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July 26, 2017

Infrequently Asked Questions: How does 'nitro' coffee work?

An emerging trend in specialty shops--Greenstreet and Rival Bros., among others--is the nitrogen-infused "nitro cold brew." And while it's delightfully smooth and creamy even without the addition of milk, one has to wonder: What's happening to make it so delicious?

Curious, we reached out to scientist and Function Coffee Labs owner Ross Nickerson for an answer. 

What's the science happening when you infuse nitrogen with coffee? With cold brew, in particular. 

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There is a pressurized vessel containing nitrogen that's been pumped in. A line from this gets connected to what essentially amounts to a keg of cold-brewed coffee. Nitrogen doesn't dissolve very well in water; 98 percent or so of your coffee is just water. So, the nitrogen and coffee mixture gets forced through a restrictor plate--a plate with a bunch of tiny holes. This helps get the gas into the liquid. This is almost always done with cold brew, though there are a few shops that put flash-chilled iced coffee, or hot coffee that is cooled very rapidly, on nitro.

How does it impact the taste?

The nitrogen actually doesn't really affect the taste of the drink, at least initially. But, it drastically changes the mouthfeel--all those tiny bubbles give it a thick, creamy, heavy body and a pleasant effervescence. Over time, it does help to preserve the taste. Without nitrogen being infused into the drink, oxygen gets into the coffee which, unsurprisingly, oxidizes the flavor compounds--similar to how rust forming on iron is an oxidation process, which changes the properties of the iron.

What's the difference between infusing with nitrogen versus carbon dioxide?

Carbon dioxide bubbles tend to give a more bitter taste; most beers are "carbonated" with carbon dioxide, which leads to the formation of carbonic acid, which is a very bitter-tasting compound. However, darker beers like Guinness typically get infused with nitrogen rather than carbon dioxide to give the rich, creamy body that is desirable without increasing the bitterness to unpleasant levels.

When did coffee shops discover this worked well with coffee? Is this a new discovery or something the mainstream is just now picking up on?

There's some debate over who actually "invented" nitro cold brew, but Stumptown Coffee Roasters in Portland, Oregon, was certainly one of the pioneers in 2013. So, this is pretty new for a drink that's been consumed for several hundred years. The process has been used in beer for a lot longer, so it's really just a new application of existing technology.

Could someone infuse with nitrogen at home? 

Yes, absolutely. It's just like kegging your own beer, if you're a home beer brewer. It's not too difficult, but I don't think the average person who likes cold brew because of the convenience of being able to prepare it the night before will want to invest the time or money into doing it at home.

Beer brewers have done this for a long time, right? 

Yes. Although Guinness is 258 years old as a company, they started nitrogen infusion in 1959.

Is there a downside to infusing with nitrogen?

The "cons" would be the added time and cost. Whether or not people prefer their cold brew on nitro or just as normal cold brew is up to them. It's not something upon which everyone agrees. 

Anything to add? What are you seeing as the next big thing in coffee? 

One thing we're seeing more of in Philly is flash-cooled iced coffee--small specialty shops including Function Coffee Labs, Ultimo, Ox and even some of the bigger players like La Colombe are doing this. This can be done in big batches so that it's ready to serve quickly, or various different pour over-type brewers can be used for a brew-on-demand, single-cup version. With specialty grade coffees, the unique flavor notes that make each one special--think: different grape varietals from different regions having really different tastes--make it into the cup, which doesn't happen with the cold brewing process.

Some roasters are now also adding hops to cold brew to add back some of the flavor complexity that normal cold brew lacks. And coffee cocktails--come on, Pennsylvania, make it easier for us to do these--are pretty trendy!