ResultsBackground & Hypothesis

Results

References

Results

International Bitterness Units and Perceived Bitterness

Michael Kamnikar, Kimberly Korbe, Stephan SiegleDepartment of Food Science and Human Nutrition

Methods

Test 2 vs. Test 3:A comparison of these two tests showed reduced bitterness intensities for all three beers that were used. However, the high p-values that were calculated from the data indicate that there was no significant changes for beers B and E. The p-value for beer D was 0.057. This means that the drop in bitterness intensities for beer D showed no significance, however, it may have a statistical significance if further testing was done. This is based on how close it was to the 0.05 limit for statistical significance.

Conclusions

Test 1:This test was used to see if the sensory group would correctly identify bitterness intensities of beers ranging from 60 IBUs to 80 IBUs. The results indicate that, as a whole, the sensory panel ranked the three beers sampled with increasing bitterness intensities. This mirrors the trend of bitterness units, both claimed and measured in the beers used for test 1.

Test 2:Test 2 was done with beers that had a more narrow range of IBUs (61-69 measured). This test showed a more diverse range of scores and the final intensities were not consistent with the actual IBUs. This indicates that olfactory variations, such as hop aromas, and visual differences, like color, influence how the test group perceived the bitterness intensities of each beer.

Spectrophotometry indicated that beer A, B and C had measured IBUs which were very close to those stated on the websites of the breweries. However beer D was nearly 9 IBUs lower than what was stated, while beer E was almost 13 IBUs higher that what was stated. This actually narrowed the range of IBUs of the beers used for test 2 and 3 to less than 9 IBUs from lowest to highest.

Test 3:This test indicated a diminished variation between the samples used for test 2 when participants had their noses plugged. All three samples had intensity values lower than what they were scored in the previous test. This showed that without the olfactory sense, the bitterness intensities were not only lower, but were also closer to each other in the range of intensities.

Special Thanks to our mentor Ali Hamm for her guidance and to Justin Alexander with New Belgium Brewing Company for his assistance in measuring international bitterness units of all beers used in this study.

The intensities ranged significantly between the participants in test 1. However, the progression of bitterness profiled the IBUs in the beers. The variation of intensity could be reduced by having a reference sample with a specific value for its bitterness. Also, the test panel were students from the “Sensory of Fermented Foods” class rather than a trained panel. Due to time restrictions, and limitations on funding, we were not able to work with the panel to standardize the intensity ratings. A comparison of test 2 and 3 shows that as the nose is plugged the bitterness perception was less distinguishable from one beer to another. Although the p-values indicated no significance for beers B and E, sample D may provide relevance to the idea that IBUs do not always represent the perceived intensity of bitterness in a beer. Also, we conducted all three tests within a 30 minute timeframe which might have led to sensory fatigue for some participants. We feel that it would be a good idea to perform the sensory evaluation again after the participants have been properly trained on scoring thru samples by using a reference. This experiment was done with a variety of IPAs from Colorado breweries purchased at a local liquor store. This created many variables which could affect the perception of bitterness.

• Sample population was 20 students in the Sensory of Fermented Foods class.• All beer samples were from local Colorado breweries.• Test 1 had the 60 IBU beer, a 70 IBU beer and an 80 IBU beer.• Test 2 had both 70 IBU beers, and the 55 IBU beer.• Test 3 was the same as test 2 but was conducted with the nose plugged to

ensure no retro nasal could be detected.• Each beer was given 2 different 3 digit codes for randomization (5).• Each sample was analyzed using the ASBC beer method at New Belgium

Brewing Company (6).

The world of craft brewing is expanding, so is the abundance of India Pale Ales (IPAs) on the market. An IPA is a style of beer that uses a lot of hops in order to increase bitterness. The level of bitterness is determined by the amount of International Bitterness Units (IBUs) in the beer. IBUs are calculated when acidified beers extracted with iso-octane and the optical density of the extract is determined in a spectrophotometer (1). The value is then converted numerically into IBUs. The more IBUs that a beer has, the more bitter it should be. However, there has been some controversy towards IBUs because of the way people perceive bitterness. For example, in one study, beers high in polyphenol and hop acid contents were perceived as having ‘harsh’ and ‘progressive’ bitterness, whilst beers that had evidently been conventionally hopped were ‘sharp’ and ‘instant’ in their bitterness (2). It should also be noted that within affective testing participants unexpectedly perceived the lighter yellow beer as significantly more bitter than the dark black beer (3). Bitterness perception may be influenced by retro nasal olfaction. Measuring possible effects of taste on retro nasal olfaction is important because in the field of food science, the study of interactions between tastes and odors has focused on how tastes can increase the perception of the volatile components of foods (4).

This study aims to explore how people perceive different levels of bitterness in beers. It tested whether olfactory senses play a role in perceived bitterness. People should be able to rate IPAs based on their IBUs. If retro nasal is removed from the equation, this ability should be affected based on the lack of the retro nasal component.

(1) Howard, G. (1968). Estimation of the bitterness of beer. Journal of the Institute of Brewing, 74, 249-251. Retrieved April 13.(2) Oladokun, O., Tarrega, A., James, S., Smart, K., Hort, J., & Cook, D. (2016). The impact of hop bitter acid and polyphenol profiles on the perceived bitterness of beer. Food Chemistry, 205, 212-220. Retrieved March 29, 2016.(3) Spearot, J. Influence of Beer Color on Perception of Bitterness. Drexel University. Retrieved March 28, 2016.(4) Green, B., Nachtigal, D., Hammond, S., Lim, J. (2011). Enhancement of retronasal odors by taste. Chemical Senses, 37 (1), 77-86. Retrieved April 15.(5) Meilgaard, M. C., Civille, G. V., & Carr, B. T. (2016). Sensory evaluation techniques. Boca Raton, FL: CRC Press. Retrieved April 15.(6)  "ASBC Methods of Analysis – Beer-23: Beer Bitterness." ASBC Methods of Analysis – Beer-23: Beer Bitterness. American Society of Brewing Chemists, n.d. Web. 20 Apr. 2016.

Acknowledgements