The Beer Brewer

This continues the previous articcle on “Maturation and Individual Wine Characteristics”

Other products, such as terpenes and lactones are also formed at this stage by the yeast, which also contribute to the fino character. Terpenes are synthesized by the flor yeasts, and produce rose like, or floral aromas in the wine. Lactones are esters synthesized by yeast and appear to originate from an esterification reaction between α –ketobutyric acid and acetaldehyde. They are responsible for strong nutty aromas. Some of the lactone precursors may be extracted from the wooden cask material by the ethanol within the wine.
Although great care is taken not to disturb flor films, regular removal every three months and replenishment of wine (from the same anada or vintage) is required to replenish diminishing oxygen levels and nutrients, which are crucial to maintaining a flor coverage.

Wines with flor remain unblended for a year, after which time they become part of the unique solera system (Figure 3) common to all Sherries. This system is a form of blending, facilitated by topping up of older butts with young wine from more recent vintages, to achieve age and consistency in the final product. This system is composed of a number of stages or criadera, (which vary from producer to producer), each containing wine at a particular age, with the oldest stage being that of the solera stage or solera. As wine is removed from the solera for bottling, the partially empty butts are refilled with wine from the first (or next oldest) criadera or stage. The first criadera is thus replenished from the second (or next oldest) criadera and so on throughout the numerous criaderas, with the final, youngest criadera refilled with a suitable wine from the same vintage (anada). Wines drawn from individual butts in a criadera are blended together before being added to the next criadera, thus ensuring product consistency during production. This indicates solera systems for fino wines may involve up to 600 butts, arranged in one solera and five criaderas. Aging of fino types takes at least three years and may extend to eight.

Finos emerge with 15.5 – 17% alcohol by volume, a distinct pungent (green) aroma and a dryness that lacks acidity.

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Wine maturation occurs in American oak butts of 500 – 600 l capacity, which are stacked in tall, well ventilated buildings (Bodegas) which maintain a cool environment. Internal humidity is maintained above 60% by frequent watering, preventing excessive evaporation of water (through the wooden maturation vessels) from the wine.
Butts containing fino type wines are filled to 80% capacity, to maintain sufficient air/liquid interface to allow the spontaneous formation of the flor yeasts, so crucial in producing quality fino Sherry with the required characteristics. Temperatures must be maintained between 15 - 20°C to ensure flor initiation will occur. The flor is a film of yeast, created by the activity of S. cerevisiae type yeasts (S. beticus, S. cheresiensis), that float on the surface of the wine, preventing the exposure of wine to oxygen, (which may cause browning due to the oxidation of phenols) and film forming, acetic acid producing spoilage organisms. Flor yeasts possess an aerobic metabolism which leads to the metabolism of compounds within the wine: ethanol is consumed as a carbon source (1 – 1.5% v/v) and is replenished accordingly (via refortification), acetic and lactic acids are reduced (to acetaldehyde and esters), from 0.4 g l-1 to 0.04 g l-1, and glycerol is reduced from 8g l-1 to 0.5 g l-1. The large amounts of acetaldehyde (responsible for the pungent “green” aroma of the wine) that are common in such wines, 260 – 360 mg l-1, are the result of oxidative alcohol dehydrogenation by the flor yeasts. Acetaldehyde derivatives (which contribute to fino character), such as 1,1 diethoxyethane and acetoin also increase during flor maturation, to 40 – 75mg and 8 – 19 mg l-1 respectively. 1,1 diethoxyethane is an acetal compound formed via a chemical pathway from acetaldehyde and is partly responsible for the fruity aroma of the wine. A proposed pathway for the formation of acetoin by yeast involves a reaction between active acetaldehyde (acetaldehyde-TPP complex, formed from the decarboxylation of pyruvate) and acetyl coA, via the action of diacetyl synthetase enzyme, to produce diacetyl. The enzyme diacetyl reductase then reduces diacetyl to acetoin.

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This is part 1 of an ongoing publication on fortified wines and sherry.

author: The Master Brewer English-Australian copyright 2007

Definition of a Fortified Wine

Before proceeding to describe sherry and port wine production, if may be of benefit to define the category that these wines fall into: Both are classified as fortified wines (containing between 15 – 22% alcohol by volume), on account of both styles receiving fortification with a wine derived spirit at some point in the production process, rather than achieving final alcohol volumes by fermentation only.

Definition of Sherry and Sherry Style Wines

The term Sherry describes a range of fortified, white dessert wines, produced in the southern region of Spain (Andalusia), around the area of Jerez de la Frontera, in the province of Cadiz. This style of wine is a geographical appellation (European regulation), therefore only the wines produced in this designated area may bear the name Sherry . There are three main types of Spanish Sherry, fino, amontillados and oloroso, which are described hereafter.
Further European regulation stipulates dry and medium style sherries are required to contain a minimum of 15% alcohol, and cream sherries 15.5% . Outside Europe, wine styles similar to Sherry, that may or may not utilize similar production techniques to that used in Jerez, are often termed Sherry style, or carry the producing countries name appended to the term sherry.
The traditional method of sherry production utilized in Jerez (the solera method) is initially considered hereafter. Other methods will be briefly compared subsequently.

Check back for part 2 shortly ….

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