Port wine

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This article is about the type of wine. For the birthmark, see Port-wine stain. For the Krazy Kat short, see Port Whines.
A 10-year aged tawny port
Official guarantee label from a bottle of Port

Port wine (also known as Vinho do Porto, Portuguese pronunciation: [ˌviɲuduˈpoɾtu], Porto, and usually simply port) is a Portuguese fortified wine produced exclusively in the Douro Valley in the northern provinces of Portugal.[1] It is typically a sweet, red wine, often served as a dessert wine though it also comes in dry, semi-dry, and white varieties. Fortified wines in the style of port are also produced outside Portugal, most notably in Australia, South Africa, Canada, India, Argentina, and the United States. Under European Union Protected Designation of Origin guidelines, only the product from Portugal may be labelled as port or Porto.[2] In the United States, wines labelled "port" may come from anywhere in the world,[3] while the names "Dão", "Oporto", "Porto", and "Vinho do Porto" have been recognized as foreign, non-generic names for wines originating in Portugal.[4]

Region and production[edit]

The vineyards that produce port wine are common along the hillsides that flank the valley of the River Douro in northern Portugal

Port is produced from grapes grown and processed in the demarcated Douro region.[5] The wine produced is then fortified by the addition of a neutral grape spirit known as aguardente in order to stop the fermentation, leaving residual sugar in the wine, and to boost the alcohol content. The fortification spirit is sometimes referred to as brandy but it bears little resemblance to commercial brandies. The wine is then stored and aged, often in barrels stored in a cave (pronounced kahv and meaning "cellar" in Portuguese) as is the case in Vila Nova de Gaia, before being bottled. The wine received its name, "port", in the later half of the 17th century from the seaport city of Porto at the mouth of the Douro River, where much of the product was brought to market or for export to other countries in Europe. The Douro valley where port wine is produced was defined and established as a protected region, or appellation in 1756, making it the oldest defined and protected wine region in the world. Chianti (1716) and Tokaj (1730) have older demarcation but no regulation associated and thus, in terms of regulated demarcated regions, Porto is the oldest.

The reaches of the valley of the Douro River in northern Portugal have a microclimate that is optimal for cultivation of olives, almonds, and especially grapes important for making port wine. The region around Pinhão and São João da Pesqueira is considered to be the centre of port production, and is known for its picturesque quintas—farms clinging on to almost vertical slopes dropping down to the river.

Wine regions[edit]

The demarcation of the Douro River Valley includes a broad swath of land of pre-Cambrian schist and granite. Beginning around the village of Barqueiros (located about 70 kilometres (43 mi) upstream from Porto), the valley extends eastward nearly to the Spanish border. The region is protected from the influences of the Atlantic Ocean by the Serra do Marão mountains. The area is sub-divided into 3 official zones-the Baixo (lower) Corgo, the Cima (higher) Corgo and the Douro Superior.[6]

  • Baixo Corgo – The westernmost zone located downstream from the river Corgo, centered on the municipality of Peso da Régua. This region is the wettest port production zone, receiving an average of 900 mm, and has the coolest average temperature of the three zones. The grapes grown here are used mainly for the production of inexpensive ruby and tawny ports.[6]
  • Cima Corgo – Located further upstream from the Baixo Corgo, this region is centered on the town of Pinhão (municipality of Alijó). The summertime average temperature of the regions are a few degrees higher and rainfall is about 200 mm less. The grapes grown in this zone are considered of higher quality, being used in bottlings of vintage and Late Bottled Vintage Ports.[6]
  • Douro Superior – The easternmost zone extending nearly to the Spanish border. This is the least cultivated region of Douro, due in part to the difficulties of navigating the river past the rapids of Cachão da Valeira. This is the most arid and warmest region of the Douro. The overall terrain is relatively flat with the potential for mechanization.[6]

Grapes[edit]

Over a hundred varieties of grapes (castas) are sanctioned for port production, although only five (Tinta Barroca, Tinta Cão, Tinta Roriz (Tempranillo), Touriga Francesa, and Touriga Nacional) are widely cultivated and used.[7] Touriga Nacional is widely considered the most desirable port grape but the difficulty in growing it and the small yields cause Touriga Francesa to be the most widely planted grape.[7] White ports are produced the same way as red ports, except that they use white grapes—Donzelinho Branco, Esgana-Cão, Folgasão, Gouveio, Malvasia Fina, Rabigato and Viosinho. While a few shippers have experimented with Ports produced from a single variety of grapes, all Ports commercially available are from a blend of different grapes. Since the Phylloxera crisis, most vines are grown on grafted rootstock, with the notable exception of the Nacional area of Quinta do Noval, which, since being planted in 1925, has produced some of the most expensive vintage ports.

Grapes grown for port are generally characterised by their small, dense fruit which produce concentrated and long-lasting flavours, suitable for long aging. While the grapes used to produce port produced in Portugal are strictly regulated by the Instituto do Vinho do Porto, wines from outside this region which describe themselves as port may be made from other varieties.

Transport[edit]

A barcos rabelos carrying some Port wine barrels.

While port is produced from grapes grown in the Douro valley, until 1986 it could only be exported from Portugal from Vila Nova de Gaia near Porto, Portugal's second-largest city.[5] Traditionally, the wine was taken downriver in flat-bottom boats called 'barcos rabelos',[8] to be processed and stored.[8] However, in the 1950s and 1960s, several hydroelectric power dams were built along the river, ending this traditional conveyance down the river. Currently, the wine is transported from the vineyards by tanker trucks and the barcos rabelos are only used for racing and other displays.

Properties[edit]

Port wine is typically richer, sweeter, heavier, and possesses a higher alcohol content than unfortified wines. This is caused by the addition of distilled grape spirits (aguardente similar to brandy) to fortify the wine and halt fermentation before all the sugar is converted to alcohol and results in a wine that is usually 19 to 23% alcohol.

Port is commonly served after meals as a dessert wine in English-speaking countries, often with cheese; white and tawny ports are often served as an apéritif. In Europe all types of port are frequently drunk as aperitifs.

Styles[edit]

Different port wines with corresponding colour.
Aging in wooden barrels

Port from Portugal comes in several styles, which can be divided into two broad categories:

  • Wines matured in sealed glass bottles, with no exposure to air, experience what is known as "reductive" ageing. This process leads to the wine losing its colour very slowly and produces a wine which is smoother on the palate and less tannic.
  • Wines that have matured in wooden barrels, whose permeability allows a small amount of exposure to oxygen, experience what is known as "oxidative" ageing. They too lose colour, but at a faster pace. They also lose volume to evaporation (angel's share), leaving behind a wine that is slightly more viscous.

The IVDP (Instituto dos Vinhos do Douro e Porto) further divides port into two categories: normal ports (standard rubies, tawnies and white ports) and Categorias Especiais, special categories, which include everything else.

Tawny port[edit]

Tawny ports are wines, made from red grapes, that are aged in wooden barrels, exposing them to gradual oxidation and evaporation. As a result, they gradually mellow to a golden-brown colour. The exposure to oxygen imparts "nutty" flavours to the wine, which is blended to match the house style.

Tawny ports are sweet or medium dry and typically consumed as a dessert wine.[5]

When a port is described as tawny, without an indication of age, it is a basic blend of wood aged port that has spent at least two years in barrels. Above this are tawny with an indication of age which represent a blend of several vintages, with the nominal years "in wood" stated on the label. The official categories are 10, 20, 30 and over 40 years. The categories indicate a target age profile for the ports, not their actual ages, though many people mistakenly believe that the categories indicate the minimum average ages of the blends. It is also possible to produce an aged white port in the manner of a tawny, with a number of shippers now marketing aged white ports.

Colheita[edit]

A vintage Colheita tawny.

A tawny port from a single vintage is called Colheitas. Instead of an indication of age (10, 20...) the actual vintage year is mentioned. However, they should not be confused with vintage port (see below): whereas a vintage port will have been bottled about 18 months after being harvested and will continue to mature, a Colheita may have spent 20 or more years in wooden barrels before being bottled and sold. A number of white Colheitas have also been produced.

Garrafeira[edit]

Garrafeira is an unusual and rare intermediate vintage dated style of port made from the grapes of a single harvest that combines the oxidative maturation of years in wood with further reductive maturation in large glass demijohns. It is required by the IVDP that wines spend some time in wood, usually between three and six years, followed by at least a further eight years in glass, before bottling. In practice the times spent in glass are much longer. The style is most closely associated with the company Niepoort, although others do exist. Their dark green demijohns, affectionately known as bon-bons, hold approximately 11 litres each. Some connoisseurs describe Garrafeira as having a slight taste of bacon, although many people will neither notice nor understand such a description; the reason being that, during the second phase of maturation, certain oils may precipitate, causing a film to form across the surface of the glass that can be tasted by those who are accustomed to the difference between Garrafeira and other forms of port.

Confusingly, the word Garrafeira may also be found on some very old tawny labels, where the contents of the bottle are of exceptional age.

Ruby port[edit]

Rabelos, a type of boat traditionally used to transport barrels of port down the River Douro for storage and aging in caves at Vila Nova de Gaia near Porto

Ruby port is the cheapest and most extensively produced type of port. After fermentation, it is stored in tanks made of concrete or stainless steel to prevent oxidative aging and preserve its rich claret colour. The wine is usually blended to match the style of the brand to which it is to be sold. The wine is fined and cold filtered before bottling and does not generally improve with age.

Reserve or vintage character[edit]

Reserve port is a premium ruby port approved by the IVDP's tasting panel, the Câmara de Provadores. In 2002 the IVDP prohibited the use of the term "Vintage Character", as the wine had neither a single vintage (usually being a blend of several vintages of ruby port) nor the typical character of vintage port.[9]

Rose port[edit]

Rose port is a very recent variation on the market, first released in 2008 by Poças and by Croft,[disambiguation needed] part of the Taylor Fladgate Partnership. It is technically a ruby port, but fermented in a similar manner to a rosé wine, with a limited exposure to the grape skins, thus creating the rose colour. It has enjoyed little critical acclaim.[citation needed]

White port[edit]

White port is made from white grapes and can be made in a wide variety of styles, although until recently few shippers have produced anything other than a standard product. Ordinary white ports make an excellent basis for a cocktail while those of greater age are best served chilled on their own. Sweet white port and tonic water is a commonly consumed drink in the Porto region. There are a range of styles of white port, from dry to very sweet. When white ports are matured in wood for long periods, the colour darkens, eventually reaching a point where it can be hard to discern (from appearance alone) whether the original wine was red or white.

Late bottled vintage (LBV)[edit]

Late bottled vintage (often referred to simply as LBV) was originally wine that had been destined for bottling as vintage port, but because of lack of demand was left in the barrel for longer than had been planned. Over time it has become two distinct styles of wine, both of them bottled between four and six years after the vintage, but one style is fined and filtered before bottling, while the other is not.

The filtered wine has the advantage of being ready to drink without decanting and is usually bottled in a stoppered bottle that can be easily resealed. However many wine experts feel that this convenience comes at a price and believe that the filtration process strips out much of the character of the wine.[10]

The accidental origin of late bottled vintage has led to more than one company claiming its invention. The earliest known reference to a style of port with this name in a merchant's list is to be found in The Wine Society's catalogue from the spring of 1964; which includes Fonseca's Quinta Milieu 1958, bottled in the UK, also in 1964.

Unfiltered wines are mostly bottled with conventional driven corks and need to be decanted. After decanting they should be consumed within a few days. Recent bottlings are identified by the label wording "unfiltered" or "bottle matured" or both. Before the 2002 regulations, this style was often marketed as '"traditional", a description that is no longer permitted.

LBV is intended to provide some of the experience of drinking a vintage port but without the need for lengthy bottle ageing. To a limited extent it succeeds, as the extra years of oxidative ageing in barrel does mature the wine more quickly.

Typically ready to drink when released, LBV ports are the product of a single year's harvest and tend to be lighter bodied than a vintage port. Filtered LBVs can improve with age, but only to a limited degree; whereas the unfiltered wines will usually be improved by extra years in the bottle. Since 2002, bottles that carry the words "bottle matured" must have enjoyed at least three years of bottle maturation before release.

Crusted[edit]

Crusted port is usually a blend of port wine from several vintages, although single vintage crusted ports have sometimes been made in the past. Unlike vintage port, which has to be sourced from grapes from a single vintage, crusted port affords the port blender the opportunity to make best use of the varying characteristics of different vintages.

Crusted port is bottled unfiltered, and sealed with a driven cork. Like vintage port it needs to be decanted before drinking.

Although crusted ports will improve with age, the blender often seeks to make these wines approachable at a younger age than for vintage ports. The date on a crusted port bottle refers to the bottling date, not the year the grapes were grown.

While crusted port is required to be aged in bottle for at least three years before it is released to the market, most producers keep the bottles for considerably longer, so they are ready to be drunk when sold, and may be enjoyed by consumers who have no space to cellar bottles. This makes crusted port a popular and affordable alternative to vintage port.

Vintage port[edit]

Vintage port from 1870 and 1873

Vintage port is made entirely from the grapes of a declared vintage year and accounts for about two percent of overall port production. Not every year is declared a vintage in the Douro. The decision on whether to declare a vintage is made in the spring of the second year following the harvest. The decision to declare a vintage is made by each individual port house, often referred to as a "shipper".

The port industry is one where reputations are hard won and easily lost, so the decision is never taken lightly. During periods of recession and war, potential "declarations" have sometimes been missed for economic reasons. In recent years, some shippers have adopted the "chateau" principle for declarations, declaring all but the worst years. More conventional shippers will declare, on average, about three times a decade.

While it is by far the most renowned type of port, from a volume and revenue standpoint, vintage port actually makes up only a small percentage of the production of most shippers. Vintage ports are aged in barrels for a maximum of two and a half years before bottling, and generally require another ten to forty years of ageing in the bottle before reaching what is considered a proper drinking age. Since they are aged in barrels for only a short time, they retain their dark ruby colour and fresh fruit flavours. Particularly fine vintage ports can continue to gain complexity and drink wonderfully for many decades after they were bottled. It is not uncommon for 19th century bottles to still be in perfect condition for consumption.

Single quinta vintage port[edit]

Single quinta vintage ports are wines that originate from a single estate, unlike the standard bottlings of the port wine houses which can be sourced from a number of quintas. Single quinta bottlings are used in two different ways by different producers. Most of the large port wine houses have a single quinta bottling which is only produced in some years when the regular vintage port of the house is not declared. In those years, wine from their best quinta is still bottled under a vintage designation, rather than being used for simpler port qualities. In a sense, this kind of single quinta is a "second wine" of the regular vintage port and is typically sold slightly cheaper than the regular vintage Port. Graham's Quinta dos Malvedos and Taylor's Quinta de Vargellas are examples of this kind of port. Typically, this type of single quinta bears the name of both a major port wine house and the name of a quinta.

In recent times, there has also been an increase in the production and marketing of single quinta vintage port as high-end wines. Vintage port from small producers situated in the Douro valley are almost always single quinta wines and labelled as such. Some of the larger port wine houses also have introduced single quintas which are run as separate estates, rather than as a source of wine for the house's main bottling. Symington Family Estates' Quinta do Vesuvio is an example of this. Typically, this type of single quinta only bears the name of its quinta.

Much of the complex character of aged vintage port comes from the continued slow decomposition of grape solids in each bottle. However, these solids are undesirable when port is consumed, and thus vintage port typically requires a period of settling before decanting and pouring.

Vintage port should not be confused with "late bottled vintage" (see above).

Vintages[edit]

The term vintage has a distinct meaning in the context of vintage port. While a vintage is simply the year in which a wine is made, most producers of vintage port restrict their production of year-labeled bottlings to only the best years, a few per decade.

If a port house decides that its wine is of quality sufficient for a vintage, samples are sent to the IVDP for approval and the house declares the vintage. In very good years, almost all the port houses will declare their wines.

In intermediate years, the producers of blended vintage ports will not declare their flagship port, but may decide to declare the vintage of a single quinta, e.g., the 1996 Dow's Quinta do Bomfim and Taylor's Quinta de Vargellas. Some houses now choose to declare their wines on all but the worst years: Quinta do Vesuvio has declared a vintage every year with the exceptions of 1993 and 2002.

Improved wine-making technologies and better weather forecasts during the harvest have increased the number of years in which a vintage can be declared. Although there have been years when only one or two wines have been declared, it is over thirty years since there was a year with no declarations at all.

History and tradition[edit]

The wine producing Douro region is the third oldest protected wine region in the world after the Tokaj-Hegyalja region in Hungary, established in 1730, and Chianti, in 1716.

In 1756, during the rule of the Marquês de Pombal, the Companhia Geral da Agricultura das Vinhas do Alto Douro (C.G.A.V.A.D., also known as the General Company of Viticulture of the Upper Douro or Douro Wine Company), was founded to guarantee the quality of the product and fair pricing to the end consumer. The C.G.A.V.A.D. was also in charge of regulating which port wine would be for export or internal consumption and managing the protected geographic indication.[11]

Port became very popular in England after the Methuen Treaty of 1703, when merchants were permitted to import it at a low duty, while war with France deprived English wine drinkers of French wine. Contrary to popular belief, Port was not created by British sailors by spiking the wine with brandy to avoid spoilage during the long voyage north. More accurately, British importers could be credited for recognizing that a smooth, already fortified wine that would appeal to English palates would coincidentally survive the trip to London. In 1678, a Liverpool wine merchant sent two new representatives to Viana do Castelo, north of Oporto, to learn the wine trade. While on a vacation in the Douro, the two gentlemen visited the Abbot of Lamego, who treated them to a "very agreeable, sweetish and extremely smooth" wine," which had been fortified with a distilled spirit. The two Englishmen were so pleased with the product that they purchased the Abbot's entire lot and shipped it home.[12]

The continued English involvement in the port trade can be seen in the names of many port shippers: Cockburn, Croft, Dow, Gould, Graham, Osborne, Offley, Sandeman, Taylor and Warre being amongst the best known. Shippers of Dutch and German origin are also prominent, such as Niepoort and Burmester. The British involvement grew so strong that they formed a trade association that became a gentlemen's club.

In Australia, dessert wines, including port, are referred to as "stickies."[13]

Storing and serving[edit]

See also: Aging of wine

Port, like other wine, should be stored in a cool but not cold, dark location (as light can damage the port), with a steady temperature (such as a cellar), laying the bottle on its side if the bottle has a cork, or standing up if stoppered.[14] With the exception of white port, which can be served chilled, port should be served at between 15 to 20 degrees Celsius (59 to 68 degrees Fahrenheit). Tawny port may also be served slightly cooler.[15]

Once opened, port generally lasts longer than unfortified wine but is still best if consumed within a short period of time.[clarification needed] Those with stoppers can be kept for a couple of months in a dark place, but if it has a cork it must be consumed sooner.[citation needed] Typically, the older the vintage, the quicker it must be consumed.[14][unreliable source?]

Exposure to oxygen (or oxidation) causes wine to deteriorate after opening. Therefore the longer a port spent in barrels (where it is exposed to air), the longer it will last after opening. A tawny port has already incorporated oxidation into its flavor profile so it will last much longer than a vintage port.[16] This suggests that tawny and ruby ports last the longest after opening, followed by LBVs, with vintage ports deteriorating the quickest.

Port wines that are unfiltered (such as vintage ports, crusted ports and some LBVs), form a sediment (or crust) in the bottle and require decanting. This process also allows the port to breathe; however, how long before serving is dependent on the age of the port (particularly in the case of vintage ports, which, once decanted, are recommended to be consumed within 3–4 days).[17]

Because it is a crucial mistake to disturb the sediment before decanting, which if disturbed may take days to resettle and thus render the bottle undrinkable for the intended event, a unique method of opening the bottle to allow decanting without disturbing the sediment has evolved, using wooden-handled heated (red-hot) iron 'port tongs', the business end of which have been bent to, when closed, surround the bottle neck. The technique requires the tong ends to be heated to be glowing fairly red hot and then applied to the bottle neck just below the cork, while the bottle is held firmly in place by the bottom (without any movement which may disturb the sediment). Once the heated tongs have been on the glass for about half a minute, the tongs are sharply twisted, or perhaps more certainly an ice cube or towel dipped in ice water is applied to the hot neck, the effect of which is to cause the bottle neck at the point of heated contact to snap off cleanly (i.e., no shards of glass). Thus, the wine is opened without even the potential for disturbing the sediment inherent in using a corkscrew. Obviously, this requires a practiced hand, and is also quite theatrical and impressive when done correctly (and embarrassing, messy and even dangerous when exhibited by a novice). To ensure no glass or sediment, the port should be poured into the decanter through a filter. Port is the only wine typically opened in this fashion (although any old wine with sufficient sediment could also be, counter-productively struck on the head of the bottle neck to cause it to snap off). The same practice may also be used when opening champagne bottles. While neither holds any practical purpose, the pageantry is enough to rationalize the ritual.

Tradition in the United Kingdom calls for port being served at a formal dinner to be passed to the left ("pass the port to port") and for the bottle or decanter not to touch the table on its way around.[18] Though some cultures reject this tradition.[19]

Instituto dos Vinhos do Douro e do Porto[edit]

The Port and Douro Wines Institute is an official body belonging to the Ministry of Agriculture of Portugal and is a key institution in promoting the industry and knowledge of making port wine. It was previously known as the Instituto do Vinho do Porto.[20]

Port houses[edit]

Producers of port wine are often called "shippers". In the early history of the port wine trade, many of the most powerful shipping families were English; this history can still be seen in the names of many of the most famous port wines such as Graham's, Taylor's, and Dow's. Over the years Portuguese, as well as Dutch, German and Scottish-owned shippers have also become prevalent in the port industry.

A list of some notable shippers and the business groups that own them include:[21]

Port as a primeval remedy for illness[edit]

Port has been used in the past as a healing agent in earlier remedies. The British Prime Minister William Pitt the Younger was given port for gout as a boy. He began at the age of 14 (1773) with a bottle a day according to J. Ehrman (1969): "The Younger Pitt".[22]

A recurring theme in the novels of Anthony Trollope is the partiality of respectable elderly ladies for port which they excuse on the grounds that it is "medicinal".

However, it has been widely documented in the medical literature that alcohol consumption can trigger attacks of gout.

Chemistry of port wine[edit]

Aged Port wine contains a family of blueish phenolic pigments called portosins (vinylpyranoanthocyanins)[23] and oxovitisin A, an oxovitisin, a type of pyranoanthocyanin with a 2-pyrone component.[24]

See also[edit]

References[edit]

  1. ^ Porter, Darwin & Danforth Price (2000) Frommer's Portugal 16th ed. IDG Books Worldwide, Inc. ISBN 0-02-863601-5
  2. ^ Labelling of wine and certain other wine sector products Europa.eu
  3. ^ "Office of the Law Revision Counsel, U.S. House of Representatives"[dead link]
  4. ^ United States Code of Federal Regulations
  5. ^ a b c Porter, Darwin & Danforth Price (2000) Frommer's Portugal 16th ed., p. 402. IDG Books Worldwide, Inc. ISBN 0-02-863601-5
  6. ^ a b c d J. Robinson (ed) "The Oxford Companion to Wine" Third Edition pg 536 Oxford University Press 2006 ISBN 0-19-860990-6
  7. ^ a b Mayson (1999), Port and the Douro, pg 93
  8. ^ a b Porter, Darwin & Danforth Price (2000) Frommer's Portugal 16th ed., p. 305. IDG Books Worldwide, Inc. ISBN 0-02-863601-5
  9. ^ "An explanation of "Vintage Character" from "Britain's oldest wine and spirit merchant"". Bbr.com. Retrieved 2013-10-28. 
  10. ^ Larry Lipson (26 May 2006). "To filter or not to filter? That is the question". L.A. Daily News. Retrieved 28 September 2006. 
  11. ^ J. Robinson (ed) "The Oxford Companion to Wine" Third Edition pg 536–540 Oxford University Press 2006 ISBN 0-19-860990-6
  12. ^ Tom Stevenson "The Sotheby's Wine Encyclopedia" The Fourth Edition pg 334 DK Publishing 2007 ISBN 978-0-7566-3164-2
  13. ^ Michael Dresser (1998-01-04). "Port: The competition is sweet Wine: Producers from all over the world are making fortified dessert wines, and some of them rival the Portuguese originals". The Baltimore Sun. 
  14. ^ a b Portwine.com - Storing (accessed 27December 2007)
  15. ^ Portwine.com - Enjoying (accessed 27 December 2007)
  16. ^ Words About Port (accessed 2 April 2010)
  17. ^ UKwinesOnline - Decanting port Info (accessed 3 July 2008)
  18. ^ Telegraph - Why Pass To The Left? (accessed 27 September 2010)
  19. ^ Vintage Port - Which Way To Pass? (accessed 27 September 2010)
  20. ^ The Port and Douro Wines Institute (accessed 25 September 2010)
  21. ^ Portugal-info.net: Port, accessed on 25 December 2009
  22. ^ J. Ehrman (1969), "The Younger Pitt",
  23. ^ Mateus, N; Oliveira, J; Haettich-Motta, M; De Freitas, V (2004). "New Family of Bluish Pyranoanthocyanins". Journal of biomedicine & biotechnology 2004 (5): 299–305. doi:10.1155/S1110724304404033. PMC 1082895. PMID 15577193. 
  24. ^ Oxovitisins: A New Class of Neutral Pyranone-anthocyanin Derivatives in Red Wines. Jingren He, Joana Oliveira, Artur M. S. Silva, Nuno Mateus and Victor De Freitas, J. Agric. Food Chem., 2010, 58 (15), pages 8814–8819, doi:10.1021/jf101408q

External links[edit]