So this is a topic near and dear to my heart. Living in the South, one comes to appreciate things that keep us comfortable in the unbearable summer time from March to October. Recently, a small Twitter debate erupted sparked by Counter Culture Coffee’s Peter Giuliano. Peter brought up some great points that you can read here, some of which I’ll go into further down the page, but the best part about it was simply that it got me thinking. And as one can deduce from the Tweet-plosion that followed, it got a few others thinking as well.
With a bit of trepidation, I have to respectfully respond to Lorenzo’s blog post today about cold brew coffee.
Let me start out by stating this: I do not like the cold brewed coffees that I have tasted. Not one. Most of the time, the beverages have had harsh, negative taste characteristics. At best, they’ve been inoffensive but definitely not an exemplification of what we know great specialty coffee can taste like.
That said, I’m 100% open-minded. I would love to taste a great cold-brewed coffee. I am not interested in being “right” about stuff like this. I am interested in seeking truth and facts. I’m a big believer in the dialectic approach to this sort of stuff, despite what many might assume. To that effort, I have to point out that Lorenzo’s post has a few items I must take issue with. I’m glad that Lorenzo is open-minded though, as he stated in his footnote:
"I do not pretend to have a firm grasp of organic chemistry, and I readily admit that some of my conclusions from SCAA material and science journals may be very, very wrong. If so, please don’t hesitate to take me to school, specifically science class."
1) “According to research done by Lingle, et. al, in the Coffee Brewing Handbook (footnote 2), there was a significant decrease in the amount non favorable compounds, specifically Chlorogenic Acids (CGA’s), by about 100mg/L (the taste threshold being around 25mg/ml).”
This decrease, as stated in the “Coffee Brewing Handbook,” refers to coffee brewed at 70°C (158°F) vs 94°C (201.2°F). You can’t extrapolate “cold brew” extraction rates based on 158°F numbers.
2) "Mean taste thresholds for sodium chloride, sucrose, citric acid, and caffeine in the presence and absence of 1% linoleic acid are presented in Fig. 1. Thresholds were significantly higher (i.e., lower sensitivity) for the sodium chloride, citric acid, and caffeine solutions with added fatty acid… So, that tells me that with less fat content you will perceive more sweetness as there is less sensitivity to saltiness and bitterness from the caffeine."
The study you linked to involved a 1% linoleic acid solution. Coffee is roughly 0.01% linoleic acid.
3) "This was explained to me as the lightest solubles, also the first to extract, were placed at the top of the chart and the heaviest solubles, the last to extract (see the pattern here), were placed at the bottom. Let’s keep this in the back of our minds."
This is not true. The aroma-side of the flavor wheel is divided into three sections: enzymatic, sugar-browning, and dry distillation. Enzymatic flavors are those that come more from the green coffee, the sugar-browning from the Maillard and caramelization reactions, and dry-distillation from the carbonization phase of roasting. This has little to do with solubility, especially as they relate to taste. It IS true, however, that short-chain polar acids generally have higher solubility in water than sugars, and that many of the negative flavor compounds do take longer than acids and sugars to dissolve.
4) "By utilizing a short 45-120 second “bloom” with hot water, we are able to extract those easily dissolved volatile compounds (fruits and florals), and then by adding very cold water immediately afterwards we in effect trap the volatiles into the cold water brew itself, while finishing out the coffee over a 12 hour steep time to pull out more of the heavy compounds like sucrose and polyphenols and avoiding the potential extraction of negative compounds like CGA and trigonelline."
This is an interesting idea, and one that I’m interested in exploring as well (link to G+). However, don’t demonize chlorogenic acid or trigonelline, and don’t over-value your short polar acids! All of these, when present in balance, contribute to what we love about coffee flavors. It’s when they’re out of balance, or very commonly, when they’re not sufficiently supported by sweetness, that our palates register them as not pleasing.
5) One thing that cold-brewing does not accomplish, which there’s unfortunately little to no published research about, is the hydrolysis of hemicellulose. While 65-70% of roasted coffee is considered insoluble, as much as 15% is hemi-cellulose, which is hydrolyzable with heat and time. Hemi-cellulose breaks down into reducing sugars, which are typically associated with caramel-ly and savory sweetness. There is, again, pitifully little research I’ve been able to find on the subject, aside from acknowledgement that hemi-cellulose exists in those proportions in roasted coffee and that hydrolysis to reducing sugars occurs over time. In fact, the Lingle book refers to hydrolysis as the third-phase of brewing, following wetting and extraction.
That said, I’d love to try your hot-to-cold brew! There’s a lot to be learned about brewing, and it’s great to study the existing literature and experiment a bit, both in testing assumptions and exploring new variables. Thanks a lot, Lorenzo, for continuing the discussion!