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The beer at this point contains 1000ppm lactic acid, 1000ppm 2,3-butanediol, 250ppm succinic acid, 200ppm acetic acid and 100ppm formic acid. Flacours identified as sweet, honey, fruity, vegetbale or faecal are associated with compounds produced by the Enterobacteriaceae. The slow emegence of the the predominant Saccharomyces species, S. cerevisiae and possibly S. globus is a result of the depletion of wort amino acids by Enterobacteriaceae activity. This signifies the primary period of alcohol production, during which 80% of the wort sugars (glucose, fructose, sucrose, maltose, and maltotriose) are metabolised via the EMP pathway. Ethanol and CO2 are the primary end products. Pre-formed volatile compounds (esters and DMS) may be driven out of the beer by CO2 evolution during this phase.

Higher, or Fusel alcholol synthesis is a feature of Saccharomyces fermentation, occurring during ethanol production. The fusel alchohols impart a plastic or solvent like flavour to the beer. Elevated levels of propanol, amyl alchohol, isobutanol, isoamyl alcohol and phenylethyl alchohol are not noted in lambic beer and are ths not distinctive flavour/aroma components of the style.

A significant proportion of the lambic esters, particularly ethyl acetate and ethyl lactate are produced during this period. Ester impart a full-bodied, floral/fruit flavour/aroma to beers. Excessive levels (noted in lambic beers) may lead to off or overly fruity flavours. Ethyl acetate is formed by a cellular esterification pathway within the yeast cell by a reaction between acetyl-CoA compounds and alcohol, catalysed by the acyl-alcohol transferase enzyme. The resulting ester produces a fruity/solventy taste in the beer and has a threshold detection level of 33pm. The increased ester formation is promoted under the following conditions: Wort density about 13o P, increasing attenuation levels, increasing fermentation temperatures, increasing agitation during fermentation and reducing wort aeration levels. The inverse of these conditions reduce ester formation. A profile of beer components at this stage indicates wort gravity decreased to approx 1.012, alchohol content is 4.5 - 5% v/v, butanediol content is unchanged whilst DMS levels are reduced.

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Continuing our article on Lambic Beers …

The primary phase of lambic fermentation occurs after the “infected” wort is transferred into the fermentation casks. Typical initial temperatures are between 18-20oC, with initial specific gravities ranging from 1.048 - 1.072, depending upon lambic style produced. Initial fermentation during this period is due to the activity of bacteria from the Enterbobacteriaceae family and Kloeckera yeast strains. The cooling wort is readily colonised by the Enterbobacteriaceae, with strains of Enterobacter cloacae and E. aerogene being indicated as the predominant species. Strains of Klebsiella aerogene, Escherichia coli, Citrobacter freundii and Hafnia alevi are also active at this point. All species are capable of fermenting glucose and/or lactose via the Embden-Meyerhof-Parnas (EMP) pathway, but cannot utilise maltose or maltotriose.

The Enterobacter, Keibsiella and Hafnia species utilise a butanediol fermentation, producing 2,3-butanediol, acetoin and ethanol from the metabolism of glucose. E. coli and C. freundii employ a mixed acid fermentation to primarily produce lactic acid and lesser amounts of acetic, succininc and formic acids, ethanol and CO2. The activity of the latter species results in the formation of the majority of acetic acid found in lambic beer. This bacterial activity also results in the production of large amounts (500ppb) of DMS.

The activity of Kloeckera apiculata, a yeast capable of mixed acid fermentation from the metabolism of glucose, during this phase has little impact upon the lambic flavour, as any volatile esters it may produce are lost due to subsequent CO2 evolution. The combination of bacteria and yeast growth within this period has minimal impact upon the worts fermentable sugars, a maximum attenuation of 15% may be realised, however a significant drop in wort pH is apparent, from 5.1 to 4.6 as a resul primarily of acid formation. K. apiculata is gradually supplanted after two weeks by the apperance of the Saccharomyces species, whilst the Enterobacteriaceae disappear after 30-40 days, due to their sensitivy to ethanol concentration above 2% and pH leveles below 5.5 .

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An Introduction to Lambic Beers

The Belgian lambics are unique beers, traditionally produced in the Payottenland region of Belgium, via a process of spontaneous fermentation, as opposed to the controlled inoculation and fermentation procedures used in the production of other beer styles. This type of traditional, spontaneous fermentation is employed in combination with differing raw materials and production processes, to produce beers with unique flavour and aroma profiles, which have not been reproducible via other methods. Spontaneous fermentation is facilitated by overnight exposure of the cooling (un-inoculated) wort to the predominant air borne microflora of the brewery, which rapidly establish themselves within the wort.

There are two major phases of fermentation underaken in lambic beer, both involving the activities of bacteria and yeast; a primary phase, lasting for 3-4 months, characterized by the production of high amounts of ethanol; and a second, slower period of “lambification” or acidification, lasting for 12-24 months. A subsequent third (bottle) fermentation phase may be used to produce a gueuze style lambic.

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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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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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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.

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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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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Extraction and pre-treatments.

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.

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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Douro Environmental Characteristics

Vines are grown on terraces on steep slopes below 450m, in schistose soil containing high levels of granite. Climatic conditions encompass both extremes; hot summers with temperatures above 37°C and freezing winters. Rainfall varies from 400mm – 1000mm.

Grape Varieties

Current European Union (EU) regulation permits 15 red and 14 white varieties for port cultivation. Touriga Nacional is considered to the most important red variety, as it contains high sugar levels and produces highly colored, tannic wines with fruity aromas. Other varieties include Tinta Roriz, Touriga Francisca and Bastardo.

White cultivars include Codega, Rabigato and Malvasia. White and Red varieties are often grown on the same vineyard, and are combined at harvest for crushing.

Harvesting

Harvest procedures are similar to those for Sherry grapes. Harvesting occurs from August through to October, and is performed totally by hand, as a consequence of the steep terrain and terraces vines grow upon. Grapes are picked when analysis confirms high levels of dissolved solids (sugars), which are required by law to yield musts with at least 11% potential alcohol, although much higher levels (12 – 14%) are common. The attainment of such sugar levels is also desirable for the optimum production of pigments, polyphenols and fruit flavors. Harvested grapes are placed in small steel bins for transportation to the winery for immediate pressing. Port grapes are not dried in the sun prior to crushing, as this practice is considered to have a negative impact upon wine quality.

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Definition and Background

The term port is a strictly controlled title (similar to that of Sherry) applied to fortified wines that have been produced in the Douro valley (which encompasses the town of Oporto) in northern Portugal, and matured in this region or in the city of Vila Nova De Gaia. Vineyards in this region are categorized by the local controlling authority, the Casa do Douro, from A to F, with higher grading corresponding to higher proportions of grapes permitted for use in port production.

Unlike Sherry, Port owes much of its flavor to the procedure of fortification in mid fermentation, which serves to retain the varietal characteristics of the producing grape. There are two general styles of Red Port: the soft and sweet Portuguese styles and the tannic, dryer English styles. Alcohol by volume varies from 19 – 22% for these types. White ports are also produced, which may have alcohol volumes as low as 16.5%.

History and Importance

The origins of Port are similar to the origin of Sherry and seem to stretch back to the 17th century, when increasing demand for Portuguese wine in England lead to the export of Douro Valley wine. This style of wine was thin, dry, acidic, with a coarse flavor (due high tannin content) and traveled poorly, thus brandy was added to fortify the wine, preserving it over often length sea voyages around Europe, thus producing the port wines of today, although production practices have changed slightly.

Although demand for Port is declining, the production of this wine is extremely significant to the Portuguese national economy.

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