Wine Ed 411: Press Fractions

As the name of my blog is slowly evolving, I thought I would take today to introduce the topic of wine press fractions.  When wine, especially red, is fully fermented it is then sent to a wine press.  Many of you probably recognize the following basket press:

Photo from Google Images

The basket press is often used to press red wine (aka remove or separate the skins of the remaining grapes from the wine liquid).  When you first load up the basket press, a lot of liquid usually comes pouring off of the skins.  This is known as the free run, which means that you do not need to manually press the skins to remove the liquid.  After the free run is complete, or stops flowing, from the press, then a winemaker will begin to manually press the skins to remove any liquid that is caught in the grape matrix.  This action usually occurs in several steps, often increasing pressure in each step, and therefore creating a press run.

During wine pressing, a winemaker will decide whether to allow the liquid that is removed from each press run to be mixed in the free run, or separated into its own unique vessel, which creates a press fraction.  The wine world follows 2 schools of thought on this topic:

1) That mixing the free run with the press runs allows for better integration, chemical stability, and enhanced complexity of red wines, especially those that require several years of aging.

2) That separating press runs, especially in those years in which less mature fruit was harvested, allows for better control of the sensory impacts of the wine.  This is especially true with regards to tannins, or the compounds in wine that create bitter, astringent, and some body characteristics of the red wine.  As a winemaker continues to engage press runs, each subsequent run will extract more tannins, and therefore, add more bitterness, astringency, etc. to the final wine composition.  If the press runs are removed into their own press fractions, the winemaker has control to blend in press runs to their liking, and allow for better mouthfeel of the final wine.  The following diagram emphasizes the separation of press fractions.

Graphic by Author

As a wine drinker, winemaker, and wine educator, I can see the advantage of both processing techniques.  And actually, I can see that depending on region, growing season, grape variety, and state of the fermented grapes, a winemaker should be ready to use both options.  I cannot say that one technique is better than the other, as I've seen both processing methods used successfully to enhance the final quality of the wine.  But hopefully, this opens you up to a new part of winemaking that you never knew before... and it creates a fun new name for my blog.  :)