grapesperbottle.jpgA visitor to the Grape Discovery Center posted a question on the Grape Discovery Center's Star Family Exhibit Room Comment and Question Wall: "How many grapes are used to make a bottle of wine?" Let's do the math and see what we come up with.

To answer this question, we'll start with the assumption that we are talking about a standard-sized bottle holding 750 mL (approximately 25 oz.). We'll also talk about a typical wine grape that is widely grown in the Lake Erie Grape Belt, Vidal Blanc. Vidal Blanc makes a very enjoyable white wine, typically with a touch of residual sugar. It is a French-American hybrid that was developed in France in the 1930's for Cognac production. The vine proved to be very cold-hardy and disease resistant, and as a result, is successfully grown in many cool-climate regions of the world, even as far north as Sweden.

Making wine from grapes is a fairly simple process: The grapes are harvested and delivered to the winery. The juice is then separated from the skins, seeds and pulp using a crusher/stemmer and press. The crusher/stemmer pops the berry open to allow the juice to flow out, and removes the berries from the stems. The crushed and stemmed fruit is put into a press to complete the process by squeezing the juice out of the berries. The juice is then transferred to a tank for settling and fermentation. 

Here's where the math begins. For this variety, we typically expect to get about 180 gallons of juice for each ton of grapes. Grape juice straight out of the press has a lot of fruit solids (bits of pulp, like you see in fresh orange juice bottles in the supermarket) still in it. Before fermentation is started, the winemaker will let the juice sit in the tank for a day or so to allow these solids to settle out, and the clear juice will be racked, the winemaking term for transferred, to a clean tank. Fermentation is then started and the natural sugar in the grape is converted to alcohol. We now have wine! The wine is racked a few more times to remove more sediment that may have formed during fermentation and aging, resulting in a very clear product.

All of this racking, though, means that we lose some of our original volume of juice and wine. In the end, it is more reasonable to assume that we will have 150 gallons of finished wine for each ton of grapes. So let's do some more math.

  • There are 128 oz. in a gallon, which means there are 19,200 oz. in 150 gallons (128 X 150)
  • A wine bottle holds 25 oz, so there are about 760 bottles in 150 gallons of wine (19,200 ÷ 25)
  • This equates to 760 bottles from 1 ton (2,000 lbs) of grapes.
  • Therefore, one bottle has the juice from 2.6 lbs of grapes (2,000 ÷ 760)bartlett.jpg

So, how many grapes are there in a pound? Good question, and one that is not so easy to answer. Grape varieties vary in the average size of berries they produce; some are large, plump berries; others are quite small. We really can't use a one-size-fits-all number for this—we have to look at the variety itself. In the case of Vidal Blanc, we're in luck! This past growing season, Jim and Darlene Bartlett, longtime wine-growers in North East, PA, did a study with Mercyhurst University looking at berry weight at different times of the growing season to be better able to predict crop yields (how many tons of grapes per acre of vineyard). One of the varieties they grow is Vidal Blanc, and one of the parameters they measured in this study was berry weight at harvest. Perfect! Using data from the study, we find the average weight of one Vidal Blanc berry is about 1.5 grams. Let's convert this to grapes per bottle:

  • 1 lb is 454 g, and we need 2.6 lbs of grapes, equalling 1,180 g (454 X 2.6)
  • A grape weighs 1.5 g, so 1,180 ÷ 1.5 = 

787 grapes in a bottle of wine! 

 

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