# Volatile Composition of Fortification Grape Spirit and Port Wine: Where Do We Stand?
## 3 Port Wine's Production: The Relevance of the Fortification Step
Continuous stills consist in column stills, usually up to three, in which the steam is separated by means of reflux of the descending liquid and is carried out to the following plates where it is again concentrated to the desired alcoholic percentage [43]. Considering the capacity of extracting a higher ethanol concentration, column stills are more cost effective than pot stills, with the latter technique being more laborious, time consuming, and less efficient energetically [44]. Both types of distillers allow the separation of the different fractions, commonly referred to as \"cuts\". Compounds with higher volatility, such as acetaldehyde, acetal and ethyl acetate, are present in the \"head cut\". Conversely, the \"tail cut\" contains volatile compounds with higher boiling points, such as ethyl esters of long chain fatty acids. Both fractions include undesirable volatile compounds that can impart off-flavors to the final product; hence, it is essential to separate these compounds from the \"heart cut\", which represents the fraction rich in aroma compounds relevant for the organoleptic quality of the spirit [43]. A fortification grape spirit should exhibit a balance of volatile components, to meet the requirement of not presenting any aroma extraneous to the raw material or defective [44]. The grape spirit may be used for the fortification or may be aged in wood barrels and marketed as aged brandy (Figure 3). Fortification grape spirit is added to fermenting must after 2 to 3 days from the start of the fermentation process, when the sugar content is at least 17.5 g/L. Non-highly rectified grape spirit is added to achieve a final alcoholic content of around 19% (\(v/v\)), representing a distinctive and crucial step [4; 5]. The grape spirit is added at a ratio of one part of grape spirit to four parts of fermenting must. Grape spirits' addition results in fermentation stoppage by induction of toxicity in yeasts due to high alcohol content (ca. 77% \(v/v\) ethanol). This step also promotes anthocyanin and tannin solubilization and the precipitation of insoluble matter [5; 19]. The addition of grape spirits is especially relevant for young Port wine aroma and flavor, as it induces a warm feeling in the mouth and reduces the intensity of tannins and astringency [5]. Port wines can be categorized according to their sweetness and color. According to the sugar content, Port wines are classified as extra dry, dry, semi-dry, sweet, or very sweet. A specific sweetness level is ensured by careful selection of the timing of the fortification. According to the color, Port wines are classified as red (varying from deep purple to light gold), white (pale yellow to golden white), or _rose_ (pink related color) [4]. There are several styles of Port wines defined by the maturation method. It is worth noting that the selection of the fortification spirit is potentially relevant to each style, since the chemical composition of the distilled beverage will have an impact on several organoleptic characteristics of the final product, namely the color, taste, and aroma profile [3; 29]. Ruby style is characterized by a deep red color, full body, fruity aromas, and rich tannins in the mouth. Ruby wines are commonly aged in large old wooden barrels called _Balseiro_ (Figure 3), with the purpose of minimizing the contact between wine and oxygen, for a maximum of three years. This style of Port, in ascending order of quality, includes _Reserva_, Late Bottled Vintage (LBV), and Vintage. Vintage Port is produced from the grapes from a single harvest year, matured in wood for up to three years, and then submitted to a significant period, often many decades, of ageing in bottle. This style of Port wine presents a considerably different character compared to the wines matured uniquely in wood, and they are sold with the harvest date on the label [19]. Tawny Ports usually result from the blending of different batches of wine, aged in smaller vats or wood casks over different periods.