Around the beginning of September, I asked Jason Gerard, our associate winemaker who also happens to be a good writer, to write a blog about what was happening in the vineyard.  Just looking out the window, I could see the lush green of our Kerry’s Vineyard but what was going on under those canopied rows?  Here’s what he had to say:

A walk through the vineyard reveals grape clusters with a mosaic of green and purple berries. Just how many of these berries are purple gives us a good indication of how far away we are from harvesting the fruits of our labor. Of course every vineyard is at a different stage in its grape maturity as many factors play into when a grape will be ready to be picked. Location, varietal, rootstock are just to name a few of the variables that makes every vineyard block unique and therefore each will have a different optimal day for harvesting. For example, at the same vineyard location, on nearly identical soils, we have a block of Cabernet Sauvignon that is 100% through veraison (the word used to describe the coloring process of the grapes from green and immature to purple and mature) and another block right

Cab grapes in Kerry's Vineyard

Veraison in early September

next to it of Petit Verdot which is at 75% veraison. This tells us as winemakers that the Cab will be picked before the Petit Verdot. This of course helps us in our logistical planning for the harvest. Multiply this many-fold and you begin to understand the complexities of planning something that is as dynamic as the grape harvest.

At Tom Eddy Wines, we bring in fruit to the winery from several different vineyards from all over Napa Valley. At this time of year we are constantly traveling to all these vineyards to assess the current status of grape maturity. There are several ways in which we do this both scientific and instinctual in nature. The most obvious way of determining berry ripeness is through the good old-fashioned taste test. However, we also like to take a more scientific approach by testing some basic berry chemistry in the Tom Eddy Laboratory or what some commonly refer to as the kitchen….

How this works is, Tom or I will randomly select approximately 100 berries from any given vineyard and bring them back to the kitchen, which, literally is a kitchen but with a few not so common kitchen upgrades that allow me to do some basic chemistry. The 100 berry sample is crushed and the juice that is produced is collected in a beaker. There are three different numerical values that are obtained from this juice sample that give us insight into the maturity level of the grape: brix, Total Acidity and pH.

Cabernet ripening in Kerry's Vineyard

Maturing grapes in Kerry's Vineyard

As a grape matures to ripeness, it accumulates sugar through photosynthesis. The amount of sugar accumulated is measured in Brix. Using a refractometer, a couple of drops of the crushed sample juice are placed on the lens of the device. Based on the density of the juice, the refractometer will display a brix value which is very similar to percent sugar but based on density. Once the brix value is around 25 (not exactly 25% but very close), we know the grapes have accumulated enough sugar to be considered ripe for the picking. However, two other factors are also evaluated as brix does not tell the whole story.

The Total Acidity and pH values are closely related and also give great insight into grape maturity. As a berry matures the total acidity level drops. If you ever get a chance to try an unripe grape, you will notice an intense sour quality. This is due to a high level of total acidity and makes the grapes at this stage, almost unbearably sour and inedible. However, as the acidity drops and the brix increases due to sugar levels increasing, these two ripening factors come into balance. The key to picking the fruit at the right time is all based on the right balance of sweetness (determined by brix) and sourness (determined by Total Acidity). This is why it is so critical to check the vineyards constantly at this time of year because the chemistry within the fruit is constantly changing and evolving towards ripeness and picking the grapes within the right window of time can mean the difference between amazing wine or unbalanced wine.

pH is the final test to determine the acid level and therefore the maturity level of the crushed grape juice. This test is based on the total number of Hydrogen ions in the juice which is an inverse logarithmic scale so as the Total Acidity drops, the pH value goes up. In general the pH range for ripe Cabernet is between 3.50 and 3.80. (As a frame of reference, Hydrochloric acid is very acidic at about pH 1.0 and our stomachs are also quite acidic at 2.0. Water is generally neutral at pH 7.0)

So as the floor and counters of the Tom Eddy kitchen laboratory get sticky with the analysis of grape juice, we know we are inching closer to that fateful first day of harvest. Are we ready for the logistical chaos that is harvest? Of course we are! This is what we live for!                                            Jason

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