What Is Port Wine Made From?
Port is produced by combining wine and brandy yet its production process is intriguingly complex.
The wine can be produced from as many 82 different grape varieties as permitted by the Instituto do Vinho do Porto. However, the CEVD (Centre of Wine Studies of Douro) used scientific data to outline 30 that it recommends for making quality port.
Out of these, the six most common black grape varieties consist of the following:
- Tinta Amarela
- Tinta Barroca
- Touriga Franca
- Tinta Cão
- Touriga Nacional
- Tinta Roriz
Although each grape is different, they tend to have thick skin that can produce rich tannins. Generally, the Touriga Francesa grape is the most popular as it’s quite easy to cultivate. However, the challenging Touriga Nacional is said to produce the best port wine.
Douro Valley Vineyards
As you can probably imagine, white port is made using white grapes, which tend to be among the following:
- Donzelinho Branco
- Malvasia Fina
Meanwhile, the brandy is known locally as “aguardente” and usually has a strength of around 77% ABV. It’s usually an unaged eau-de-vie de vin that’s quite similar to blanche d’armagnac.
However, despite expectations to the contrary, it doesn’t need to come from Portugal. Indeed, it is often imported from South Africa, which has a strong brandy industry thanks to its Dutch heritage.
How Port Wine Is Made
Port wine grapes are handpicked during harvest in mid-September. However, handpicking doesn’t necessarily suggest a superior technique.
Typically, grapes are handpicked when the tractors struggle with the terrain.
Indeed, the Duoro terraces and steep slopes are too narrow for tractors and protected by UNESCO. Nevertheless, winemakers are able to renovate them or build new ones with permission.
Although most wine is fermented from a single grape variety and occasionally blended later, port wine grape varieties are processed together.
Grape Crushing & Lagares
Once picked and destemmed, the grapes are transferred to inert granite tanks called lagares. A lagar is a wide and low tank with an open-top so the grapes can be crushed. Traditionally, crushing was undertaken by foot treading but many producers have adopted mechanisation.
However, foot treading is quite methodical and not quite as chaotic as you’d expect. That being said, music is often played and the event is treated like a party! It consists of several stages call the corte or “cut” and “liberdade” or “liberty”.
During the corte, the foot readers link up shoulder to shoulder in a line and carefully tread in unison across the lagar to break the grapes, which releases the pulp and juice from the grape’s skins.
Afterwards, the liberdade involves freer movement where the treaders individually move around to ensure the skins remain submerged under the surface.
The grapes are left in the lagars for around three days, which allows the juices to macerate with the skins and seeds. Wooden plungers called macacos are used to ensure that the skins stay under the surface. During this time, the juice will develop the desired colour and level of tannins for the port wine.
Port Wine Fermentation
Native yeast had already started the process of consuming the sugars and converting them to alcohol, heat, and carbon dioxide. As the wine ferments, its “Beaumé” sugar levels are regularly checked.
After half of the sugars have been converted to alcohol, the producer stops any treading and lets the skins rise to the top of the lagar to form a solid layer. This deposit is removed using shovels and then pressed to remove any remaining wine, which is returned to the lagar.
The process that follows is called “mutage” and consists of adding brandy to the wine.
Adding Brandy To Port Wine
Yeast can survive in an environment with an alcoholic strength of less than 16% ABV. By adding alcohol to the wine, the yeast becomes dormant and ceases consuming the sugar. This process preserves high levels of residual sugar, which results in a sweet fortified wine.
To ensure that the brandy is evenly introduced to the wine, it is typically done while it is transferred to a storage tank. As the wine runs out of the lagar into a vat, brandy is slowly added to it as well.
Typically, a port wine will consist of 30% brandy in the final blend. For instance, Taylor’s Port uses a ratio of around 115 litres of brandy for 435 litres of wine.
Afterwards, the wine is left in the vats to rest until the following spring when it is transferred to the cellars or “lodge”. However, although the fermentation process has finished, it will require further ageing to properly develop.
How Port Wine Is Aged
Although all the different types of port are produced in a similar way up to this point, it mostly the ageing process where they begin to diverge.
Port is lauded for its qualities after extensive ageing. Therefore, producers have a legal obligation to sell no more than 30% of the wine after two year-minimum ageing period.
During the ageing process, port wine evaporates while in the barrel, which is known as the angel’s share. Compared to most alcoholic spirits, it’s quite low at just a 2% annual loss of liquid.
The local climate and the cellar’s humidity ensure that the alcohol and water evaporate at a very similar rate so the port doesn’t lose its strength. Meanwhile, the aromatic compounds, sugars, and acids do not evaporate. Consequently, long ageing results in a smaller albeit highly concentrated volume of wine.
Steel tanks may occasionally be used during the ageing process. However, as they are largely hermetic and inert, they are mostly used for storing rather than ageing the wine.
Some port wines styles such as Garrafeira may occasionally be stored in inert glass dame-jeanne or demijohn bottles. Although these reduce oxidative maturation, they don’t eliminate completely. Nevertheless, port wines that would suffer from further wood influence can benefit from this form of storage.
Meanwhile, the majority of port ageing primarily employs oak casks.
Port Wine Barrel Sizes
According to the flavours they wish to produce, port winemakers can choose between three different types of oak barrel:
- Pipa: 550 litres (145 US Gallons)
- Tonnel: 10,000 litres (2,640 US Gallons)
- Balseiro: 50,000 litres (13,210 US Gallons)
However, the above sizes are general approximations and aren’t standardised. Indeed, a tonnel can be as large as 14,000 litres while some producers may have balseiros barrels able to store 120,000 litres of wine!
Port ages through micro-oxidation as the wine comes into contact with the wood’s porous membrane. As a proportionally greater amount of wine will be near the edges in a smaller barrel, it will have greater contact with oxygen.
Therefore, winemakers will choose the barrel size according to the amount of oxygen they wish to expose to the wine. Particularly large balseiros will often have a limited effect and the wine will barely age, which is why they’re often used for ruby ports.
Meanwhile, smaller pipas will be chosen for more intense ageing. In most cases, the port will likely be transferred between several barrels throughout its ageing period.
Additionally, the barrels are rarely charred and winemakers will usually opt for older barrels to reduce the wood’s influence.
Port Wine Bottle-Ageing
Some varieties like vintage, late-bottled vintage, and crusted port will spend most of their time bottle-ageing rather than maturing in oak barrels. Although these types of port will begin ageing in oak barrels, they are eventually transferred to bottles.
However, rather than being fined and filtered, they are bottled with the sediment, which wasn’t extracted from the solid layer during fermentation. Therefore, the port will continue evolving even after it has been bottled.
In this case of vintage port, it will spend just two and half years barrel-ageing before being bottled. However, late-bottled and crusted ports may spend far longer before being removed from the casks.
You can learn more about which ports are aged using the methods above with our guide to the different types of port.
Blending Port Wine
After it has finished ageing, port wine is often blended to produce the final beverage. In most cases winemakers will combine different batches from several plots and locations. Given that these consisted of several grape varieties even during the initial maceration, they can already technically be regarded as blends.
However, ruby and tawny ports can also combine different vintages as long as they are older than the final age statement. As you will learn with our guide to the different types of port linked above, vintage varieties can only contain port wine from a single year.
How Strong Is Port Wine?
Port wine’s legal minimum strength is 17.5% ABV. However, it typically higher at around 20% ABV. Given the addition of a 77% ABV brandy during fermentation, it is far stronger than regular table wine.
Consequently, it is often consumed in smaller quantities when served.
Having now learned about how port is made, check out more of our resources on the fortified wine: