Thank you Rachael Ryan, Dustin Chabert, inderpal singh, and Patrick Miner for your responses last week to Cellar Conditions!
This week: Extended Maceration
Describe the process of extended maceration and what benefits or drawbacks it can provide.
Extended maceration generally refers to one of two processes--pre-fermentation cold soaking or post-fermentation extended maceration. In the former case, grapes are left to soak on the skins post-crush for an extended period (generally around three days) in a cool temperature-controlled tank, allowing for greater extraction of pigment. This ultimately leads to wines with greater color depth, but introduces an increased risk of bacterial spoilage. This technique is most commonly used for thin-skinned grapes, like Pinot Noir. In the latter instance, the wine is left to sit and soak on the skins post-fermentation for a (relatively) long period of time. This practice can increase the complexity of the wine, lengthen the tannin chains (making them more palatable), and increase its longevity and cellar-worthiness. However, this process generally removes color from the final wine, as a lot of the pigment can get reabsorbed into the skins during this period, and it runs the risk of accenting unripe tannins.
Can you run through the reasoning on bacteria spoilage on a cold soak. What temperature does the risk actually introducing spoilage pre-fermentation? How does this differ with a cold room vs a tank with glycol sheeting?
It's more of a risk with low quality or damaged fruit. The risk of bacterial spoilage and/or introduction of unwanted yeasts during cold soak is increased especially if the fruit has been damaged or compromised before being introduced into the tank. This can pose a problem, especially if the temperature isn't kept below 50 degrees. The risk can be mitigated by introducing a starter yeast culture at the beginning of the cold soak.
I can't speak for certain to the differences in the last part of the question, but I would assume that it has to do with the degree of accuracy with which the temperature can ultimately be manipulated and controlled.
Even with clean fruit, cold soak is a vulnerable time because of the high amount of available sugar in the tank, all of which a plethora of unwanted microbes would love to consume. Also, there's no CO2 yet being produced to inhibit fruit flies from feasting on the juice/berries. The lower temperatures could also favor wild yeast strains to begin to reproduce, and some of these strains produce VA. A healthy fermentation, with Saccharomyces cranking, will push away much of the competition.
A jacketed tank can efficiently lower the temperature quickly and to a precise number; likewise, it can rapidly be raised once the designated cold soak period is over. A small dose of SO2 will also help to inhibit any unwanted visitors until the temperature can be raised and the fermentation begins, and also, the tank can be manually layered with CO2 gas a few times a day.
All of that being said, however, I've never heard of anyone refer to a cold soak as extended maceration before. I guess it's not incorrect, but I've always thought of it as post-fermentation only, which is as explained above, mainly to soften tannins. This could also be a risky time, depending on length of maceration -- the wine can begin to oxidize, and also, it's once again exposed to fruit flies, etc. which can spread acetobacter, leading to VA.