finally, eugenol produces woody flavors.
There is a lot of quantum chemical math in this paper, so I will not go into detail about all that, but basically they define the thermodynamic relative binding energy between the compounds above (plus water) and the common ions. The results were pretty clear – Magnesium had the highest binding energy across all compounds, followed by Calcium and Sodium as a distant third. This points out that Magnesium would, by a small amount, bind more of the desirable flavors of coffee, although on the flipside it would greatly increase the extraction of quinic and chlorogenic, which are undesirable.
The authors kindly note that the presence of carbonate/bicarbonate in water would counteract the extraction of chlorogenic acid, as these and other bases interact strongly with chlorogenic acid and would neutralize some of it.
So the take home message from this study is that if you want to extract the most of these 7 compounds from coffee, Magnesium rich water would be the best, while Calcium would be second best, and a mixture of the two with the proper amount of bicarbonate (to buffer the undesirable acids) would hit the sweet spot.
Overall, the article was fairly interesting, although it would have been nice to see some real world trials rather than computational chemistry and theoretical results. Finally, it should be noted that the author’s don’t call out an exact mineral composition in water that would produce the best extraction – they simply stated that high concentrations of Magnesium and Calcium would extract more compounds out of coffee, and that flavor really depends on the balance between the cations in solution and the quantity of bicarbonate present.
The AMAZING folks at Hershey and Hazel in Hong Kong are coffee nerds such as myself. In fact, Mr. Brian, a chemist by training who works at the shop, was also very interested in this subject. So interested that he had some salt solutions, including Magnesium Sulfate, that he was experimenting with to test this very topic. Once I spoke my conclusion that the flavor change from the additional ions would not be perceptible by normal people, he politely told me I was wrong and invited me to partake in an experiment! Of course, I could not object, and WHAM, he pulls out two bottles of salt solution and off we go.
Brian explained that he had been experimenting with this for quite some time, and would make certain [solutions] until he found one that he thought was good. He would add the solution to a pot of water, and would measure the TDS (total dissolved solids) before and after addition of his magnesium sulfate solution to ensure proper concentration. Although this wasn’t a controlled experiment, the TDS changed noticeably after addition. For this round, Brian used hershey and hazel’s Ethiopia Lime Gera.
Strong and pleasant lemon acidity (slaps you in the face with lemon), woody notes, baked apple on the finish. Quite a pleasant cup
V60 (with Magnesium Sulfate)
Holy heck what a difference. The slap you in the face lemon acidity was now a mild week old lemon water acidity, hardly perceptible in comparison to the control run. The cup became more astringent, and the finish also mellowed out.
I wish I had taken better notes on the tasting here, but the outcome is clear. I was 100% wrong about the flavor change being imperceptible – it was glaringly obvious. What an interesting experiment, and now my mind is racing about the possibilities here. I do maintain, like the article suggested, that there is no way (that I can think of) to selectively extract the positive flavor compounds. However, that doesn’t mean with careful and super fun experimentation that you could modify your coffee to highlight certain flavors. Let the experiments begin!