The Science of Nitro Brews

Homemade Cold Brew Coffee to Drink for Breakfast

On the journey to nitro cold brew, which continues to be the up-and-comer of summer coffee drinks in the specialty coffee community, slowly spreading mainstream with Starbucks’ introduction of nitro brew earlier this year, one brewer started first with carbon dioxide. That, apparently, ruined the flavor of the coffee; but, it wasn’t a long leap from there to the more familiar method of bubbling up the stimulating brew in the way that beer is when it comes on tap, in a draft.

Like the steam heat pressure in an espresso machine, the nitrogen gas for nitro cold brew creates a tiny army of bubbles which create a creamy “head” (called a crema in espresso).

Stumptown, of Portland origin, was one of the first in the country to produce nitrogen gas infused cold brew. It was possibly the most exciting coffee experience I’ve had when I tried one for the first time. I hadn’t heard about it before I went along with my barista team on a coffee bar crawl; our supervisor ordered one for us all to sample and my jaw dropped. It streamed out of the tap smooth and light brown, developing that frothy head that creates the most delightful mouth feel, it was served without ice or other additives and it was absolutely perfect. I felt like I was drinking a beer except the bus was, obviously, different.

It’s not so simple as infusing the coffee with nitrogen gas (if that sounds simple to you at all). Depending on the shop, you have to brew the coffee either hot, letting it cool before percolating the nitrogen gas in with it, or cold brew it before infusing. According to Jill Krasny of Esquire, nitro cold brew is made when “cold-brew coffee [or cooled coffee] infused with nitrogen gas is released through a pressurized valve with tiny holes. As high pressure forces the cold brew past a disc, it creates a creamy, stout-like effect.”

At Stumptown they store the nitro brew in a keg to maintain both temperature and bubble formation. When I had the version at Starbucks, though I don’t know what their specific storage method is, I could tell it was different because it was less frothy and stayed cold for far less time.

Generally, I can’t drink Starbucks coffee black without a bit of a cringe; but, their nitro cold brew came close to Stumptown in that it was perfectly palatable with nothing added to it. It’s not clear why this particular brewing method may result in a better tasting brew, but I know it can’t be, as some have asserted, merely the quality of the coffee that does it; I know this because Starbucks tends toward darkly roasted, cheaper beans, particularly for their mass-produced beverages. To be clear, this is anecdotal and not a definitive assertion.

One of the explanations that makes the most sense is the fact and function of cold brewing to begin with. When a coffee is brewed hot, it loses flavor as it cools. The molecules change as the temperature drops, and sometimes adds different ones that can be less desirable. Particularly, the citrus notes tend to be lost as cooling occurs while more bitter flavors like dark chocolate are enhanced.

When a coffee is cold brewed, however, it is presumed that it is imbued with a more consistent flavor because it is given time to infuse and there is little-to-no temperature change from brew to consumption. Some food scientists also assert that note that temperature changes the flavor experience people have, so that could have an impact as well.

Beyond flavor, nitro cold brew is believed to last longer than other brews because the nitrogen may be stabilizing the flavor and other molecules in the coffee; a hot brew breaks down due to oxidation over time, and the nitrogen infusion pushes out the oxygen molecules, likely minimizing that effect.

Additionally, some claim that the texture of the nitrogen gas bubbles, the way that they play around inside your mouth and interact with your taste buds, gives the impression of sweetness and creaminess in the draft brew. It changes the way your mouth, and brain, translate the flavors at play, meaning that you’ll likely enjoy it quite a bit even if you’re used to coffee that’s light and sweet.

That texture is what makes nitro cold brew distinct from some of the bottled cold coffee options out there and your average soda beverage. Carbon dioxide is approximately 50 times more soluble in water than nitrogen, meaning that it results in bigger bubbles as the gas escapes. Nitrogen gas leaves the solution much more quickly, creating the finer army of bubbles, and more of a foam instead of a fizz. The carbon dioxide is less preferable, as mentioned above, because it creates a chemical reaction with water that results in carbonic acid. The point of cold brew for most people is that it has less acidity, making this option already undesirable. The added acidity also doesn’t mesh well with the natural bitterness of a coffee (as well as darker beers, like stouts) thus resulting in a sour and otherwise unpleasant flavor. Nitrogen gas does not have this acidic reaction, thus the smooth, palatable flavor.

Finally, from a business perspective, the process and supplies necessary for this new coffee advancement isn’t necessarily cheap; at least not until they fit/retro-fit coffee bars with kegs and taps automatically. At Stumptown, the nitro brew tends to be about a dollar more than their other drinks of the same size. Additionally, nitro cold brew is meant to be served without ice, meaning that your customers are getting an actually full cup instead of a partially filled one dispersed by ice cubes.

At Starbucks, they limited their nitro sales to a maximum size of medium, citing caffeine, though I’m fairly certain it was because selling a literal 20 ounces of the stuff would not be all that strategic. They were also offering a limited supply, and even with that size maximum, have often run out before midday at my local spot. Keep these things in mind if you’re looking to adopt this method, so far it seems most ideal for established brands with room to experiment, like Stumptown and Starbucks, or coffee bars that also happen to be alcohol bars that are already fitted for taps and kegs.


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