foods Review The Flavor Chemistry of Fortified Wines—A Comprehensive Approach Teresa Abreu 1, Rosa Perestrelo 1 , Matteo Bordiga 2 , Monica Locatelli 2 , Jean Daniel Coïsson 2 and José S. Câmara 1,3,* 1 CQM–Centro de Química da Madeira, Universidade da Madeira, Campus Universitário da Penteada, 9020-105 Funchal, Portugal; [email protected] (T.A.); [email protected] (R.P.) 2 Dipartimento di Scienze del Farmaco, Università degli Studi del Piemonte Orientale “A. Avogadro”, Largo Donegani 2, 28100 Novara, Italy; [email protected] (M.B.); [email protected] (M.L.); [email protected] (J.D.C.) 3 Departamento de Química, Faculdade de Ciências Exatas e Engenharia, Campus da Penteada, Universidade da Madeira, 9020-105 Funchal, Portugal * Correspondence: [email protected]; Tel.: +351-(291)-705112 Abstract: For centuries, wine has had a fundamental role in the culture and habits of different civilizations. Amongst numerous wine types that involve specific winemaking processes, fortified wines possess an added value and are greatly honored worldwide. This review comprises the description of the most important characteristics of the main worldwide fortified wines—Madeira, Port, Sherry, Muscat, and Vermouth—structured in three parts. The first part briefly describes the chemistry of wine flavor, the origin of typical aroma (primary, secondary and tertiary), and the influencing parameters during the winemaking process. The second part describes some specificities of worldwide fortified wine, highlighting the volatile composition with particular emphasis on aroma compounds. The third part reports the volatile composition of the most important fortified wines, including the principal characteristics, vinification process, the evolution of volatile organic Citation: Abreu, T.; Perestrelo, R.; compounds (VOCs) during the aging processes, and the most important odor descriptors. Given Bordiga, M.; Locatelli, M.; Daniel the worldwide popularity and the economic relevance of fortified wines, much research should be Coïsson, J.; Câmara, J.S. The Flavor Chemistry of Fortified Wines—A done to better understand accurately the reactions and mechanisms that occur in different stages of Comprehensive Approach. Foods winemaking, mainly during the oxidative and thermal aging. 2021, 10, 1239. https://doi.org/ Keywords: flavor; aroma origin; fortified wines; enology; vinification process; aging; odor descrip- Academic Editor: Panagiotis Kandylis tors; Madeira wines Received: 17 March 2021 Accepted: 26 May 2021 Published: 29 May 2021 1. A Short Introduction about Wine Flavor Chemistry Chemically, wine is a fascinating and very complex matrix constituted by several Publisher’s Note: MDPI stays neutral hundreds of chemical compounds/groups—water, ethanol, glycerol, organic acids, car- with regard to jurisdictional claims in bohydrates, and, to a minor extent, terpenoids, pyrazines, higher alcohols, ethyl esters, published maps and institutional affil- fatty acids, nitrogenous compounds, sulphur compounds, furanic compounds, among iations. others. These chemical groups were found in a broad range of concentrations (from a few mg/L to ng/L) and presenting different polarities and volatilities [1–4]. Table1 shows the main volatile organic compounds (VOCs) found in wines. Some VOCs are responsible for the singular aromatic characteristics of some wine types. It should be mentioned that the Copyright: © 2021 by the authors. most pleasant wines hardly have precise and simple to identify aromas; rather, they have Licensee MDPI, Basel, Switzerland. complex aromatic aroma descriptors in which some fruit and floral perception is crucial, This article is an open access article along with other spicy, woody, and/or toast notes. It should also be pointed out that the distributed under the terms and lack of aromatic faults or variations is also a constant and vital factor of quality [1,5]. conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 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