Caffeine Content In 
Ready-To-Drink 
Coffee Products

Ready-to-drink coffee products are more popular than ever, yet little to no regulatory pressure is placed on RTD coffee manufacturers to deliver on caffeine promises. Eight (8) single-strength and five (5) coffee concentrates were purchased from local grocery stores and evaluated for caffeine content using HPLC-DAD. Other physical characteristics that are thought to be associated with brewed coffee strength were also measured, such as visual color  and refractive index (°Brix). The results suggest that coffee manufacturers are exceeding the expected quantity of caffeine, and that both single-strength RTD and 2X concentrated coffee products vary widely in caffeine content. Further, physical parameters such as °Brix were  poor predictors of caffeine content. This presents an opportunity for the coffee industry and researchers to improve caffeine claim accuracy and engender trust from coffee consumers.

Coffee is one of the most widely used and culturally relevant CPG for boosting energy 1. Consumers have a myriad of plant-based options for energy—Kava kava, maca root, taurine, ginseng, and mushroom extracts, to name a few—yet, none of these have managed to make a dent in coffee sales or consumption. One of the most popular and growing sub-segments of the coffee market are RTD options, from canned lattes to gallons of prepared cold brew. 


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RTD coffees can be prepared using a myriad of ingredients and process parameters—including temperature, time, and pressure—all which may affect the end total of caffeine present and the sensory “strength” of the brew. However, due to their classification as “food” by governing bodies, coffee products have experienced little to no regulatory pressure to ensure caffeine dosing accuracy in coffee-containing foods. That may be why many brands opt for the most cost-effective option for dose estimation: measurement of refractive indices (Brix), which is subsequently converted using a 0.85 factor to estimate total dissolved solids (TDS). Brix has been previously reported to be linearly correlated with TDS, sensory attributes and caffeine 2. Given the reported linear association with these defining attributes of coffee, °Brix, or the simple TDS conversion, is commonly utilized as a quality control metric for “strength” in RTD brews.


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For many novel products containing energy-promoting botanicals, dosing can be a major challenge both during formulation and manufacturing. Process parameters must be controlled more robustly than in ordinary food 
to ensure homogeneity across units. Given the widespread prominence of mislabeling in both caffeine-containing 
3,4 and similar botanical-containing products 5,6, the question of whether °Brix is a reliable, practical metric
for estimation of coffee brew caffeine content merits re-evaluation. The present investigation aims to evaluate 
whether claimed or assumed caffeine values in brewed RTD coffees are consistent with measured values. Cold brew 
single-strength and concentrated RTD coffees were selected specifically for the relative simplicity of the matrix compared 
to other RTD coffee products. Further, the study aimed to assess refractive index as an indicator of caffeine concentration.

Two types of products were considered for this investigation: RTD cold brew beverages with no added ingredients and 
cold brew concentrates with no added ingredients. Five (5) concentrates and eight (8) single-strength RTD cold brew products were purchased for evaluation from local grocery stores. In total, thirteen (13) coffee products cold brew coffee products were included in the study. All samples were stored refrigerated according to manufacturer recommendations prior to analysis. 


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Caffeine was quantified using HPLC with a diode array detector. Integrated peak area was compared against a standard caffeine dilution series to establish caffeine content (mg/ml). Using the serving sizes provided on the nutrition facts label 
for each product, per-serving caffeine content (in mg) was calculated.

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In addition to caffeine quantification, several physical parameters were also analyzed. °Brix was measured using room temperature coffee aliquots and a Milwaukee digital refractometer. Color was analyzed visually using a standard 1cm diameter cuvette and the Lovibond standard reference method for brownness 7 .

Data were analyzed using Pearson linear regression and t-tests using XLSTAT analysis software. A significance threshold of p<0.05 was used throughout the study. Single-strength and concentrated coffees were analyzed separately unless otherwise stated.  


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Not all RTD coffee products included a label claim describing the caffeine per serving, leaving consumers  to assume caffeine content. For sampled products in this study where no caffeine claim was made, the commonly  referenced value of 95mg caffeine per 8 fl oz serving of coffee was used as the “assumed” claim, as this is what a consumer would realistically use to estimate caffeine content. Two of the eight (2/8) single-strength brands and four of the five (4/5) concentrates did not make caffeine claims on the package.

Of the eight (8) single-strength RTD cold brew brands evaluated, six (6) were outside of 10% of  the claimed caffeine value. Of these six, caffeine content ranged from 34.18% to 150% of the  claimed value. Two (2) brands were within 10% of the claimed caffeine value. Table 1 provides a summary of the measured and claimed values for each of the brands evaluated. Figure 1 illustrates actual caffeine content per serving compared to the claimed or assumed caffeine content of the product.

Of the five (5) cold brew concentrate brands, none were with 10% of the claimed caffeine value. The brands ranged from 63% to 182% of the claimed caffeine value. Table 2 provides a summary of the measured and claimed values for each of the brands evaluated.

Both caffeine and °Brix were significantly lower for single-strength (0.52mg/ml, 1.69°Bx) compared to concentrated cold brews (1.32mg/ml, 3.14°Bx) (p<0.0001).

The data suggests °Brix is a useful measurement to distinguish single-strength from concentrates (all acclaimed 2x strength in this study), but not at all suitable for estimating caffeine within strength. The usage of °Brix as a metric to estimate brew “doneness” may partially explain the average gap of 25% between claimed caffeine content and measured caffeine content. Inaccurate dosing, especially in cases where the dose is much higher than the expected dose, may contribute to the association between adverse health events and caffeine 8.

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The strength of the relationship between °Brix and caffeine in single-strength RTD cold brew was as low as a simple evaluation of brew color (r=0.32 vs. =0.29, respectively), suggesting that simply looking at the beverage may be as effective as measuring °Brix when comes to estimating caffeine concentration.

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Unfortunately, there are few alternatives for estimating strength of RTD coffee during manufacturing. RTD coffee manufacturers must consider whether the risk of selling over-caffeinated products outweigh the costs of accurate caffeine testing by HPLC. A relatively small investment in development of process and product-specific caffeine concentration models may result in more accurate labeling until a more robust bench-top method is developed.

References

1. Samoggia, A.; Riedel, B. Coffee Consumption and Purchasing Behavior Review: Insights for Further Research. Appetite 2018, 129, 70–81. https://doi.org/10.1016/j.appet.2018.07.002.
2. Gloess, A. N.; Schönbächler, B.; Klopprogge, B.; DAmbrosio, L.; Chatelain, K.; Bongartz, A.; Strittmatter, A.; Rast, M.; Yeretzian, C. Comparison of Nine Common Coffee Extraction Methods: Instrumental and Sensory Analysis. Eur. Food Res. Technol. 2013, 236, 607–627.
3. Desbrow, B.; Hall, S.; O’Connor, H.; Slater, G.; Barnes, K.; Grant, G. Caffeine Content of Pre-Workout Supplements Commonly Used by Australian Consumers. Drug Test. Anal. 2019, 11 (3), 523–529. https://doi.org/10.1002/dta.2501.
4. Cohen, P. A.; Attipoe, S.; Travis, J.; Stevens, M.; Deuster, P. Caffeine Content of Dietary Supplements Consumed on Military Bases. JAMA Intern. Med. 2013, 173 (7), 592–594.
5. Venhuis, B. J.; Zwaagstra, M. E.; Keizers, P. H. J.; de Kaste, D. Dose-to-Dose Variations with Single Packages of Counterfeit Medicines and Adulterated Dietary Supplements as a Potential Source of False Negatives and Inaccurate Health Risk Assessments. J. Pharm. Biomed. Anal. 2014, 89, 158–165. https://doi.org/10.1016/j.jpba.2013.10.038.
6. Larimore, W. L.; O’Mathúna, D. P. Quality Assessment Programs for Dietary Supplements. Ann. Pharmacother. 2003, 37 (6), 893–898. https://doi.org/10.1345/aph.1D031.
7. Lovibond, J. W. On the Scientific Measurement of Colour in Beer. J. Fed. Inst. Brew. 1897, 3 (5), 405–429.
8. Jagim, A. R.; Harty, P. S.; Fischer, K. M.; Kerksick, C. M.; Erickson, J. L. Adverse Events Reported to the United States Food and Drug Administration Related to Caffeine-Containing Products. Mayo Clin. Proc. 2020, 95 (8), 1594–1603. https://doi.org/10.1016/j.mayocp.2020.02.033.