Wood and its influence on Port style

[Roy Hersh]

The simplest way to understand Port wine is to divide the categories between wood-aged and those that require aging in bottle. For those just learning about Port, you can find which categories fall into wood-aged vs. bottle-aged Port, in our FAQ section (on the homepage).

What I'd like to briefly explore, is why there is a difference between the size of the wooden vessels used for aging the two main styles of Port.

Wood-aged Ports tend towards aging in smaller wooden casks, known as Port "pipes" which tend to hold around 500 liters. This allows for a greater surface area of wood to be exposed to a rather small volume of Port wine. This is essential to enable the ruby color to turn more to a tawny or amber hue, the longer the wine remains in contact with the wood. It also allows for a good amount of evaporation and provides the Port with nutty nuances and flavors that include figs, prunes, raisins, caramel and marzipan.

Conversely, bottle-aged Ports begin their lives in extremely large wooden vats (that can be oak, chestnut and other hardwoods) that can vary in size up to tens of thousands of liters and occasionally even reaching hundreds of thousands of liters of Port in a single vessel. The large volume of Port has minimal contact with the small surface area of wood. Evaporation is much less prominent in these containers. Additionally the color remains robust and bright ruby as the wood does not leach out the anthrocyanins (a compound which contains the pigmentation of the grape). The flavor profile also stays far more vibrant and youthful with primary red and black berry flavors along with plum and currants.

We can discuss the names and sizes of the wooden vessels used for aging (like Hogshead, Lodge Pipes and Tonnels for example) if there is further interest.

[Frederick Blais]

Roy, what do you think in % is the impact of oxygen vs wood for flavours and color component of a Port?

My understanding was that those old pipes used for Tawny for example were quite neutral not giving any flavours but mainly providing a vessel to make contact with oxygen which was altering the color and the flavours.

I can assume that a few producers might introduce younger barrels to boost flavours, but I have not withness it from my eyes yet.

[Bryan Robinson]

Roy, what do you think in % is the impact of oxygen vs wood for flavours and color component of a Port?

If no one minds, I’ll take a crack at this one.

In color, there are many things going on, but none of them have anything to do with the wood as far as I know. Monomeric Anthocyanins, the grape pigment, aren’t very stable, and really only provide color for very fresh wine. Most wine will lose over 90% of its monomeric anthocyanin content in the first 2-3 years, even if aged in stainless steel. Most of the pigment of mature wine is made up of polymers. Sometimes the monomeric anthocyanin gets bound up and precipitates out of solution with the yeast. It can also react with other compounds to form stable polymer pigments, or colorless compounds. The single best indicator of which reaction is going to take dominate is the amount of unbound aldehydes in solution. Aldehydes are oxidized ethanol. And there we are back to oxygen.

There is a scientific paper that goes into greater detail:

J. Bakker, and C.F Timberlake. The Mechanism of Color Changes in Aging Port Wine. Am. J. Enol. Vitic., Vol 37, No. 4, 1986
http://www.ajevonline.org/cgi/reprint/37/4/288

While I don’t have any papers to back this up, the frequent racking of wood aged port might actually have a more pronounced effect than barrel size. That might be fun to test someday.

As for the aging reactions that effect flavor, I’m not quite there yet. It is a complete coincidence that I happen to be working on a paper that is an off-shoot of this question. It has to do with the concentration effect of barrels being duplicated by reverse osmosis filtering. As I am not submitting it until mid-June, it has been back burner for me, but I hope to be up on the subject over the next few weeks.