Friday, 24 October 2014

Red, Red Wine

It is that point during harvest where we are nearing the end of our white grape intake and moving onto the red varietals in earnest. The daily routine has shifted from multiple press loads per day, and frantic racking. Now it's all about pump overs and plunge downs.

One of the fundamental concepts in the production of quality red wine is maceration. This means the extraction of tannin, flavour and colour compounds from the grape skins into the must. If this were not allowed to occur, you would end up with a greyish coloured wine with little flavour or structure. The degree of maceration that a wine undergoes can be somewhat controlled by the winemaker by manipulating two key variables:

1. Temperature
Heat speeds up the process of maceration by assisting in breaking down the cell structure of the skins and allowing the desired compounds (phenolics) to be released. Alcohol can have the same effect, acting as a solvent in which the organic compounds break down.

2. Skin Contact
It is up to the winemaker to decide how long the must will spend in contact with the skins. This can be anywhere from hours (for rose wine) to months, even once fermentation has been completed. This decision will be based primarily on the style of the desired end product.

Carbon dioxide generation from fermentation causes grape skins and other grape components to rise to the top of the must and form a 'cap' in the fermentation vessel. This results in limited skin contact, so mechanical methods are required to re-mix the must with the skins. 

Of course, in the world of romantics, this would all be achieved by gently stomping on the grapes.  Not quite the efficient method but I have, in fact, been doing some plunge downs which simply involve me sticking my arms down into the cap of the open fermenters and pushing down until juice comes up from below.

For larger quantities of wine held in stainless steel tanks, a pumpover is the most common method used for breaking up the cap. Basically, the bottom valve of the tank is opened up and the juice is allowed to drain into a collection tub, from which it is then pumped back into the top of the tank. This results in wetting or breaking up the cap and promoting increased contact between must and skins.

Besides conducting plunge downs and pump overs, my role in the lab requires me to regularly monitor the temperature and sugar level of the fermenting red must. This information is used by the winemaker to determine the regularity and length of the pumpovers based upon whether the wine is at the desired temperature and how well the fermentation is progressing. 

Sometimes the wine will be slow in reaching the desired warmth. We do have temperature control jackets on each tank, but when there are grape skins in the tank as well, they can limit the efficiency of the heat transfer from the jacket into the must. In this case, we need to conduct a rack and return whereby as much of the must as possible is drained out of the tank away from its skins and pumped to another tank. This tank is then set to warm to a certain temperature before the must is pumped back into the tank where the skins are waiting. Of course, this process is a luxury that can only be afforded if you have enough tanks in your winery!