In the Winery
Tannins and astringency
There’s a “sweet spot” for every vineyard and grape variety, and it typically takes years of trial, error and observation to find it. By Gary Strachan
ince my vineyard article dealt with phytoalexin management, it seemed to be a natural extension that I should deal with tannin management for winemaking. Wine tannins are developed in the vineyard under the control of the vineyard manager. They are one of the arsenal of phytoalexin-induced compounds that protect a grapevine from a wide range of problems. Tannin composition and level varies among grape varieties. Site selection determines whether a given variety can ripen tannins before harvest. Crop load affects tannin quality and pick date. There’s a “sweet spot” for every vineyard and grape variety, and it typically takes years of trial, error and observation to find it.
The seat-of-the-pants method to assess tannin quality is to examine berries by sight and taste before picking. Are the seeds green or brown or some shade in between? For most wines, the browner the better.
Varietal character is created by secondary metabolites at about the same rate as seed tannins mature, so pay attention not only to the berry colour but also chew the seeds to detect the level of astringency.
If the astringency is drying and puts an edge on your teeth, leave the grapes to hang. Skin tannins typically are not so drying as seed tannins. When the berries are ready for harvest, the skins will taste fruitier and the tannins will be less drying on your palate. Fully developed skin tannin and colour will enable wines to age better, will impart better colour and mouth feel to the wine, and will soften the perception of acidity (sourness).
Extended hang time has its own problems. The sugar may become
excessively high, the berries may start to shrivel, and/or the pH may climb to a level that makes it difficult to retain fruitiness in the final wine.
The simplest extraction is to destem and crush the berries. For overmature grapes, it may be best to whole cluster press to minimize tannin extraction.
If you want more tannin extraction, to enhance mouth-feel and fruit in
A photo of (mostly) mature grape seeds. Accepted wisdom is that the colour of grape seeds relates to tannin character in wine, but that opinion is controversial among winemakers.
white wines, they can be held in cold maceration with or without pectinase for, say, overnight before you press. If you are more adventurous, you can make “orange wine” by starting the fermentation with white skins, as you would for a red wine. You can press when you feel you have attained enough tannin to bring up the mouth feel. This practice isn’t recommended for the faint of heart or a for batch with immature tannin. If you mess up, it’s tricky to fix. Red grapes can be whole-cluster pressed (especially useful if they aren’t mature) and can be made into rose or blanc de noir wines with low tannin content.
If you want to enhance the colour and tannin content of a red wine, then destem and crush the berries, and drain off some of the free-run juice for use as a rose or blanc de noir. The remaining skins and seeds will be a larger proportion of the must and will contribute a higher level of colour and tannin than could have been obtained from the original berries.
The classic strategy for tannin and colour extraction in red wines is to start the fermentation in the presence of skins. I like to layer yeast on top of the skins rather than mix it into the must. This assures that the yeast will have enough oxygen for rapid growth during fermentation establishment. Yeast will stop growing when the fermentation becomes anaerobic.
When the yeast starts to grow, it will
form a creamy layer with bubbles around the edge. It will then sink and the fermentation should start to take off vigorously, dependent on temperature.
A strong fermentation will likely require three punch-downs per day to submerge the floating skins. Mixing is important for colour and tannin extraction. It is also essential to prevent vinegar bacteria from growing in a dried-out cap that becomes aerobic. There is a fine line between enough air and too much. Carbon dioxide from fermentation is denser than air and excludes air by displacement, but oxygen is required to produce aldehydes that assist with colour development of red wines. There are a number of ways to provide air/oxygen but one of the best ways is delestage . This requires a spare tank, used to pump the must from one tank to the other instead of punching the cap. This method aerates the must more completely and drives off much of the dissolved carbon dioxide. The result is usually a red wine with softer tannins and better colour than can be obtained by a punch-down. The many ways in which colour can be developed in red wine deserves a lot more discussion, but the message here is that care in the vineyard can lead to consistently high quality if you pay attention to berry development throughout the season.
British Columbia FRUIT GROWER • Fall-Winter 2017
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