Fortified Wines

Food, Fermentation and Micro-organisms Charles W. Bamforth Copyright © 2005 by Blackwell Publishing Ltd

Fortified wines are those in which fermented, partially fermented or unfermented grape must is enriched with wine-derived spirit. According to the European Union (EU) regulations, such liquor wines are those with an acquired alcohol content of 15-22% by volume and a total alcohol content of at least 17.5% by volume.

The chief fortified wines are sherry (originating in Spain, notably Jerez de la Frontera, which is in the southern province of Cadiz), port (from Portugal and made from grapes produced in or around the upper valley of the River Douro in the north of the country) and madeira (from the Portuguese archipelago of Madeira).

The wine fortification technology originated in such regions because the local soil and climate were not well suited to the production of wines of inherent excellence. The process also allowed protection against microbial infection during the storage and shipment of products.

Sherry is only made from white grapes, but port and madeira may be produced from either red or white grapes. In no instance is a single product made from a mixture of the two grape types. Wines upon which sherry is based tend to be dry and the fortification occurs post-fermentation. If the sweetness needs to be increased, it is through the addition of grape-derived products downstream. Such additions usually comprise wines that have been fortified at the start of fermentation: by adding alcohol at the start of fermentation, yeast action is arrested (see discussion in Chapter 2 on yeast stress) and accordingly there is retention of sugar.

Port is usually fortified approximately halfway through the primary fermentation, and so tends to be sweeter than sherry through the preservation of unfermented sugars.

Madeira may be fortified through either route depending on the sweetness targeted in the product.

The wines used to make sherry derive much of their character from ageing in oat 'butts'. Sometimes, however, there is the development of flor, a film of yeast on the surface. This yeast may comprise the primary fermenting yeast but may also include other adventitious yeasts from diverse genera.

In contrast, characteristics derived from the grape are substantially more important for wines going into port, especially red port. Much of the character of madeiras develops in the estufagem process, which is a heating of the product at, say, 50°C for 3 months.

Sherry, port and madeira are each blended to the target quality during maturation.

Sherry and madeira are fortified using an essentially neutral spirit containing at least 96% ABV and which is continuously distilled from the wine or from related products (the lees or the pomace). Fortification of port is with wine spirit (76-78% ABV). This spirit does contain substances such as alcohols, esters and carbonyl-containing compounds that contribute directly to the flavour of port.

Sherry

The reader is referred to Reader and Dominguez (2003) for comprehensive details of grapes and vinification techniques; however, these are only subtly different from those employed generally for wines (see Chapter 3).

Nowadays fermentation is likely to be in open cylindrical tanks (500-1000 h L) regulated to ca. 25°C. Rather than employing pure cultures of yeast, starters are prepared using the natural flora on a proportion of grapes harvested before the vintage, the harvest being complete towards the end of September. The initial population will include Hanseniaspora but S. cerevisiae soon predominates. Fermentation is completed to dryness by November and a malolactic fermentation will have been effected by endogenous lactic acid bacteria.

Post-fermentation, the young wines are racked from the lees and fortified with spirit (>95% ABV) produced by the distillation of wine and its by-products (lees, pomace). The spirit is first mixed with an equal volume of wine and settled for some 3 days before using to fortify the main wine. This procedure leads to less generation of turbidity than does addition of undiluted spirit.

The young unaged wines are classified into either finos or olorosos depending on their characteristics. Finos are dry, light and pale gold in colour and have an alcohol content of 15.5-16.5%. They are matured under flor yeast, which tends to develop when the grapes are exposed to cool westerlies when grown on soils rich in calcium carbonate. Olorosos, which are matured in the absence of flor yeast, are dry, rich dark mahogany wines with full noses and alcoholic contents of 21%. The higher levels of polyphenolics in these wines suppress flor development.

Newly fermented wines are left to mature unblended for approximately 1 year. They then pass to a blending process (the 'solera' system), in which the aim is to introduce product consistency. It comprises a progressive topping up of older butts of wine with younger wines (much in the way that balsamic vinegar is derived - see Chapter 9).

A sherry must be aged for a minimum of 3 years before sale. During ageing, flor prevents air from accessing the sherry, and so microbial spoilage and oxidative browning is prevented. If there is no flor, as in olorosos, then oxidative browning can occur. Amontillado sherries are produced with an initial flor maturation followed by ageing in the absence of flor, so oxidation and esterification reactions are prevalent in that style of sherry. The flor process leads to a decrease in volatile acidity and glycerol, as well as an increase in the level of acetaldehyde, the latter meaning that fino sherries have a distinct apple note. Other flavour compounds associated with sherries include 4,5-dimethyl-3-hydroxy-2-(5H)-furanone, which affords a nutty character to sherry matured under flor and ira«j-3-methyl-4-hydroxyoctanoic acid lactone, which emerges from the oak and offers the woody note found in many sherries.

Fino sherries are not usually sweetened, are matured for 3-8 years and have alcohol contents of 15.5-17% ABV. Olorosos and Amontillados are generally sweetened and reach 17-17.5% ABV.

Sherries may be fined, traditionally with egg white although increasingly with isinglass or gelatin. They may be centrifuged before filtering and may also be stabilised by treatment with bentonite.

Finally they are cooled through a heat exchanger and ultra-cooler to reach a temperature between -8°C and —9°C, holding there for 10-14 days to chill out colloidally unstable material. Finely ground potassium bitartrate may be added to promote the nucleation of this material. Finally, the sherry is membrane-filtered to eliminate microbes and some solids, prior to bottling.

Port

The reader is again referred to Reader and Dominguez (2003) for more details on vineyard processes.

Much of the port produced these days is fermented in closed tanks at ca. 16°C with facility for turning the contents. Must is run-off after 2-3 days of fermentation at which point most of the sugars have been converted into alcohol. Fermentation is inhibited by the addition of grape brandy with wine becoming port officially at 19-20% ABV.

Red wines destined for ruby will have been aged for 3-5 years in wood. Those going to tawny will have been aged in wood for more than 30 years. Vintage ports are from wines of a single harvest that are judged to be of outstanding quality. They will be aged in wood for 2-3 years and then the ageing completed in bottle for at least 10 years.

A major contributor to the ageing changes in ruby and tawny is the polymerisation of anthocyanins. This is not only partly through oxidative cross-linking, but also through that induced by acetaldehyde. Other significant aldehydes include the furfurals and lignin degradation products from wood, such as vanillin, syringaldehyde, cinnamaldehyde and coniferaldehyde (Fig. 4.1). Phenols such as guaiacol, eugenol and 4-vinylphenol are also extracted from wood during maturation. Other changes include increases in the level of glycerol and decreases in the levels of citric acid and tartaric acid,

Vanillin

Fig. 4.1 Wood-derived species in port.

Vanillin

Syringaldehyde

Cinnamaldehyde

OCH3

Coniferaldehyde

Fig. 4.1 Wood-derived species in port.

the latter by the deposition of potassium hydrogen tartrate. In the acidic, high ethanol wines, esters are produced by the reaction of ethanol with acetic, lactic, malic, succinic and tartaric acids.

Ports are blended, especially the ruby's. They are clarified with gelatin, casein or egg white. White ports will be treated with bentonite, and centrifu-gation is sometimes employed. Rubies and younger tawnies are cold stabilised by holding at -8°C for 1 week. Alternatively, the chilled wine is passed continuously through a crystallising tank containing a concentrated suspension of crystals of potassium bitartrate. Then the wine is filtered with diatomaceous earth followed by sheet-, cartridge- or membrane filtration.

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Responses

  • samantha forbes
    What does "fined traditionally with egg white" with wine?
    7 years ago

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