Cellar talk: Post harvest through spring [or fall] bottling – Part 2

Harvest in Wine Country is complete, except for those grapes still left on the vines for the Ice Wine harvest.  A couple of weeks ago, this column shared stories about what happens the first few weeks in the wine cellar.  It ended with what happens on the crush pad into fermentation tanks.

This covers cellar happenings from Crush through mid to late winter.

Once the juice is safely in tanks and barrels, a whole series of cellar activities begin in earnest.  Through every step, the cellar teams are attentive to each barrel and tank, making copious notes and often posting comments on the vats themselves.

Sometime soon, several white varieties and many of the reds go through a process known as ‘malolactic fermentation.’  Malolactic fermentation (ML) is a process where the harsh, natural malic acid (think Granny Smith apples) in the juice is converted into softer lactic acid (think milk), reducing overall acidity, and helping to manage the pH levels. The result is a smoother, more stable wine and especially in white wines, by adding a ‘buttery’ under tone. 

It is most used in red wines like the Cabernets and Merlot and in more complex whites like Chardonnay.  It is NOT used in fruity, higher acid wines like Riesling or Sauvignon Blanc to not reduce their charm. The process is usually slow and will take a couple weeks or even a month or more. Throughout the season the ‘cellar rats’ and the head winemaker continue to monitor progress for appropriate levels of pH, even temperatures, and alcohol levels.

During the balance of the winter, the team then works on ‘clarification’ and ‘cold stabilization.’ The objective here is to remove remaining solids [by ‘racking’ or transferring from one container to another], using ‘fining’ or clarification agents [sometimes bentonite or egg whites] and then dropping the temperature in each tank to about the freezing level to remove tartaric acid.  Tartaric is another of the natural acids in wine and without this cold stabilization process, when wine is chilled in a customer’s refrigerator before serving, these ‘tartrates’ [they look like crystal snowflakes] will form and collect in the bottom of a bottle.  They are harmless but obviously are not attractive when poured into a glass on a dinner table.   

In most cellars, the next step will be filtration.  When wine is filtered, it's pushed through numerous filter plates with pads that have tiny pores to remove yeast, bacteria, and sediment. The finished product is cleaner, more stable and prettier in a bottle. Filtration prevents cloudiness, but most importantly prevents off-flavors and prevents any re-fermentation in a bottle.  If wine is not carefully filtered, refermentation may occur.  The bottle will leak, corks will sometimes pop unexpectedly, resulting in ruined carpeting in homes and giant messes on retail floors and shelves [after which the winemaker will likely lose the opportunity to ever sell to that retailer again]. Again, attention to detail is critical, as too tight a filter process can strip subtle flavors, and much appreciated aromas. It can ruin the quality of even the best wines grown in an exceptional harvest season.

More in part three on ‘Cellar talk’ soon.