Nitro Cold Brew Coffee – Technical Note Matthew R

Nitro Cold Brew Coffee – Technical Note Matthew R. Hartings, Associate Professor of Chemistry, Author of Chemistry in Your Kitchen Department of Chemistry, American University, 4400 Massachusetts Ave, NW, Washington, DC 20016, USA [email protected] ABSTRACT: Nitro cold brew coffee has become a marketing and sales hit for coffee shops globally. The coffee’s novelty, ease of preparation, attractive textural and visual properties all play into consumer preferences. While there is certainly trade research studies that inform how some of the largest coffee producers approach making and preparing nitro cold brew coffee, there have been no published research articles that can inform smaller producers and purveyors of coffee. The work in this technical report was sponsored by the Parker-Hannifin Corporation who produces nitrogen generators that can be used by food retailers as a critical component of selling nitro cold brew coffee. This report details several critical aspects of dispensing nitro cold brew coffee (texture, foam quality and stability, and flavor) and compares the use of nitrogen to air in serving coffee. The report also makes some forward-looking recommendations for procedures that individual retailers might want to explore to make their nitro cold brew coffee stand out in the market. Nitro cold brew coffee is coffee that is stored cold and dis- generator is ideal for use in coffee shops in lieu of pressurized pensed using high pressure nitrogen, similar to Guinness nitrogen tanks. Proper use of pressurized gas tanks requires Draught or Boddington Pub Ale beers. Just as in these beers, training and on-site infrastructure. When performing safety nitro cold brew boasts a creamy texture that is primarily due to training with the chemistry majors at American University, the the nitrogen-based foam that forms on top of the dispensed cof- students are made aware that the pressurized gas tanks are some fee. The stability and quality of this foam is critical for long- of the most hazardous objects in the chemistry building. The lasting, consumer enjoyment of any nitro cold brew product. As simplicity of the Parker-Hannifin generators is that they do not seen through the analysis in this report, a quality, stable nitrogen require the same level of precaution and safe handling. While a source is critical for optimal dispensing of nitro cold brew cof- nitrogen tank stores 2200 psig of pressure, The Parker generator fee. While many bars are equipped to handle the high-pressure stores less than 125 psig. Additionally, nitrogen tanks need to nitrogen (and carbon dioxide) tanks that their beers require, the be replaced once they are empty. A forgotten order for new coffee industry (and especially many small coffee shops) do not tanks can put a halt on selling nitro cold brew until the filled have the proper infrastructure or worker training in place for tanks are delivered. The nitrogen generators from Parker Han- handling high pressure tanks. nifin run in the background and produce high quality nitrogen from the air. They act like an everlasting tank of nitrogen that never goes empty. While Parker nitrogen generators are certainly convenient, the research and results outlined in this report are valid with the use of either a nitrogen generator or a pressurized nitrogen tank. The goal of this report is to detail the protocols used in preparing nitro cold brew coffee and measuring relevant properties of the coffee. Many of the analyses used here (with the excep- tion of gas chromatography-mass spectrometry, GC-MS) can be performed in-house by any purveyor of nitro cold brew coffee as they refine and optimize their product. The report ends by making several suggestions of straightforward variations that coffee shops could take to make their particular version of nitro cold brew stand out from the crowd. Methodology Figure 1. Image of nitro cold brew coffee dispensed from a pres- Coffee was stored and dispensed from a Komos double tap surized keg. kegerator with 5-gallon, ball lock Cornelius kegs. The kegs The Parker-Hannifin Corporation, who supported the work in were connected through tubes to the pressurized gas or the dis- this report, supplied a beverage dispense nitrogen generator that pensing tap using screw-end, ball lock disconnects. The gas was used for pressurization and dispensing the coffee. This source was connected to the kegs through a gas pressure regulator set to 50 psi. Note: When connecting high pressure tanks, different high pressure regulators must be used for nitrogen and inherent that a beverage continue to be able to deliver foam to air. The Parker generator can use a standard air regulator, com- the customer as they continue to drink it. That is, the coffee monly available. should retain some foam within its head after every drink. To make the coffee, 12 ounces of Starbucks French Roast and In general, for this experiment, around 18 mL of coffee (~ 0.5 20 ounces of Starbucks Pike Place were ground on the coarsest ounces) was dispensed into a clean glass. The coffee was poured setting using a Capresso Infinite Grinder. The coffee grounds into a second container. The mass of coffee in both containers were steeped at 39 °F (4 °C) for 24 hours in a 5-gallon food was measured. The amount of mass remaining in the original grade container with 1.4 gallons of water. This cold brew container is indicative of cling. For measuring this property, method produces a 2X concentrate. The coffee was filtered two different scenarios were compared. In the first scenario, through a 13” non-woven filter cone in a 12” chinois strainer. coffee whose foam had not fully formed was poured. Cold brew After straining, the volume of coffee was doubled through the coffee is much like Guinness in that it takes time for the foam addition of water. The coffee was added to the keg. The keg was to develop as the dissolved nitrogen gas comes out of solution. connected to the tap and to the gas source and pressurized. The This process leads to the distinctive formation that is observed coffee properties were monitored each day for 1 week after in both Guinness Draught and nitro cold brew coffee (see Figure pressurization. Other than flavor degeneration in the air-kegged 2). In this scenario (pre-foam), there is very little foam. There- system, there was very little variation in the other coffee prop- fore, there should be less cling to the glass. In the second sce- erties over time. nario, the foam was fully allowed to form before pouring. The There are several measurements described in this report. For results from this test are shown in Table 1. each measurement, results found using compressed nitrogen Table 1. Foam and Viscosity Data were compared with results found for using compressed air. Volume (Estimates of the solubilities of gasses found in the pressurized fraction of Gas Coffee foam in Foam cling Line Solubility coffee at 39 °F (4 °C) are shown in Table 1.) pressurized coffee (g retained/ g spread test (mole Several tests were performed to assay the quality and quantity with (%) coffee) (cm/g) fraction) 10-5 of foam produced. The volume of foam produced (per volume Before foam: 2.6 ± 0.7 Nitrogen 12.8±0.9 0.26 ± 0.02 N2: 5.9 of coffee) was measured using a 25 mL graduated cylinder and After foam: a digital camera. Foam cling, the amount of foam retained by a 4.1 ± 0.5 glass after a pour, was analyzed using a mass balance. Foam Before foam: 3.2 ± 0.2 N2: 4.6 stability was assessed by monitoring foam volume after the in- Air 11.4±0.7 0.26 ± 0.01 After foam: O2: 2.5 itial pour as a function of time. 4.2 ± 0.5 A line spread test was performed to assess any differences in Ar: 0.12 viscosity. For this test, a sheet was printed with concentric cir- CO2: 0.12 cles with increasing diameters. This sheet was placed beneath a clear sheet of plastic. A tube with an internal diameter of 2 cm was placed on top of the plastic over the center ring on the sheet. A known mass of coffee was poured into the tube. The tube was lifted, and the spread of coffee was measured. Finally, a flavor analysis was performed on the coffee. A 100 m PDMS SPME fiber was incubated in the headspace above a sample of coffee for 30 minutes at 140 °F (60 °C). In that time, the fiber absorbed the volatile compounds from the coffee. The adsorbants on the fiber were analyzed using a Shimadzu GC- MS. Analytes were identified using a database from the Na- tional Institute of Standards and Technology. Results Foam production. Foam is an integral part of the experience of drinking beverages.1 Beer is the most prominent case in point, but there have been several studies of the science of es- presso foams (crema) as well. There are several macromole- cules that are responsible for the retention of gas within bubbles in these drinks. In both cases, some proteins and extracted pol- Figure 2. Illustration of the foam formation in nitro cold brew cof- ysaccharides enable foam formation and retention. For these fee studies, foam volume per total coffee volume was assessed. What is observed from this data is that, for both air and nitro- For these measurements, it is helpful to have a ruler to cali- gen, there is more mass remaining in the original container for brate the sizes observed in the image (see Figure 1). Table 1 the scenario after foam formation than before foam formation.

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