Influence of different brewing techniques on iso-α-acid content and sensory properties of beer

Abstract

Beer is produced by fermenting hopped wort with yeast. The raw materials are water, grain, hop and yeast. One source of taste and aroma in beer is hop, which is typically added during boiling. One reaction during boiling is that α-acid from hop is converted to iso-α-acid, which makes the beer bitterer. Iso-α-acid is responsible for bitterness in beer, but it might also be reacted to other bitter molecules, e.g. rho-iso-α (70% bitterness of iso-α), tetrahydro-iso-α (100-110% bitterness of iso-α). Thus it is interesting to investigate if the iso-α-acid amount is more efficient for describing the overall bitterness than traditional IBU (International Bitterness Unit) measurement. Furthermore, other compounds from hop are also extracted into the wort during boiling, they go through chemical reactions and the reaction products contribute to the taste of beer. Thus different brewing techniques bring various sensory properties to beer. And in this sense, it is interesting to investigate how different brewing techniques influence sensory properties and the iso-α-acid amount in beer.
The traditional way to quantify iso-α-acid is through liquid extraction by isooctane and to measure the absorbance value at 275nm (maximum absorption wavelength). The overall absorbance roughly represents the iso-α-acid amount and IBU is defined as the absorbance value*50. However, other compounds will be extracted and they will contribute to the overall absorbance. One state-of-the-art analysis is HPLC-UV quantification, which is robust and precise and the pretreatment before HPLC is usually chosen as solid phase extraction (SPE) or liquid liquid extraction (LLE).
In this study, four pale ales were produced with different brewing techniques with the same estimated bitterness. The concentration of iso-α-acid amount was quantified with modified HPLC pretreatment, IBUs were measured and α-acid utilizations were calculated. The purpose of keeping the same bitterness is to investigate how the iso-α-acid amount and IBU change within the same bitterness. Sensory properties were evaluated through a triangle test and a preference test. The triangle test aims to investigate whether bitterness is the same as expected, meanwhile the preference test aims at figuring out which brewing techniques consumers prefer most, as well as its connection with iso-α-acid amount.
It was concluded that brewed ales had the same bitterness as expected, but the iso-α-acid amount varied. The best pretreatment for HPLC-UV is LLE of acidified beer (1mL 12M HCl) with isooctane, which is followed by solvent removal under vacuum. IBU is more efficient for describing overall bitterness than the iso-α-acid amount. The brewing technique “all late hopping” is the most preferable, which is has the lowest α-acid utilization.

Popular Abstract

The raw materials for beer production are water, grain, hop and yeast. It is produced by mashing and boiling milled malt with added hop, which is followed by yeast fermentation in cool wort. Different brewing techniques bring various flavors to beer. Early addition of hop gives more bitterness and less aroma, and late hopping results in more aroma and less bitterness. The major group of bitter molecules derived from hop is collectively called α-acid, which is converted to iso-α-acid (more bitterness) during boiling. It has been reported that iso-α-acid is the main bitter molecules for beer.
It is interesting to investigate how brewing techniques influence sensory properties and iso-α-acid amount in beer. Besides, it is interesting to investigate whether iso-α-acid amount could describe the overall bitterness more efficiently than traditional IBU (International Bitterness Unit) measurement. One easy way to measure iso-α-acid amount is absorbance value from liquid extraction under its maximum absorption wavelength and IBU is defined as absorbance value*50. The main disadvantage is that other compounds are also extracted and contribute to final results. One state-of-the-art way is to quantify iso-α-acid with HPLC-UV, which is more robust and precise. However, it is demanding on material, equipment and pre-trial experiment.
In this study, four pale ales were produced by different brewing techniques but with the same bitterness expectation. Recipes and bitterness were formulated from BeerSmith software. IBUs were measured and α-acid utilizations were calculated in each beer. This aim was to investigate how iso-α-acid amount and IBU vary within the same bitterness beers. Besides, iso-α-acid amount was quantified with modified LLE pretreatment in order to see the overall bitterness is more correspondent to which value. Sensory properties were investigated by two sensory analyses. One triangle test was designed to investigate taste differences, i.e. whether the bitterness are the same as expected. Another preference test was performed to see which brewing technique consumers prefer most, in order to see whether there is a correlation between the iso-α-acid amount and brewing technique.

• author: Lu, Yi
• supervisor: Lars Nilsson
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLGM01 20151
• year: 2015
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: beer brewing, hop, iso-α-acid, food technology, livsmedelsteknologi
• language: English
• id: 8001160
• date added to LUP: 2015-09-30 11:02:28
• date last changed: 2015-09-30 11:02:28