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Hand Refractometer

Hand Refractometer

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Usage conditions apply
This refractometer was used by winemakers at Stag's Leap Wine Cellars, in Napa Valley, during the 1997 harvest. Manufactured by Ty'mup Products, in Gardena, CA, this hand-held model is of the type commonly used to measure the sugar content of grapes and juice.
Judging when grapes are ready to pick is not as straightforward as it sounds. Winemakers consider many factors before giving the go-ahead for harvest, and determining the fruit's sugar content is critical. Because sugar in wine grapes is fermented into alcohol during the winemaking process, it is important to allow the grapes to ripen to a level of sweetness that is pleasing to the palate, but not past the desired percentage of alcohol.
While the senses of taste, sight, smell, and touch are the main instruments winemakers use, they also employ scientific devices to quantify their sensory perceptions. A hand-held refractometer is used in the field (as well as in the lab, during fermentation) to measure the "Brix" value, or the sugar content of the grapes. The user of the device presses a drop of juice against the glass plate, points it to a light source, and looks through the eyepiece. As light passes through the juice, molecules of the sugar refract the light on a scale, which assigns the sugar concentration a value. The measurement is represented by % Brix. For champagne grapes winemakers look for a reading of 19, for table wines between 21 and 24, and, for dessert wines, 27 or slightly higher.
Winemakers don't "pick by the numbers," (the Brix value) alone, but carefully observe and taste the grapes in advance of harvest. In California, grapes typically ripen in August and September, and this is when winemakers and vineyard managers can be seen in the fields fervently monitoring their crop. Ripening depends to some extent on the variety of grape, but there are many environmental factors that influence the way fruit matures.
Grapes planted on hillsides, for example, generally ripen more slowly than those on the valley floor because the rays of the sun are less direct and the vines are more exposed to cooling breezes.
As harvest approaches, winemakers begin tasting fruit from different parts of the vineyard. They sample grapes several times a day, a process described by Julia Winiarski, one of the winemakers at Stag's Leap Wine Cellars, in Napa Valley, during an interview with Smithsonian researchers in 1997:
When we go out to taste fruit we have an idea in our minds of what perfectly ripe fruit tastes like and looks like and feels like when you hold a cluster. And that's the form that all of the examples have to be compared to, all the different iterations or different versions of that form are overlaid in our minds when we're tasting and walking. Some fruit won't ever be there, they won't be that perfect cluster that we see, but it's [trying to get fruit] as close to that as you can.
Object Name
Ty'mup Products
Physical Description
glass (overall material)
plastic (overall material)
metal (overall material)
manufactured (overall production method/technique)
overall: 5 cm x 20 cm x 5 cm; 1 31/32 in x 7 7/8 in x 1 31/32 in
ID Number
accession number
catalog number
Credit Line
Gift of Warren & Barbara Winiarsky
See more items in
Work and Industry: Food Technology
Food: Transforming the American Table
Exhibition Location
National Museum of American History
Data Source
National Museum of American History
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