A 2020 Literature Review with Guidelines
Purity Coffee wants consumers to have more choice in coffee to meet their health goals. One of the main choices we make is how to brew our coffee. There are a multitude of methods for making coffee, and each one influences which of the hundreds of compounds are extracted. For the past few years cold brewing methods of preparation have become popular, adding to the crowded array of brewing methods.
We often get questions about cold brew coffee, and we felt it was time for a survey of the literature from peer-reviewed research that has been published in scientific journals. The internet is full of theories and practices, some are accurate, and others are conjecture.
Our review has revealed that scientific research has barely begun on cold brew. And, as always with published studies, we are rarely told what type of coffee was used, let alone what level of roasting was done. Coffee quality varies widely, so we look for results that can be generalized or representative of an incredibly complex food product. We know that coffee is extremely complex, and many beneficial compounds can be created, destroyed or left untouched by different brewing methods at different temperatures. Cold brew is no exception for this rule.
Health Points of Cold Brewed Coffee
What is Cold Brew Exactly?
The concept of cold brew is that ground coffee is extracted with water at room temperature (“ambient” = not chilled or heated) or cooler and steeped for an extended period of time to extract flavor compounds and soluble solids from the coffee. The key point is that the water is not hot. The brewing process swaps time for temperature – instead of brewing with near-boiling water over a few minutes, cold brewing typically uses cool water and extended periods of time (12-24 hours) to extract an optimal amount of flavor compounds and solids from the ground beans. Cold brew flavors vary widely from coffee brewed at higher temperatures.
Healthy Cold Brewing Point 1:
Keep Pathogens Out, Keep Anti-Microbial Compounds in
Anyone doing cold brewing must consider food safety. Using water that is not near boiling increases the risk that any mold or pathogens, that may be on the coffee or the brewing device, will develop. Cold brewing in a refrigerator is considered safer than ambient brewing, but still yeast, mold and bacteria can grow and survive at these temperatures. We have all experienced products in our fridges to which this has happened, and coffee is not immune.
Yeast, bacteria, and mold can all survive at ambient temperatures (danger zone 40º to 140ºF). Psychrophiles (i.e., Listeria monocytogenes) are a concern even under refrigeration. Sources of microbial contamination include water, containers, equipment, environment, personnel, and ingredients (Zuniga, 2016). Both Oregon State University and Cornell University conducted challenge studies by inoculating refrigerated temperature (4°C, 39.2°F) cold brew coffee from a commercial processor with Salmonella species, Listeria monocytogenes (L. mono), and Escherichia coli. Viable cells of all of these were found between 7 to 14 days after inoculation (Daeschel et al., 2017). L. mono is the pathogen of greatest concern for cold brew coffee production and can be controlled with thorough cleaning of equipment and the environment (Lopez, 2020).
A risky concept in the coffee industry is that coffee is its own antiseptic, which is partially true, where certain concentrations of caffeine and other compounds are inhibiting, not necessarily killing, some strains of bacteria. However, leave a cup of coffee by your computer for a few days, or forget to empty your brew basket full of grounds before you go on vacation for two weeks, and you will clearly see that coffee does allow growth of organisms.
That said, there are studies showing the anti-microbial compounds produced during roasting, and the (potentially) low level of nutrients present to support microbial growth (Daglia et al, 1994; Almeida et al, 2004). Caffeic acid and trigonelline showed similar inhibitory effect against the growth of microorganisms. The antimicrobial activity of caffeic acid was appreciable antibacterial activity against Pseudomonas, E. coli, S. aureus, and Bacillus cereus (5-6. Garrote, et al, 2004. Baranowski, et al, 1982).
Caffeine, chlorogenic acid, and protocatechuic acid showed particularly strong effect against certain pathogens, while trigonelline, caffeine, and protocatechuic acids showed potential natural antimicrobial agents against Salmonella enterica. (Almeida et al, 2006).
Instead of pointing to coffee as its own preservative when cold brewing, rather consider the above evidence as beneficial to maintaining gut health. Drinking a couple of glasses of clean, safely prepared cold brew could contribute to overall gastrointestinal well-being. With this in mind, an exceptionally healthy specific coffee roasted conscientiously for gut health would make an exceptional tonic. More on this in a bit.
Healthy Cold Brewing Point 2:
Choose a Roast Level and Grind Size Optimum for Antioxidant Activity
The most significant healthy, antioxidant compounds impacted by brewing temperature are chlorogenic acids (CGA). Of all plant constituents, coffee has one of the greatest concentrations of CGA. Because of the high content of CGA, coffee is considered the most important contributor to antioxidant intake in many populations, since people drink it habitually and, in many cases, multiple times a day.
In one study, CGA and caffeine were found at higher concentrations in cold brew coffee made with medium roast coffees, rather than dark roast. The grind size did not impact CGA and caffeine concentrations of cold brew samples significantly, but caffeine concentrations in cold brew coarse grind samples were considerably higher than their hot brew equivalents. CGA concentrations and pH were comparable between cold and hot brews. Considering that most acids in coffee are highly soluble and extract quickly, this indicates that the difference in acidity of cold brew coffee is likely not due to CGA or caffeine concentrations (Fuller & Rao, 2017).
Interestingly, this same study determined that caffeine and CGA concentrations reached equilibrium according to first order kinetics between 6 and 7 hours instead of 10 to 24 hours outlined in typical cold brew methods. Brewing times near 400 minutes are adequate to extract the majority of available caffeine and CGA in medium and dark roast beans prepared at medium and coarse grinds. However, no significant differences were seen in CGA concentrations between cold and hot brews, due to the solubility of CGA.
In sharp contrast, another study found that considering grind size, particles of 0.65mm had significantly higher antioxidant potential than 1.15mm and 1.65mm. For brew time, 24 hours had the lowest antioxidant potential, 18 hours was better, but 30 hours had twice as much antioxidant potential as the 18-hour brew (Morrisey, 2019). The researcher’s final recommendation was, “If brewing cold brew coffee for 18 hours, a smaller grind size (0.65mm) would yield significantly higher antioxidant potential than coarser grind sizes (1.15mm and 1.65mm).”
Healthy Cold Brewing Point 3:
Choose a Grind Size and Roast Level for Gut Health
An additional study indicated that cold coffee brewed under coarse grinding and 22 hours of extraction exhibited the highest values of total dissolved solids, extraction yield, pH, titratable acidity and CGA content (Cordoba, 2019). A quick mention of the difference of pH and titratable acidity: pH represents how much acid is in the brewed coffee, regardless of how strong the acid tastes; whereas a titration measures how strong that acid tastes. Coffee has numerous acids, like citric, malic, acetic, lactic, etc. Each acid has a different strength of tartness on the tongue and different molar weight.
In a previous article, we delved into acidity and how much it impacts gastrointestinal issues (particularly acid reflux). Coffee studies on stomach and gastrointestinal issues are an area of active research and conclusions vary widely. Toxins have been known to cause stomach issues and may be present in lower quality and stale coffee. Some chemical compounds naturally found in coffee may stimulate gastric acid production, depending on the type of coffee and a person’s genetics. The pH values of the cold and hot brew samples were found to be comparable, ranging from 4.85 to 5.13, which, incidentally, are the same ranges of bananas, pumpkin and watermelon. In other words, although the blogosphere accuses the acidity of being the culprit for heartburn, it is likely some other compounds are to blame. These compounds may be related to poor quality coffee that contain mycotoxins or rancid oils. Or it may be the caffeine.
In Cordoba’s (et. al.) study, all cold brew coffee samples had lower titratable acidity values than their hot counterparts, but hot brew had more CGA. Cold brew coffees prepared using 14 hours and a coarse grind scored the highest taste points with strong sweetness, medium bitterness and acidity. These are the common characteristics quoted about cold brew everywhere on the internet, however brewing technique can provide a much wider range of experiences.
Cordoba also noted that particle size distribution from the grinder played a large role in the chemical composition of cold brew coffee. Having a narrow grind size distribution is important for evenly transferring of soluble compounds into the brew. This means that the more accurate your grinder is, where it has a narrow range of size particles (they are more uniform—not having some like powder while others are like chunks), the more you can focus on adjusting for the compounds that you want to bring out in the coffee.
The most remarkable research specific to cold brew and gut health was conducted in 2017 by Kwang-Soon Shin in South Korea and revolved around the crude polysaccharide (CCP-0) and their immune-stimulating activities. CCP-0 are carbohydrates that boost the immunity of your digestive system mainly comprised of galactose, mannose, arabinose and uronic acid. Results of the research indicate that CCP-0 isolated from cold-brew coffee can serve as an inducer of the systemic immune system and activate macrophage function and intestinal immunity. Macrophages and dendritic cells are distributed throughout the body and play important roles in pathogen detection and tissue homeostasis (Cain et al, 2013).
In addition, Peyer’s patches are lymphoid tissues distributed throughout the small intestine and the ileum and contain lymphocytes, macrophages, dendritic cells and microfold cells (important for antigen uptake). Peyer’s patches serve as the immune system of the gut, where foods and potentially pathogens are first absorbed in the body. Studies have been reported on the activation of the systemic immune system through the activation of the intestinal immune system. CCP- 0’s effect on the intestinal immune system demonstrated that granulocyte-macrophage colony-stimulating factor production increased significantly, and bone-marrow-cell proliferation increased by more than 40% (Shin, 2017).
Melanoidins are what make coffee (and other foods) brown when roasted, baked or toasted. They are formed during the Maillard reaction, when sugars and amino acids combine at high temperatures and low water activity. They may be considered bioactive compounds (Bekedam, E.K., et. al., 2008). The more intermediate and high-molecular-weight melanoidins are produced the darker we roast the coffee.
Coffee melanoidins may act as soluble fiber enhancing immune-stimulating properties and contributing significantly to reducing the risk of colon cancer (Vitaglione, 2012; Moreira, 2015; Fogliano, 2011). This likely happens by decreasing colon inflammation through improved microbiota balance (prebiotic effect) and by increasing the elimination rate of carcinogens through higher colon motility (urge to use the bathroom). In other words, melanoidins can function as an antioxidant dietary fiber and act like a ‘sponge’ for free radicals in the gut.
Coffee melanoidins may act to promote the growth of a beneficial colon microbiota, affecting inflammatory pathways in the colon and consequently in the liver. These appear to activate their scavenging properties gradually, and some showed that the radical scavenging ability of coffee melanoidins was higher in the dark-roasted coffee (Bekedam, 2008).
Putting it All Together
Basic Recipe for Cold Brew Coffee
Goal: To extract as many pleasing flavors as possible (you decide!) from the ground coffee beans into the cup and create a balanced and delicious beverage.
How: There are numerous methods of preparing cold brew, but they all come down to immersing coffee in cold water over a certain amount of time, depending on how important the extraction of different compounds is for you. For maximum antioxidant extraction, the research we presented indicates in general that about 24 hours is good.
Below is a basic recipe, which hopefully you can apply to any cold brew device. Using a French press most easily demonstrates the basic principles of cold brewing that can be applied to other methods.
- Device: French press with about 1.5 liter capacity
- Filter: Stainless steel mesh included with French press (some presses have filters with other materials).
- Coffee: Medium-coarsely ground. 125g (4.5 oz or approximately 1.5 measuring cups firmly packed coffee grounds).
- Water: 1000ml (appx. 32 oz) — cold or room temperature, clean.
- For a more concentrated cold brew, try 100g of coffee with 500 ml of water.
- For a less concentrated brew, try 100g coffee with 1000 ml of water.
- Time: 24 hours (give or take 6 hours)
- Grind the coffee fresh just before mixing the coffee and water together in the carafe. Make sure all the grounds are saturated with water.
- The grounds will have risen to the top of the carafe, which is called the “crust”. Stir again after 5 minutes using your spoon to break the crust and submerge the grounds.
- Place the French press plunger in the carafe and push it down slightly below the surface to keep the grounds submerged. Let the cover of the press close the top of the carafe, so that no foreign odors or particles get into the cold brew.
- Place the French press in the refrigerator for at least 8 hours, but more like 16-24 hours.
- Filter the cold brew concentrate by slowly pushing down on the plunger. The coarser grinds will act like a net for the finer particles, most of which would have likely fallen to the bottom of the flask anyway by this time.
- If you are watching your cholesterol, you may want to do an additional step of filtering your coffee through a funnel with a paper filter. This will trap much of the oils that have been shown to be of concern for those with high cholesterol.
- Create your final beverage by diluting with water or ice and combining it with whatever other ingredients you like.
- Try the cold brew without any additives first. See what flavors emerge and then decide what else to put with it. You may decide you do not need any sweetener, if you normally add it.
- Studies indicate that adding dairy milk products reduce the bioavailability of the CGA (Farah, 2006).
- Store the cold brew concentrate in the fridge for up to 10 days. Mark the expiration date yourself with masking tape and a marker.
- When the cold brew is finished, thoroughly clean the French press carafe, filter (take it apart), and lid, making sure each tiny nook and cranny has been sanitized. Air dry and store in a hygienic area.
Chart of Brewing Variables for Cold Brew Coffee
|Variables and Choices for Cold Brewing|
|Quality of the water used (no chlorine, some mineral content, but not too much)||Clean/fresh, odor free, clear color. NO chlorine. |
Essentially, look for water with some mineral content. The coffee flavors seem to be brought out more with total dissolved minerals between 75 - 250 mg/l (calcium 17 - 85 mg/l, sodium around 10 m/l), and pH between 6.5 - 7.5.
Distilled water is not optimal.
|“Spring water” is good.
Pure, chemical-free water is good to use.
|Type of brewing device (and filter method)||Glass, metal or other non-breakable material for the flask. |
Filters could be metal, cloth or paper. Paper filters remove much of the natural coffee oils. This is preferable for people watching their cholesterol, but the oils have some great health benefits, particularly for the liver.
How much space is in your fridge? Shelf height?
|You can cold brew with any pitcher or jar that has a lid (keeps odors and microscopic stuff floating around your fridge out of the coffee). Consider how you will filter or sieve from a jar. You can use a pour-over coffee maker or a Chemex with a paper filter, to strain out the grounds.
You can re-purpose a French press.
Various cold brew devices are on the market. Some have filters that sit in the center of the flask. Others are like French presses.
|Ratio of coffee to water used||How strong do you normally like your coffee? Will you be adding ice? Will you use the cold coffee as an ingredient among others? If so, how prominent do you want the coffee flavor? |
You’ll need more ground coffee for cold brew than hot brew.
It really depends how concentrated you want it.
|The ratios vary widely. Adjust to taste! Start around 1:4 or 1:5, meaning 1 packed cup of ground coffee to 4 or 5 cups of water. Or 100 g for 500 ml water.
I am happy with 100 g of Purity Dark Roast coffee for 1000 ml of water, which is 1:10!
|Appropriate grind size||Use a medium-coarse grind, similar to coarse salt or ½ the particle size of decorator’s sugar.
Too fine coffee will taste over-extracted and make the coffee “muddy”.
|Temperature of the water||Room temperature water or below. |
Continue the brew in the fridge.
|Between 34º-80ºF (1.1º-26.7ºC)|
|Length of brew time||Which health benefits do you look for? The longer the coffee steeps, the more it will extract, although some research showed that 8 hours was sufficient, we can be fairly certain that by 30 hours the coffee will have reached equilibrium and no further compounds will be released.||Experiment. Try 8 hours. Try 12 hours. Try 18 to 30 hours and try to observe how the cold brew effects your body and mind. Do you focus better with coffee brewed for 24 hours?|
- Almeida A, Naghetini C., Santos V, Glória M. 2004. In Vitro antimicrobial activity of coffee extracts on Streptococcus mutans. In 20th International Conference on Coffee Science, Bangalore, India. Proceedings of ASIC Conferences. pp 242-248.
- Almeida, A., Farah, A. Silva, D., Nunan, E. Glória, B. 2006. Antibacterial Activity of Coffee Extracts and Selected Coffee Chemical Compounds against Enterobacteria. J. Agric. Food Chem., 54, 8738-8743.
- Baranowski J., Nagel C. 1982. Inhibition of Pseudomonas fluorescens by hydroxycinnamic acids and their alkyl esters. J. Food Sci., 47, 1587-1589.
- Bekedam E, Loots M, Schols H, Van Boekel M, Smit G 2008. Roasting Effects on Formation Mechanisms of Coffee Brew Melanoidins. J. Agric. Food Chem. 2008, 56, 16, 7138–7145
- Cain D, O’Koren E, Kan M, Womble M, Sempowski G, Hopper K, Gunn M, Kelsoe G. 2013. Identification of a Tissue-Specific, C/EBPb-Dependent Pathway of Differentiation for Murine Peritoneal Macrophages. www.jimmunol.org/content/early/2013/09/27/jimmunol.1300581.
- Cordoba N, Pataquiva L, Osorio C, Moreno F, Ruiz RY. 2019. Effect of grinding, extraction time and type of coffee on the physicochemical and flavour characteristics of cold brew coffee. www.nature.com/scientificreports. 9:8440
- Daeschel M, Armbrust N, Vieru C. 2017. Survival of non-spore forming foodborne pathogens in cold brewed coffee. https://mountaincity.com/images/Cold-Brew-Study.pdf, https://www.mintel.com/blog/drink-market-news/the-strength-of-cold-brew, https://www.naturalgrocers.com/product-recall/voluntary-recall-califia-farmsmocha-cold-brew-coffee
- Daglia M., Cuzzoni MT, Dacarro C. 1994. Antibacterial Activity of coffee. J. Agric. Food Chem., 42, 2270-2277.
- Farah A. editor (2019). Coffee: Production, Quality and Chemistry. Royal Society of Chemistry.
- Farah A. editor (2019). Coffee: Consumption and Health Implications. Royal Society of Chemistry.
- Farah A. (2018) Nutritional and health effects of coffee. Lashermes P. (ed.), Achieving sustainable cultivation of coffee, Burleigh Dodds Science Publishing, Cambridge, UK., 1-31.
- Farah A. (2013). Coffee: Emerging Health Effects and Disease Prevention. IFTPress, Ch. 2, 22-58.
- Farah A., de Paulis T., Moreira D.P., Trugo C., Martin P. (2006). Chlorogenic Acids and Lactones in Regular and Water-Decaffeinated Arabica Coffees. Agricultural and Food Chemistry, 54, 374-381.
- Farah A., de Paulis T., Trugo C., Martin P. (2005). Effect of Roasting on the Formation of Chlorogenic Acid Lactones in Coffee. Agricultural and Food Chemistry, 53, 1505-1513.
- Fogliano ,V., and Morales F. J. (2011). Estimation of dietary intake of melanoidins from coffee and bread. Food Funct. 2, 117–123.
- Fuller M. Rao, N. 2017. The Effect of Time, Roasting Temperature, and Grind Size on Caffeine and Chlorogenic Acid Concentrations in Cold Brew Coffee. www.nature.com/scientificreports. 7:17979.
- Garrote, G., Cruz, J., Moure, A., Dominguez, H., Parajo, J. 2004. Antioxidant activity of byproducts from the hydrolytic processing of selected lignocellulosic materials. Trends Food Sci. Technol., 15, 191-200.
- Lee T, Kempthorne R, Hardy J. 1992. Compositional changes in brewed coffee as a function of brewing time. J Food Sci 57(6):1417-9.
- Lopez J. 2020. Cold Brew Coffee Regulations and Policies. New York State Department of Agriculture & Markets, Division of Food Safety & Inspection, International Food Protection Training Institute (IFPTI), Cohort VIII.
- Morrisey A. 2019. The Effect of Grind Size and Brew Time upon Antioxidant Potential, Sensory Profile, and Consumer Likability of Cold Brew Coffee. Montclair State University Digital Commons. Theses, Dissertations and Culminating Projects.
- Moreira A. S. P., Nunes F. M., Domingues M. R., and Coimbra M. A., (2012). Coffee melanoidins: structure, mechanisms of formation and potential health impacts. Food Funct 3, 903–915.
- Shin K-W. 2017. The Chemical Characteristics and Immune-Modulating Activity of Polysaccharides Isolated from Cold-Brew Coffee. Prev. Nutr. Food Sci. 22(2):100-106.
- Vitaglione P., Morisco F., Mazzone G., Amoruso D. C., Ribecco M. T., Romano A., Fogliano V., Caporaso N., and D’Argenio G. (2010). Coffee reduces liver damage in a rat model of steatohepatitis: the underlying mechanisms and the role of polyphenols and melanoidins. Hepatology, 52, 1652–1661.
- Zuniga M. (2016, May 16). Cold brew: Category or craze? Re;co: The Specialty Coffee