beverages Review Beer Polyphenols—Bitterness, Astringency, and Off-Flavors Kristina Habschied 1,* , Iztok Jože Košir 2 , Vinko Krstanovi´c 1 , Goran Kumri´c 3 and Krešimir Mastanjevi´c 1 1 Faculty of Food Technology, Josip Juraj Strossmayer University of Osijek, F. Kuhaˇca20, 31000 Osijek, Croatia; [email protected] (V.K.); [email protected] (K.M.) 2 Slovenian Institute of Hop Research and Brewing, Cesta Žalskega Tabora 2, 3310 Žalec, Slovenia; [email protected] 3 European Food Safety Authority, Via Carlo Magno 1a, 43126 Parma, Italy; [email protected] * Correspondence: [email protected]; Tel.: +385-31-224-300 Abstract: The acceptance of beer among consumers is most influenced by the taste and aroma. Polyphenols are widely responsible for both. Whereas polyphenols do not always result in a positive flavor and taste, they can surely impart certain off-flavors, which will be mentioned in this paper. However, the aftertaste is an important component of the beer-tasting experience and acceptance. The aftertaste, including astringency, may largely influence consumers’ consumption preference and behavior. Bitterness is one of the main, desirable characteristics of beer, but to an untrained consumer, it can often be mistaken with astringency. This review aims to describe the differences between these two properties. Both attributes derive from the same beer components, polyphenols from barley and hop, but there is a distinctive difference between them. To understand the complexity of bitterness and astringency, polyphenols behavior, characteristics, and stability during the brewing process are also described in this review. Citation: Habschied, K.; Košir, I.J.; Keywords: bitterness; beer; aftertaste; off-flavor Krstanovi´c,V.; Kumri´c,G.; Mastanjevi´c,K. Beer Polyphenols— Bitterness, Astringency, and Off-Flavors. Beverages 2021, 7, 38. 1. Introduction https://doi.org/10.3390/ Flavor stability is, besides colloidal stability, one of the most important indicators beverages7020038 of beer quality. The two properties are narrowly connected since the colloidal stability purports the polyphenol removal, a big factor in flavor stability [1]. Some types of beer Academic Editors: Luis F. Guido (i.e., Indian Pale Ale) are bound to contain strong hoppy notes and bitterness originating and Pavel Dostálek from polyphenols in hops or barley. In some types of beer, such as lagers, the manifestation of these properties is undesirable. However, the emergence of undesirable notes can be a Received: 5 May 2021 result of a faulty lead brewing process, whether due to the over-dosage of hop (acids), low Accepted: 8 June 2021 Published: 11 June 2021 temperatures while dry hopping, polyphenols, or simply staling. The ongoing craft beer boom has aimed to present different types of beer to the broader public, and this includes Publisher’s Note: MDPI stays neutral hoppy and bitter beers (mostly ales) that differ from the industrial lagers by increased with regard to jurisdictional claims in bitterness [2]. Other important beer characteristics, such as astringency, body, and fullness, published maps and institutional affil- are directly influenced by polyphenols [3]. iations. As such, polyphenols can provide both bitterness and astringency, depending on their degree of isomerization [4]. The consumers’ perception of bitterness depends on different factors and is very complex. The range of molecules that elicit bitter responses is very wide [5,6]; for example, the reactivity of flavanols with metal ions and molecular oxygen results in flavanol polymers. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Astringency, on the other hand, is much easier to explain. It is described as a mouthfeel This article is an open access article characterized by a drying, puckering, or rough sensation across the oral cavity, especially distributed under the terms and on the tongue [7]. It occurs when large molecular weight polyphenols react with proline- conditions of the Creative Commons rich proteins found in saliva. Upon their interaction, they precipitate onto the surface of Attribution (CC BY) license (https:// the mouth, which leads to the feeling of a coating dryness [8]. creativecommons.org/licenses/by/ Beer is comprised of several hundred compounds affecting its aroma and taste. The 4.0/). terminology for the determination of beer flavor is complex and includes dynamic inter- Beverages 2021, 7, 38. https://doi.org/10.3390/beverages7020038 https://www.mdpi.com/journal/beverages Beverages 2021, 7, x FOR PEER REVIEW 2 of 15 Beverages 2021, 7, x FOR PEER REVIEW 2 of 15 Beverages 2021, 7, 38 2 of 14 terminology for the determination of beer flavor is complex and includes dynamic inter- actionsterminology between thefor thesenses determination [9]. As reported of beer in flavora review is complex by Baert and et al.includes [9], “flavor dynamic is the inter- actions between the senses [9]. As reported in a review by Baert et al. [9], “flavor is the sum actionsof perceptions between resulting the senses from [9]. stimulation As reported of inthe a reviewsense ends by Baertthat are et al.grouped [9], “flavor at the is the sum of perceptions resulting from stimulation of the sense ends that are grouped at the entrancesum of of the perceptions alimentary resulting and respiratory from stimulation tracts” [10,11], of the and sense flavor ends is that comprised are grouped of four at the entrance of the alimentary and respiratory tracts” [10,11], and flavor is comprised of four differententrance components: of the alimentary odor, aroma, and respiratory taste, and tracts”mouthfeel. [10,11 By], anddefinition, flavor isthe comprised odor is the of four different components: odor, aroma, taste, and mouthfeel. 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