# Volatile Composition of Fortification Grape Spirit and Port Wine: Where Do We Stand?
## 3 Port Wine's Production: The Relevance of the Fortification Step  
Port wine production has endured for centuries, and its vinicitation process respects the traditional methods but also takes advantages of new advances in viniculture and enology areas, such as the continuous advances in the development of new equipment, technologies, and enological adjuvants, among others. Figure 3 illustrates the main steps involved in Port wine's production, which includes multiple and sequential steps, namely the fortification step with grape spirits (ca. 77% \(v/v\) ethanol). The harvesting of the grapes and the winemaking process itself take place in the DDR, predominantly in regional cooperatives or _quintas_. But the subsequent steps, namely the maturation and bottling, occur mainly in Vila Nova de Gaia, a city located across from Porto, on the south side of the estuary of the Douro River. The Entreposto of Gaia was created in 1926 for wine storage, because, at the time, companies associated with the Port wine trade were obliged to move or build cellars within Gaia for the ageing of their wines. Since 1986, the exportation of wines directly from the DDR has been authorized [7; 39]. All of the stages illustrated in Figure 3, from the collection of the grapes to the aging of the wine, are properly outlined according to the style of wine that is intended to be produced and are also adapted to the conditions of each vineyard, climatic conditions of the year and cellar facilities. Each producer imprints his own style, respecting Port wine regulations (Regulation No. 84/2010 of 8 February 2010) [40] and considering market trends and the current lifestyle. For instance, the selection of the grape varieties may be performed, according to their anthocyanin and tannins content, and it is essential to ensure the adequate preservation of red wine color and mouthfeel throughout the maturation step, which can take many years or even decades. Indeed, producers' decision-making is increasingly based on objective information; for example, the harvesting process takes place when the grapes present a specific gravity between 1.090 and 1.100, a total acidity between 3.9 and 6.0 g/L (expressed as tartaric acid), a pH around 3.3 to 3.7 (in warmer regions the pH can be as high as 4.0) and phenolic compound concentrations between 0.4 and 0.6 g-L [41]. It is not at all the purpose of this section to detail the various stages involved in the production of Port wine, for which proper regulations and publications already exist [5; 7; 19; 41; 42]; however, production of grape spirits and the fortification stage will be emphasized. The fortification spirits used to produce wine likely to obtain the denomination of origin Porto and Moscatel do Douro must be previously certified by the IVDP, according to Regulation No. 84/2010 of 8 February 2010 [40]. The certification procedure depends on the fulfillment of requirements related to organoleptic properties such as clarity (limpid), color (colorless), aroma and taste (absence of any aroma extraneous to the raw material or defective), and physicochemical characteristics, which include clarity, color, alcoholic grade, total acidity, density, volatile compound content (for instance, ethyl carbamate, total higher alcohols, and acetaldehyde) and mineral content (namely calcium, copper, and iron) [40]. Distillation is the main technological process used to produce grape spirit and consists of the separation of ethanol and other flavor compounds from the water and their transfer to the distillate. There are two main types of distillation equipment. The more traditional method is batch distillation, with a pot still, which originates heavily flavored distillates. Basically, it consists in a copper vessel with a steam tube on top, where the alcohol vapor accumulates. This tube leads to a water-cooled condenser, which allows ethanol to condense. This type of distillation equipment is often used to produce fruit distillates, brandies, and whiskies.