Grapes across San Luis Obispo County — plump and ready after months of ripening — are being plucked from the vines and brought into wineries to be crushed and fermented into wine.
It’s harvest season, a busy — and critical — time for the county’s 200-plus wineries.
“We only get one chance every year, so we have to get it right,” said Drew Nenow, enologist at ONX Wines, who took time from the hectic harvest schedule to lead a weekend “farm-to-glass” tour of the winemaking process with ONX associate winemaker Jeff Strekas.
The journey starts with the key decision on when to pick the grapes. Pick too early and you won’t get good flavor. Pick too late and you risk winding up with too-high alcohol levels or losing grapes to rot, raisining or inclement weather.
“When to pick has the biggest singular effect on the end product,” Nenow said.
The decision is informed by a couple of empirical tests: pH, a measure of acidity, and Brix, which measures sugar content. Standing in ONX’s 50-acre vineyard on 120 acres on the far west side of Templeton off Bethel Road, Strekas and Nenow demonstrate the bag-smashing test.
They collect berries from various clusters around a vineyard block, crush them up in a plastic bag, pour the juice onto a small device called a refractometer and hold it up in the sunlight to get a Brix reading.
But the main determination is simply by taste. Experienced winemakers can pop a berry in their mouth, let the juice dissipate, spit out the seed and chew on the skin — where much of a wine’s flavor comes from — to tell if it’s ready. They’ll also check that the seeds have developed their coat, turning from neon green to brown in a sign of maturity.
When the grapes are ready, picking crews are brought in, which at ONX means up to about 12 people per shift.
Picking begins at the coldest part of the night — 3 a.m. or so — to keep the fruit as chilled as possible until it gets into the winery, preserving acidity and preventing fermentation from starting.
“We want them to come into the winery nice and cold, with no berries breaking,” Nenow said.
A tractor towing a trailer topped with three half-ton bins inches slowly between vineyard rows, followed by a crew of about four workers who clip clusters off the vine and toss them into the bins.
As the bins are filled, they are swapped for empty ones and loaded onto a truck that delivers them to ONX’s production facility up the road in Paso Robles’ Tin City complex. Once there, red and white grapes go their separate ways.
White grapes go out back, where they are dumped into a bladder press. The pneumatic bladder inflates like a balloon, pressing the grapes against a metal cage, squeezing the juice through slots and leaving everything else behind.
The juice is transferred into stainless steel tanks, where it’s inoculated with yeast to spark the fermentation that over 10 to 21 days transforms the sugars into alcohol.
Red grapes go into the winery, where a conveyor drops them into a destemming machine that uses a back-and-forth shaking motion to separate the grapes from the stems.
“When grapes are ripe, they’re about to fall off the stems anyway,” said Nenow, noting that any dried-out fruit is more likely to remain on the stems. “It flings out the stems with raisins still attached, so we don’t have to do as much sorting.”
The fruit then passes onto a shaker table, where the movement and one or two people sort out any immature shot berries, moldy raisins or MOG (“material other than grapes”) by hand, while any juice that’s escaped is captured for reuse or discarding.
The resulting mixture — partially crushed grapes, juice, skins and seeds called must — travels up another conveyer and into 1,000- or 2,000-gallon stainless steel tanks. As fermentation gets underway, carbon dioxide pushes the solid material to the top, creating a 2- to 12-inch cap of skins.
To extract the color and flavor from those skins, ONX winemakers pump juice from the bottom up over the cap a couple times a day in what’s called a pump-over. On a smaller lot, they may use a similar technique called a punch-down, in which someone stands over the tank and breaks up the cap with a long metal tool.
Once fermentation is complete, the solid part of the must, called the pomace, is run through a basket press to squeeze out every last drop of juice. That’s then combined with the rest of the nascent wine headed for a long sleep in a barrel (about four months for whites and 12 to 20 months for reds) before being bottled and released for consumption.
It’s a basic process, winemakers say, but one that rarely goes the same way twice, what with differences in growing seasons, variation among varietals, sometimes unpredictable fermentations and the occasional equipment malfunction or human error.
“Winemaking is an interplay between romantic, philosophical ideals and logistics,” Strekas said.