Iced Coffee

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.

It seems that people hold very strongly to particular ideals or perceptions in regards to iced coffee, which should come as no surprise when you realize that in an industry full of passionate people, passionate dialogue follows all too naturally. What did surprise me was the negatively violent force that was thrown towards the cold brew method. These came down quickly from people that are widely respected within the coffee community for their coffee-making prowess (footnote 1), which puts me in a very awkward position as my experiences have led me to make near opposite conclusions.

Now, by no means do I pretend to have all of the answers and have exhausted all potential avenues of research, nor do I believe these other highly regarded professionals to have done the same, albeit perhaps much more extensively than I. But, dammit, I have tasted great cold brewed coffee. What seems to be the most logical conclusion for me is that answer that we so often give to people who “Just don’t like coffee”. You just haven’t had a good one, yet.

Iced Coffee, out of all of the standard coffee beverages, seems to be the red headed step-child. The coffee that everyone offers, but no one really drinks or even likes for that matter, and in that regard I am grateful that someone with a bully pulpit the size of Peter finds the time to speak to this topic.

But respectfully, I disagree.

Solubility

Yes, hot water is a more effective solvent than cold water. A fact first brought to my attention by the myriad of substandard auto drip brewers functioning on a 14 minute brew cycle. You see, to make up for a lack of temperature, these brewers increase their extraction yield by extending the brew time. Obviously, aroma is something to be greatly enjoyed in a fantastic cup of coffee, and Peter says that by using hot water we are able to quickly and effectively pull out desirable compounds that a less efficient solvent will not.

  • "You can try to use cooler water, but this means that the coffee will dissolve incompletely; many of the soluble substances in coffee won’t make it out of the grounds and into the water."

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). Compared to other favorable compound extractions there is actually very little change in the presence of Malic Acid and Citric Acids (less than 6g/Liter each with a taste threshold of roughly 100mg/ml). So the negative organic acids are reduced at lower temperatures, with the positive organic acids not being terribly affected.

Now, what is substantially changed is the sucrose content and fatty acids. In a recent study on the effect of long chain unsaturated fats the following was found

  • 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. http://ajpgi.physiology.org/content/292/5/G1243.full

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. Add to that fact that most of the bitterness or off flavor in coffee doesn’t come from the caffeine, it’s do more to the presence of CGAs and trigonelline, compounds which are also less extracted with lower temperatures as Lingle, et al, also show that at lower temperatures it becomes more difficult to extract not only caffeine, CGAs, and phenols.

In the end the anti-Cold Brew argument is made thusly:

  • The technique tries to make up for the relative insolubility of coffee at cold-water temperatures by brewing for a long, long time. This creates the illusion that you have made coffee- the resulting liquid is dark and tastes something like coffee- but many of the coffee solubles have never made it out of the grounds and into the liquid.

As I’ve shown above, a lot of the solubles that have not made it out with the less efficient cold water are those that actually tend to add more negative flavor.

Volatility

Volatile compounds include all sorts of benzenes, CFCs, and even a popular decaffeinating agent dimethyl chloride. They are volatile because they have a low boiling point and at room temperature will evaporate faster than other soluble compounds like carbohydrates and proteins. Unfortunately, the wonderful aromatics of coffee are also volatile compounds that can be essentially “brewed out” of the finished product, like in the inefficient home drip brewers. Peter offers a clever fix to this in the iced coffee debate.

  • Cooling the coffee quickly, though, reduces volatility dramatically. This effectively locks the ephemeral volatiles (like floral and fruit notes) into solution until the coffee is warmed again. This happens on the coffee’s way down your throat (sorry to get graphic here), which sends a punch of beautiful volatile aromatics through your retro-nasal cavity to your olfactory receptors.

With this, I have no argument. It is absolutely correct. We will definitely come back to this one later. ;)

Oxidation.

Also called oxidative rancidity, it’s some pretty gnarly stuff. Oils and fats breaking down with the assistance of oxygen leading to off flavors. It happens faster at high temperatures, with exposure to oxygen, and in the absence of antioxidants (get it, ANTI - OXIDENT). Cool thing is, coffee is full of antioxidants. The aforementioned Chlorogenic Acid being one, as well as a host of other polyphenols (flavanoids) found in abundance in coffee. This seems like an easy one to prevent…keep your iced coffee, well, iced. Keeping the oxygen out is a little more tricky…the iced coffee for any longer term (20 plus minutes) storage needs to be in an anaerobic environment. Again, read on…

What then? Let’s take a look at that famous color wheel we call the Coffee Tasters Flavor Wheel:

Coffee Tasters Flavor Wheel - Right

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.

So, with the lack of negative solubles from the cold water brewing and stored in a nice cold oxygen free environment it seems as if we have a near perfect brew method, but wait! We also have a distinct lack of positive volatile aromatics from the lack of hot water brewing. That hot water quickly vaporizes and brings into the brew those elusive compounds. How do we fix that? We begin by brewing hot, and finish by brewing cold. What, that doesn’t make sense…or does it.

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.

  1. 100g of coffee, ground a little finer than drip
  2. 200g of hot water
  3. steep for 60 seconds then add
  4. 800g of ice water
  5. Steep for 12 hours at room temperature
  6. Strain.
  7. Fill kegs and connect to Nitrogen fed kegerator.
  8. Enjoy!

I will note that without being put into an anaerobic environment, which most of us have trouble procuring, Cold Brew iced coffee does not have a stable shelf life. I’ve heard it claimed that it will hold for three weeks or even longer, and I have to call bogus on that. Oxidation is oxidation, and it will inevitably ruin cold brew coffee. Make smaller batches and make it more often, just like we ask customers to do when buying whole bean coffee, freezers be damned. In this sense, you also help to create an illusion of scarcity, when if marketed right can really drive up the demand and/or price. Just a thought…

I’ve had some really great success with this method, and I guess it is a cold brew, but at the same time it’s not. I’d love to hear what you have found with your iced coffee experiments, because in the end, I’m just glad that we are talking about it. I’m going to start playing around a little more with this “Japanese Method” and see if I can’t make something that I’ll enjoy, and hopefully, my customers will too.

  1. No, I’m not alluding to Peter. In all of my interactions with him he has presented himself as thoughtful and level headed. But there are others that do not consistently apply the same level of professionalism (including myself from time to time).
  2. 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.