Port Style Wines

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This post conlcudes our article on Port & Sherry and we’ll be moving on to Lambic Beers shortly … stay tuned at The Beer Brewer!

Australia produces port style wines, although the term port may not be applied to wines destined for the international market.

The grape varieties and production methods utilized significantly differ from those described above, although one producer (Hardys) uses Portuguese methods as outlined above. Shiraz or Grenache grapes are used, with baking or thermovinification processes used to produce the wine.

Baking techniques are very similar to those described in the Sherry section of this paper, and produce a similar wine, displaying caramelized (oxidized) characteristics.

Thermovinification involves exposing grape varieties to heat sources, typically steam or boiling water, to extract pigments. Fortification may occur after fermenting the wine dry (as occurs with Sherry); sweetness is added with concentrates. As the processes for the production of port and Sherry style wines are similar, there may be little difference between the two types of wine. Minor differences may be attributable to the characteristics of the grape variety utilized.

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Port Wine Characteristics

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Unlike Sherry, grape variety is central to the flavor of port; however type and length of maturation determine the ports final characteristics, as with Sherry styles.
Total titratable acidity of port ranges from 3.45 – 5.86 g l, as tartaric acid, volatile acidity (as acetic acid) is less than 0.35 g l.

Ruby ports are usually darker in color (dark red) than tawnies, due to less time spent in the cask during maturation. Levels of phenolic material are higher in such styles, which impart slightly astringent flavors. Fruity aromas are very evident.

Tawny ports are lighter in color, typically amber in hue, displaying complex dried fruit flavors that are less astringent than rubies, often with ‘oaked’ characteristics in evidence. This is due to the extended contact of the wine with the wood, reducing levels of phenols and extracting compounds from the wood. Aromas are often more spicy.

Vintage ports are more complex again, in part due to production from a single selected vintage and minimal wood aging. The content of the must has a very significant influence on final flavor. Such styles exhibit complex, fruity aroma and flavor characteristics, with a full bodied mouth feel and purple-red coloration.

Little information exists on the subject of white port, although such types appear to be lighter, both in color and flavor, due to minimal contact with skins during extraction and wood during maturation. White styles are often dry (English style), but may be blended with sweeter white wines, to produce Portuguese style wine.

As is the case with Sherry wines, alcohol by volume increases with increased color of the wine.

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Port Blending, Spoilage, Stabilization and Blending

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Blending of Port

Blending procedures are significantly different from those used for Sherry. Blending may occur during maturation or pre shipping/bottling, with wines from the same vintage or untreated (matured) wines at various ages. The type of wine blended and amounts utilized are dependent upon the required attribute for each style, and thus vary between producers/blenders. Sweetening/coloring wines, which are fortified to 20% alcohol, may be added to ruby/tawny ports, if producing the Portuguese style of port, as opposed to the English style. Vintage ports are blends of the same vintage, which are mixed prior to bottling.
wine bottles

Spoilage

Primarily due to the metabolism of wine sugars by heterofermentative Lactobacillus species that display ethanol tolerance.

Stabilization and Bottling

Stabilization procedures are similar to those used for Sherry wine. Ruby and tawny ports are clarified with fining agents (to remove color and tannins) before being stabilized for one week at cold temperatures, usually – 8°C . Filtration subsequently occurs, using diatomaceous earth, before membrane filtration (1.2 – 3.0µ) proceeds prior to bottling.
Little information relates to the white port styles, although similar procedures to those used for the stabilization and clarification of Sherry would conceivably be used.
Vintage ports destined for bottle maturation are not cold stabilized or filtered, as the sediment is considered essential to the aging of the wine.

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Port Maturation

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These young port wines have high levels of grape derived phenolic material, particularly tannins, which produce astringent flavors if not mellowed by wood or bottle maturation for a period of at least three years.

The young port is stored in wooden vats over the winter in the Douro area. During this time color is increased due to anthocyanin- aldehyde- tannin reactions. Between November and March the wine is refortified to 21%, racked into casks and classified.

Red port is designated into three types, ruby, tawny and vintage, prior to maturation. This designation determines the type and length of maturation.
- Ruby port experiences maturation for 3 – 5 years in the wood
- Tawny ports mature for 30 years and beyond
- Vintage styles have 2 – 3 year wood maturation before bottle aging, often for lengthy periods (up to 50 years)

Red port is usually shipped to the city of Vila Nova De Gaia, which has a more stable climate (thus avoiding baked characters, due to heating) more suited to the maturation of the port.

The casks or pipes used in ruby and tawny port maturation are only partially filled, to enable oxidative reactions to occur in a process akin to that used for oloroso Sherry. Racking of wine into re-sanitized casks occurs every three months, to maintain oxygenation of the wine, although fractional blending of the wine does not occur i.e. no solera system. Blending uses wine from the same vintage, and may be added to the racked wine, as may also the brandy spirit. The procedure of racking also serves to lighten the color of the port, as insoluble tannin complexes form (due to oxidation) that include anthocyanins, that are left in the cask upon racking.

During oxidative aging increasing amounts of esters are formed (as previously described in Sherry) to produce ethyl esters of lactic, malic, succininc and tartaric acids (the types of acids are influenced by grape variety). These esters contribute minimally to the aroma of the wine, although they have a significant impact upon the wine character, enhancing mouth feel and producing fuller tastes.

Polymerization of aldehydes also occurs during maturation upon wood, which leads to the nutty/woody flavors encountered in such styles.

Conversely, designated vintage ports are not matured under oxidizing conditions, although they spend two years maturing upon the wood, before aging in the bottle for up to 50 years. Racking during wood maturation is infrequent, thus color loss is not as extensive in these styles. Vintage ports will develop some flavors during wood maturation, although individual characteristics occur during bottle aging.

White port usually matures better under the harsher climate of the Douro, and is often matured for up to three years in concrete pipes, which prevent color increase that may occur in wood.

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Port Production

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Extraction and pre-treatments.

Vineyard
Grape crushing is also similar to that used by Sherry manufacturers, i.e. grapes are conveyed via a screw to the crusher, although destemming does occur, to prevent unwanted bitter flavors occurring in the wine. Separation of must with differing polphenol contents does not occur post crushing (as with Sherry), as pressing (juice extraction from skins) does not occur at this stage. The juice is pumped into open fermentation tanks for initial fermentation. The Must has a low total acidity (6 g l, as tartaric acid) and a pH of approximately 4, although correction to pH 3.6 occurs, as does the addition of sodium metabisulphate (100mg/l) to reduce microbial load and aid the extraction of grape pigments.

Base Wine Fermentation

As is the case with Sherry manufacture, inoculation with specific yeast strains may occur in the fermentation vessel, otherwise spontaneous fermentations occur from strains in the winery/grape micro flora, which are Sachharomyces cerevisiae type yeasts. Alcoholic fermentation and the products of (acetaldehyde, esters, etc) are the same as that described for Sherry production. Glycerol is formed during alcoholic fermentation, levels reaching 3 – 8 g l. Other important port flavor compounds produced during this period (by the yeast) are butanol, isobutanol, hexanal

(a volatile aldehyde produced from the oxidation of unsaturated fatty acids and acetate.

Red Port Vinification: This process is significantly different than the process utilized for Sherry production, as a red base wine is produced (rather than white) which is fortified mid fermentation.

Barrels

Fermentation of this port style occurs at temperatures slightly higher than that of Sherry ~ 28°C, primarily to influence the microbial population in the must, produce fruity flavors and ensure efficient extraction of required pigments. Fermentation progresses for a duration of 2 – 3 days, during which time maximum extraction of phenolic compounds and anthocyanin pigments must occur. Therefore, there must be maximum contact between the juice and the grape skins, which is facilitated by various autovinifiers, which spray juice onto the crust of skins that forms over the juice during fermentation, due to the action of evolved CO2.

Fermentation over this period results in a decrease in must specific gravity, from 1.090 – 1.100 to 1.045 – 1.050. Fermentation does not go to completion as with Sherry production, as at this point the fermenting must is run off the solid material and into a suitable vessel (wood or steel), where fortification occurs with a brandy spirit of 75% volume, to increase alcohol by volume to 19 – 20%, thus terminating the fermentation and creating port. The brandy contributes 20% of the total wine volume and is non-neutral in character, making a significant contribution to the character of the wine, adding esters, higher alcohols and acetaldehydes states that fortification at this point serves to retain large amounts of acetaldehyde (a product of yeast fermentation) in the wine, stabilize color by forming anthocyanin – tannin polymers and to mask (typical levels of 500mg/l-1 bitterness by retaining sweetness.

The must solids are often pressed and juices with various levels of tannins are produced (similar to those described in Sherry), some of which are blended with the port, and that with high tannin used to produce spirit. Port pH is corrected to 3.6 with tartaric acid, to correct the rise in must pH due to the addition of the spirit.
White Port Vinification: Juices for white styles may contain grape skins up to the point of fermentation initiation, before racking off the solids occurs and fermentation continues. This produces a harder style wine with increased browning potential, due to the extraction of phenolic compounds. Fermentation temperatures are often lower than that of red port, around 18 – 20°C, to retain required fruity aromas that may be driven off at higher fermentation temperatures. White ports are combined with juice from the pressed solid materials, to achieve tannin levels desired by the manufacturer, however fashionable, lighter style ports may not include such juice to preserve delicate flavours.

Typically, both red and white ports experience fermentation to consume half of the fermentable sugars, leaving between 80 – 120 g sugars per liter, however sweeter styles are produced (geropigas), with residual sugars up to 150 g/l. Dry styles are also produced for blending purposes, which contain sugars up to 50 g/l.

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