In Port winemaking perhaps the most important time during the fermentation is the moment when we end it and add the aguardente (grape spirit at 77% v/v) to the fermenting must. The aguardente we use is a pure grape spirit with neutral flavours and crystal clear colour – we want our grapes to define the character of our ports, not the aguardente. It is extremely important to get this right, not only to add the aguardente at the correct moment but also in the right amount.
If there is a mistake at this point a number of things can go wrong:
- If you add the aguardente too soon the wine will come out sweeter than intended and conversely if you add it slightly too late it will be drier. If you forget to add the aguardente at all – God forbid – because you overslept then you would eventually end up with a dry table wine. I have had nightmares about this before!
- If you add too much spirit you can end up with, for example, a wine at 21% (we prefer Graham’s Ports at 20% – oops), or if you add too little there is a risk that the fermentation won’t stop and the wine will continue to ferment to dryness unbeknownst to you.
The calculation is based on 3 important variables:
- Firstly, the number of Kilos in the lagar. With this we work out the number of pipes of grapes (1 pipe = 750Kg), and then multiply by 550 litres to get the approximate litres of must (In other words 750Kg of grapes give approximately 550 litres of must). Therefore 11000Kg of grapes/750 x 550 = approx 8066 litres of must.
- Secondly the initial Baumé or sweetness of the grapes. The riper they are, the longer they can ferment and the more colour, aroma, flavour we can extract.
- Thirdly the alcohol and final Baumé of the wine we intend to make.
With these 3 pieces of information we can work out using a set of tables and graphs when – at what baumé reading – and how much aguardente to add.
In practical terms we put the necessary amount of aguardente in the tank we use for fortification, and when the fermentation has reached the critical point – normally between 7º-8º Baumé – we add the fermenting must and pump over to mix them together well. The high-alcohol aguardente kills the yeast (thus ending the fermentation) and fortifies the wine to between 19-20% alc.
We always take a sample of must just before fortification that is sent to the laboratory for colour analysis. Using a spectrophotometer they analyse the red colour intensity of the wine which is then classified between A and F.
Samples of the finished wine are also taken for complete analysis. “Complete analysis” being one bottle for the lab and one bottle for us, usually! Visitors to the winery cannot resist trying the new wines.
The young Port is then transferred to the storage tank or tonel where it will spend the winter here in the Douro, before moving down to Gaia in the spring for long term ageing in our lodge in Vila Nova de Gaia.