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5 Tell-Tale Signs the Grapes Are Ready for Wine Harvest

Los Robles Hills Winery - A Real Wine Harvest

Wine harvest is a tricky time, but also a beautiful one. For a winemaker knowing when to harvest is a matter of taste, skill and awareness. A winemaker who notices more bird activity in the vineyard, for example, has just received an alert from Mother Nature that the grapes are ripe — the birds, raccoons and bears are always first in line for sweet fruit.

We’ll start off with a comment from wine club alumni Erik Miller, Winemaker/Founder Kokomo Winery in Sonoma’s Dry Creek Valley, who with winery partner and veteran viticulturist (40+ years among the vines) Randy Peters, selects that perfect moment of ripeness:

“Ripeness is essentially comprised of two parts. One part chemistry which includes sugars and PH and another part intuition which includes flavors from the Vineyard Brownness of the seed (lignification) and tannins of the skin. When Randy and I go into the Vineyard to taste the Vineyard we are first visually looking at the clusters to see if there is any shriveling or pucker, we then are tasting berries noting the crunch of the skin when we initially put it in our mouth, and then looking for complex flavors of black cherry instead of regular cherry or in whites more tropical flavors versus just green apple flavors. It takes several years to develop a palate for tasting sweet grapes. We only get one time a year to practice this palate and our mouth is competing with 25 brix of sugar which makes it difficult to taste the nuances that you are looking for.”

Revealing the 5 Tell-Tale Signs the Grapes Are Ready for Wine Harvest

As Erik indicated, all those seeking The Great Grape are evaluating it in several ways. These include, but aren’t limited to:

  1. Color of the grapes. Naturally, red grape varieties will gradually turn from green to red as they ripen. However, experienced winemakers know it could take many weeks, depending on the weather and the grape variety, before true ripeness sets in.
  2. Color of the stems and grape seeds: When ripe they will be brown.
  3. Added hints from grapes: They will plump up as sugars increase, and they will be easy to pull from a cluster the riper they get.
  4. Added hint from grape seeds: Taste a grape and the seeds are easily chewable when ripe. They are also brown.
  5. Flavor. Ripe grapes are sweet, with no hint of bitterness in the flesh or seeds. Experienced winemakers will look for the ultimate “varietal” flavors to show through.

In addition to this evidence of ripeness, winemakers also rely on technology to know when it is time to harvest the grapes. They’ll take a portable refractometer into the vineyard and measure sugar levels. The higher the sugar, the riper the grapes.

In the lab, they’ll look for pH and titratable acid (TA) levels. As grapes ripen, pH rises and acids drop. Both together give the winemaker an idea of the wine’s acidity.

What other concerns do winemakers have when they determine when its time for wine harvest? Here are a few shared with our wine club recently:

  • Quirks of the vineyard. Some rows ripen faster than others, depending on their sun exposure, altitude, exposure to wind, etc.
  • Type of Grape: Some grapes ripen faster than others.
  • Style of wine: If they are looking for terrific acidity, as in a Rosé, winemakers will be carefully watching those pH/TA lab reports.
  • Worker Availability: There may be a shortage of pickers that could delay harvest.
  • The Weather: Mother Nature may force a winemaker to harvest if she is threatening to dump a long period of cold rain, or, if temperatures keep rising and grapes are starting to dry up like raisins. Let’s face it — ultimately, Mom is in charge!

It’s time to enjoy wine harvest season, check out some local events in California’s wine country and plan your next getaway.

If you need help planning which wineries to visit, call The California Wine Club at 1-800-777-4443 or chat with our wine club Personal Wine Consultants online.

10 Responses

  1. Nancy Davison says:

    My dad 91, swears you have to wait until after the first frost. Anyone else go by that?

    • Karen D says:

      Thank you for the question, Nancy! I would never disagree with someone with that much life experience. I believe he may be talking about ice wine, as that is wine made specifically from frozen grapes. It is a terrific dessert-style wine. In California, winemakers who are not making ice wine usually have programs in place to prevent grapes from freezing when frost is expected. Cheers!

  2. Joyce Suske says:

    I’m new at growing wine grapes, not sure how soon to pick and what to do when they are picked. after crushing
    how you keep the juice unspoiled as you make the wine.

    • Karen D says:

      Hi Joyce,

      Congratulations on growing some grapes! What varietal are you growing? As a wine of the month club, we select wine from small family wineries to share with our members. We do not, ourselves, make wine. There are many resources online and in books that can answer your winemaking questions. Best wishes for delicious wine!

  3. Dear California Wine Club,
    I’ve been making wine for nearly 40 years and about 10 years ago starting growing wine grapes, with uneven success. I live in SoCal in Manhattan Beach, one mile inland. Best results so far are with Zinfandel but sugar content is low. Have just added mature Merlot, Pinot Noir, Cabernet vines and am hopeful for next year. How should the stems look as an indicator that the grapes are ripe? Also, what is the minimal sugar content for wine? I have a refractometer to check.

    Thanks in advance for your help!

    • Karen D says:

      Hi Arthur,

      Thank you for reaching out! Your wine growing project sounds very interesting and fun. Unfortunately, we do not grow grapes nor make wine, and therefore do not have the technical expertise you are looking for. The information we include in our blog posts about wine grape growing comes only from interviews that we do with artisan winemakers and grape growers.

      You may want to check out educational winemaking resources, such as those at U.C. Davis which has highly regarded programs related to wine:

      Best wishes to you for finding the technical winemaking resources you are looking for.


  4. Robert says:

    The bees and birds are taking mine before they are ripe enough for wine.

    • Karen D says:

      Oh no! In some vineyards, they put netting over the vines to protect the grapes from birds. We hope you get some grapes! Cheers to you, Robert.

  5. Victor says:

    If one side of the vineyard has grapes that are clearly ready, but the other side clearly not ready, is it advisable to store the ripe grapes while waiting for the others to ripen? – cool storage?

    • Karen D says:

      Hi Victor, We do not make wine ourselves, and so we are not the best source of information for winemaking. We are a wine of the month club with a focus on small, artisan wineries. I hope you find the information you are looking for. Cheers!

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