For the wine industry and wine enthusiasts alike, the most exciting time of the year is harvest season. The season when a year’s worth of passionate labor culminates into a hopefully abundant harvest. It can be stressful, intense, and exhausting, yet it’s a thrilling and joyous period in wine country. If you’ve never worked in a winery during harvest, then you might not be familiar with the ins and outs of how wine is actually made. So, let’s take a look at each step of the winemaking process
Around mid-to-late July in the Northern Hemisphere, winemakers, viticulturists, and harvest interns are diligently monitoring berry ripeness. The grapes have been growing for the past 6-8 weeks since fruit set. During this time, all grapes, whether they’re red or white varieties, start out green and hard.
Veraison is the point when grapes begin to ripen. It’s signaled by multi-colored grape clusters. For red wine varieties, the skins transition from green to red then purple. For white varieties, the skins become more translucent. During this time, the grapes are also growing in size and filling with water. Sugar levels start to rise and acidity levels drop. Tannins develop, and so do flavor and color compounds.
Now winemakers need to be on their toes to ensure grapes are picked at the optimum ripeness.
For sparkling wines, grapes are often picked a bit early to preserve a lot of that crisp, refreshing acidity.
Vineyard Sampling & How Winemakers Make Their Harvest Picking Decisions
Prior to actually harvesting the grapes, the winemaking team is out in the vineyards daily assessing the fruit. There are two main methods used to analyze grape maturity.
The first option involves relying on the sense to consider how grapes are progressing from veraison to maturity. Some questions in consideration during this process include:
- How thick/thin are the skins?
- Has the skin softened?
- Is the flesh separating from the skin
- Are the seeds green or brown (brown indicating ripeness)?
- How do they taste?
- Are they getting too much sun or not enough?
- Are the plants still healthy and looking good?
The senses can often tell you more pertinent information than lab results alone.
Additionally, vineyard sampling can be carried out for lab analysis. This process involves selecting a representative sample of grape clusters from the vineyard, i.e. picking clusters from various areas of a specific plot, and taking them to the lab to be assessed for the following among other things:
- Brix: the number of grams of sucrose per 100 grams of liquid. 1 gram of sugar converts to around 1/2 gram of alcohol. Generally, Brix x 0.59 gives you an estimated alcohol (but conversions range)
- Note that countries outside of America also use baumé, babbo and/or density (the latter of which is thought to be most accurate)
- pH: plays a critical role in different aspects of winemaking, most notably a wine’s stability. pH measures the strength/concentration of dissociated acids present and is calculated using the concentration of hydrogen ions.
- TA: titratable acidity, which gives an approximation of the total acidity (i.e. a measure of perceivable acidity. Total acidity on the other hand more accurately measures total acid content.)
Depending on the winery, the decision for when to pick for harvest is based on the results of lab analysis, what you saw/tasted/touched in the vineyard, or a combination of both.
Then, picking times are scheduled based on the weather and other factors.
Manual vs. Machine Harvesting
Once the harvest picking decision has been made, it’s go time baby! Grapes are often harvested in the wee hours of the morning before the sun comes out and the heat of the day arrives. The cooler temps help preserve acidity, aroma, flavors, and freshness once the grapes come off the vines.
You’ll often see wineries repping that their grapes are hand harvested (manual) because it’s often associated with higher quality wines.
Why? A more careful quality selection can be made in the vineyards when harvesting by hand. Grapes and clusters also arrive more intact. Plus, hand harvesting is generally gentler than machine harvesting and usually results in fewer broken grapes arriving at the winery, yielding a higher quality wine in the end.
I can definitely attest to this having processed manually harvested fruit and grapes harvested by machine. The machine harvester shakes the vines in order to harvest the clusters. But the process is rough and also brings along a lot of leaves, twigs, rocks, bugs, and even little critters.
Manual labor is expensive and for many mass produced wines, simply not a feasible or practical solution for the sheer volume of grapes that need to come off the vines. Moreover, there are several high tech machine harvesters that deliver a better quality harvest with more precision. It all depends on what the winery or grower can spend on labor to harvest their fruit.
The size of the containers the grapes are transferred from vineyard to winery in is another factor to consider. Bigger containers mean more weight on the grapes towards the bottom and grapes can get smashed or damaged. Smaller containers mean the weight is more evenly dispersed. So many decisions to make all in the name of quality!
Fruit Processing for White Wines
So, the grapes arrive at the winery, now what?
Well, if it’s the first fruit of the season, a special bottle of something is traditionally popped to bless the harvest.
For white wine, steps for processing grapes typically go like this:
- The grapes are sorted at the sorting table.
- Then de-stemmed or left whole-cluster depending on the wine/winery.
- Crushed (or not).
- Then put directly into the press. This can be done via manual labor, forklift, conveyor belt, or using massive pumps and piping if at a more industrial winery.
- Pressing is done with a basket press or bladder press, the latter of which squeezes from the center of the press outward so most of the fruit receives the same amount of pressure. The juice is tasted often during pressing to avoid over extraction.
- Must is then pumped into tank for fermentation.
Fruit Processing for Red Wines
For the red winemaking process, grapes are:
- De-stemmed (or not in the case of whole cluster fermentation)
- Crushed by machine or using your feet!(or not for carbonic maceration)
- Wineries with big budgets might also have an optical sorter, which uses a computer and camera camera to remove any unwanted berries per programmed dimensions for the variety. Yes, it’s cool!
- Must is pumped or dumped into tanks for fermentation
- SO2 is added at crushing
- Option to cold soak prior to fermentation: Must is kept at low temperature while soaking for enhanced extraction of anthocyanins and aroma/flavor compounds
White Wine Fermentation
Now it’s time to talk about the most important part of the winemaking process that turns grape juice into our beloved wine. It wouldn’t be possible without magical little yeast that consume sugars, turning them into alcohol. Plus carbon dioxide and some other byproducts, too.
This is the most complex part of winemaking. So, let’s keep it simple for this post with a few winemaking considerations around fermentation.
Spontaneous Fermentation vs. Yeast Inoculation
All grapes have yeasts naturally on their skins and there are yeasts in the winery, so fermentation will begin spontaneously. Some winemakers may choose to inoculate with yeast cultures to start fermentation or for desired effects certain yeast strains may have on a wine.
Fermentation Vessel Selection
Winemakers can choose from a whole range of vessels for fermentation. Steel tanks are the easiest to clean while concrete tanks or concrete eggs allow for the tiniest bit of micro-oxygenation. Oak barrels and even amphorae both give a softer, rounder mouthfeel and texture.
When it comes to white wines, stainless steel tanks are generally used for a fresher style. These vessels are also most ideal for temperature control. Barrel fermentation is frequently used for wines like Chardonnay where producers may want a richer, rounder, more full-bodied style.
Unlike red wines, white wines are not fermented on the skins. Except in the case of orange wines or amber wines, in which case there is some skin contact which gives those wines their color, texture, and pleasant tannins.
Red Wine Fermentation
Similar to the white wine fermentation process, red wine fermentation generally begins with two main decisions:
- Spontaneous fermentation vs. yeast inoculation
- Fermentation vessel selection
Red wine fermentation differs from white wine fermentation in that red wine ferments on the skins, which is where red wine’s color comes from. This is where cap management comes into play.
As CO2 & heat are released during fermentation, the grape skins are pushed to the top of the wine, forming a cap. This cap of grape skins needs to be pushed down and circulated within the fermenting wine for better extraction of color, flavors, tannin, etc. Cap management techniques also prevent spoilage bacteria from forming and to introduce some oxygen, which during fermentation plays a significant role in softening wine, while also minimizing the risk of flaws taking hold. These are the 3 main techniques:
- Pump overs are a bit more gentle, taking juice from the bottom of the tank and pumping it back over the cap. Generally, pumping over the full volume of the tank daily helps to maximize extraction.
- Punch downs involve using a punching tool to break up the cap and displace the solids into the fermenting liquid.
- Rack and return, also known as delestage, is a third method used to extract color without producing harsh tannins. But it takes more time, as the wine is racked to a separate vessel or tank to rest briefly before being pumped back over the grape skins in the original fermentation vessel.
Delestage gently extracts the desired compounds from the wine, aerates the wine, and provides brief periods of time for the free-run juice to ferment apart from the skins.
Pressing Off Tanks, Free Run Juice & More
So, fermentation is complete. Now what?
For white wines, the tanks are drained and the wine is racked (or transferred) into barrels or into another tank. Lees, which are dead yeast cells and other solids, have settled at the bottom of the tank by now. So the tank is drained from a racking valve that sits higher than the bottom of the tank to avoid pulling all the lees with the wine. Once drained, the door to the tank can be opened and out come the lees.
Sometimes the fine lees are kept on the wine for added texture and complexity. These lees are smaller particles than what are known as the gross lees. During bâttonage, the wine is stirred up every so often to circulate the lees.
For reds, the wine is similarly drained out of the tank. A hopper is placed below the lower valve to catch the grape skins that have escaped. This wine is called the ‘free run’ juice for obvious reasons.
Once drained, the tank door is opened and it’s time to dig out the tank! First from the outside, pulling the pomace into bins. Then, once you’ve cleared enough space and opened the tank from above for air circulation, it’s time to climb in! Trust me, this is hard work. All of the pomace, or the left behind grape skins and solids are then dumped into a press like the basket press pictured here.
The pomace is pressed and that wine is typically kept separate from the free run for aging. It tends to have higher tannins from more extraction.
What Happens After the Grape Harvest?
Once wines are racked off of tanks and pressed, they’re pumped into stainless steel tanks, concrete tanks, barrels, or wooden vats for aging.
They’ll later be blended if needed. Then, when the time for bottling approaches, the wines can be:
- Fined for clarification and stabilization. Fining involves removing unwanted material from the wine using a fining agent like bentonite (used widely in white wines), egg whites, gelatin, or isinglass. The agents attract the unwanted particles in the wine so they are big enough to filter out.
- The filtering process provides microbial stability and gives the wine a more polished aesthetic.
When Is Harvest Season in Wine Country?
The timing of harvest season depends on whether you’re in the northern or southern hemisphere. In the northern hemisphere, harvest generally starts around late August and ends in October or November. Whereas the southern hemisphere kicks off the season in February and finishes in April.
Ready to Learn More About Harvest?
Check out these blogs about covering my first harvest and winemaking experience in Paso Robles, California.