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This is the concluding part of the Maturation and Wine Characteristics. The work continues though!

A loss of the flor may occur in fino types not regularly replenished or of considerable age, which results in the production of richer amontillado type wines. Wines designated for this style are re-fortified to 17.5% alcohol by volume and aged in subsequent solera systems in the bodega for at least eight years, in butts filed to 95% capacity . Oxidation of the wine in the soleras occurs, transforming the pale wine into a dark gold color. Characteristic nutty flavors are also evident in the product, which are created by a combination of compound oxidation, esterification and concentration of fusel oils and other non volatile compounds due to the process of evaporation in the wooden butts. This wine displays a fino aroma, but a fuller body.

As previously mentioned, oloroso wines do not develop flor yeast, thus such types undergo a process of aging similar to amontillado types. Butts are filled to 95% of capacity and stored in warmer parts of the bodega, as temperature control is not needed to ensure flor formation. This warmth may aid extraction of phenolic compounds from the oak, which contribute to the oxidation of the wine. Oloroso solera systems contain less ciradera stages and blending is more limited, thus slightly more barrel to barrel variation may occur in these wines. Maturation is similar to the oxidative process described for the amontillado types above, with color and flavor forming via the oxidation of phenolic compounds in the wine and a concentration effect. Esters and volatile acid levels in the wine increase, due to the conversion of acetaldehyde to acetic acid, which may combine with ethanol to produce ethyl acetate. Wines emerge fairly dry, although sweetness and body is more evident in this style than in fino Sherry, as glycerol formed in initial fermentation is not utilized by the flor yeasts and is therefore present in concentrations between 7 – 9 g l. Oloroso wines contain 17- 18% alcohol by volume.

Raya style Sherry is a form of oloroso that is matured in direct sunlight, due to high phenol content of the wine. A very dark wine is formed from the oxidative reactions that subsequently occur. Raya are typically blended with oloroso wines before sale.

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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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