As one of my vineyard manager co-workers famously says just about every other day whenever he answers a question like this, “It depends.” However, before I dive into all of the prevarications and provisos, here are some basic conversion assumptions for grape growing and wine production. These are handy facts to memorize so hopefully you can whip out the math at the drop of a hat when asked, or at least calculate them for yourself on the fly with (or without!) the help of your smartphone.
Let’s start with certain numbers which winemakers can count on.
• 1 bottle = 750 mL or 0.750 L
• 12 bottles = 1 case
• 1 case = 9 L = 2.42 gallons
• 1 barrel = 59 gallons = 223 L
Now let’s move onto some less certain numbers that will depend largely on where and how you farm and how you produce your wine.
Estimated vineyard yield
• High-production/low-value wine grapes: 7-10 tons/acre(15.6 -22.4 metric tons/hectare)
• Lower-production/higher-value wine grapes: 2-4 tons/acre (4.5 -9 metric tons/hectare)
I would say any home winemaker growing a hobby vineyard for themselves will most likely fall in the below (smaller yield) category.
Estimated Home Winery yield
• Red: 165 gallons/ton (0.69 L/kg)
• Whites or Rosés: 170 gallons/ton (0.71 L/kg).
Of course, this depends on so many factors. The smaller the berries, the lighter you press, the smaller-scale and less powerful your press, the lower your yield will be.
Wine Losses During Aging/Processing
Let’s say we should expect 2-4 percent of wine loss over the life of a wine. This loss will be lower with tank-aged stainless steel wines that are quick to bottle and will be larger with longer-aged wines that sit in the barrel and therefore evaporate more wine (the angel’s share) through the barrel over time.
Let’s take a conservative approach and assume you’ll get 3 tons to the acre (6.75 metric tons/hectare) of Cabernet Sauvignon with medium-sized berries and you don’t take a press cut. Your yield at the press will be about 155 gallons/ton (0.65 L/kg). That means one acre (0.405 hectare) of vineyard yields you 465 gallons (1,760 L) of wine. Assume 4% loss over the wine’s lifetime because you do 100% barrel aging. So pre-bottle, that leaves you with about 446 gallons (1,688 L) wine. Divide that by 2.42 and you get 184 cases, or 2,208 bottles of wine. So divide those bottles by your original 3 acres (1.2 hectares) and you get that your one acre (0.405 hectare) yielded you 736 bottles of wine.
You can play with the numbers and see how a swing one way or the other can change the result for better or worse. It’s best to look at all of the above criteria and do your best to put your own personal data into the calculations. If you can keep good records over a few harvests you’ll soon be able to more accurately predict exactly how many bottles you’re getting per acre of your own particular vineyard. Of course, the calculations are easier if you’re buying a specific number of tons from a producer, as opposed to just netting the produce from a certain number of acres. If you can keep your cellar well-humidified, you’ll also lose less volume over time. Each drop is precious, especially for a small-scale home winemaker.