#40: When Should I Pick Those Grapes? Part One of Two
Aug 1, 2024
Why Two Parts?
Once I began to write about the timing of harvesting wine grapes, I quickly realized that there was simply too much information to squeeze it into a single 1000 word piece. Thus, two articles. Here’s the first:
Timing is Everything!
The most important decision I make each and every year is “When will be the perfect moment to pick that block of grapes?” and that choice will make a huge difference with the finished wine. What determines my choice depends on maturity of the grapes and the two primary factors that can help me determine that are the “Brix” and “pH” levels of the grapes.
What is “Brix”?
“Brix” is named after an 18th century German scientist, Adolph Brix, the first to create a set of standards to accurately measure the sugar content of a liquid. Brix simply means the amount of sugar (sucrose) in the grape juice. Why is that important? It is the sucrose that will ferment into alcohol during the winemaking process. More sugar = more alcohol. We want the grapes to ripen to a level of sweetness that is pleasing to the palate but won’t ferment beyond the desired percentage of alcohol.
What is “pH”?
Soren Sorensen, a Danish scientist, coined the abbreviated term “pH” in 1909 and it stands for the “power of Hydrogen” (don’t ask). What pH really means (remember high school chemistry?) is how acidic or basic a solution is. The number 7 is considered neutral; a number below 7 means more acidic and above 7 means more basic. Wine grapes at harvest are usually on the acidic side of 7 and the pH usually ranges from the low 3’s to the high 6’s (White wines are usually more acidic than reds. Thus, they have lower pH numbers.)
How do we evaluate sugars and acids?
The Old Way - Taste!
For thousands of years winemakers relied on tasting the grapes to figure when to pick. They would guess if the sweetness and the acidity of the grapes were perfect for harvest. Unfortunately, taste buds can vary greatly from person to person and can change depending on the food we’ve eaten, whether we brushed our teeth or had coffee, had a cold, or any number of variables. No two people will come up with the same conclusions when they taste but tasting the berries was the only way to evaluate whether the grapes were ready to be made into wine.
The Newer Way - Tools!
And then, some smart folks created two different tools that could tell us the exact levels of Brix and pH: the Refractometer and the pH Meter. Almost every winery, large or small, has each in the lab.
The Refractometer
A refractometer is a small, hand-held tool specifically used to test the level of sugars in the field or in the lab. It is a simple tool that only requires a drop or two of grape juice and very little training. There are two versions: the first looks like a mini-scope and shows the Brix level when viewed through the eyepiece; the second is a digital version. (We use them both but I prefer using the digital refractometer because my eyesight ain’t as good as it once was….
The pH Meter!
Just as important in evaluating grape maturity by using a refractometer to test for sugar is using a pH Meter to check the acidity of the juice. The tool is most commonly used in the lab but there are small portable versions that can be used in the field. (I prefer my lab version). We simply squeeze some grapes and put the juice into a small beaker. Once we have “standardized” the sensitive pH electrode, we stir the juice with the electrode, wait and let the numbers settle. The machine then shows a digital reading of the exact pH of that juice sample. Violá! I now have hard numbers for both pH and Brix!
Getting an Accurate Grape Sampling
The Brix and pH of the berries in any block of wine grapes can vary a good deal: one cluster of grapes at the top of a hill (where it is warmer) will probably be higher in Brix (more sugar) and higher in pH (less acid) than a grape cluster at the lower elevation. Sunny areas will yield different results than partially shaded areas. (Farmers usually will have designated the different areas in a vineyard and each will probably have a different watering cycle.) Each of those sub-areas in a vineyard is unique and should be evaluated independently for maturity. Randomly selecting and testing one cluster of grapes from somewhere in the vineyard would be a pretty subjective choice and not be a good example of the sugar and acid of the entire block. We need a more objective technique in order to get an accurate sampling and here’s how we do it:
With location-marked Zip Lock baggies in hand, we’ll begin walking the block between the 2nd and 3rd rows. We’ll stop at the fourth vine from the end on one side and stop where there is a grape cluster. We’ll pick the first two berries that we touch at the bottom of that cluster and they go into the baggie. Then we walk to the other side, skipping three vines and repeat, taking two more berries from the bottom. (No looking! There is a tendency to pick the best looking and plumpest grapes.) Then we repeat the process (skipping three vines each time) only this time picking two berries from the top of the cluster. We continue down the row, picking two berries each time but this time from the top of the cluster, then the outside, inside, front, then from the back. Then we repeat the process, starting again two berries from the bottom. When we reach the end of that row, we’ll move further through the block, skipping a row each time. Finally, we’ll reach the end of that block with a baggie full of grapes. When we finish with all the blocks, it’s off to our lab with our marked baggies, ready for analysis.
What Do You Do Then?
We’ve found that it’s best to evaluate for maturity by using a combination of both subjective (taste) and objective (tools) analysis. To do that we rely on a relatively technique developed in Italy a few decades ago called Berry Sensory Analysis.
Again, I am out of space, so my next article will explain in detail what that entails. When you are reading that article, we should be about halfway through our 2024 Harvest!
Wine Trivia: “Butt” was a Medieval unit of measurement for wine. A “Buttload of Wine” was about 475 liters (126 gallons).
Squire Fridell