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Refractometer calibration test kit developed

The Issue

San Joaquin Valley farmers rely on handheld refractometers to determine fruit maturity. A refractometer measures the percentage of sugar (ºBrix) in juice, allowing a grower to estimate a harvest date for a particular variety or field of grapes, peaches or melons. Often a refractometer is purchased and used year after year without being properly maintained or calibrated at the beginning of each season. A lack of calibration prior to each use can give faulty readings, leading a grower to think a crop is ready to harvest, when in fact it may be days or weeks away. Commercial refractometer calibration test kits are expensive and growers rarely purchase them. Additionally, the improper care and/or storage of refractometers will contribute to inaccurate readings. Proper calibration, use and maintenance of a refractometer will improve the accuracy and utility of sugar data in determining fruit maturity.

What Has ANR Done?

University of California Cooperative Extension farm advisors Stephen Vasquez and Shannon Mueller developed a simple calibration test kit and protocol for refractometer calibration, use and maintenance. The test kit can be easily assembled for under $5. The use and maintenance protocol will help preserve the integrity of the refractometer and ensure years of error-free service. Growers can download the article "Refractometer Calibration, Use and Maintenance," which describes each step in the process, at http://cefresno.ucdavis.edu/files/43066.pdf.

The Payoff

Refractometer calibration and maintenance improves accuracy of sugar data

Growers can easily make their own refractometer calibration test kit for relatively little cost, saving a grower roughly $100 to $200, the cost of purchasing a commercial test kit. The test kit and user protocol can be used for the entire season assuring growers that their refractometers will give them accurate sugar readings. The protocol for refractometer use and maintenance will give ºBrix data consistent with that collected by field scouts and packers.

Clientele Testimonial

"Hundreds of dollars have been saved by properly calibrating my company's refractometers at the beginning of the season using the UC Cooperative Extension protocol. By doing so, optimal fruit maturity is determined and harvest labor maximized." - Fresno County grape grower


Supporting Unit: Central Valley Region

Fresno County
Stephen Vasquez, viticulture farm advisor, sjvasquez@ucdavis.edu

Shannon Mueller, agronomy farm advisor, scmueller@ucdavis.edu

UCCE Fresno County, 1720 South Maple Avenue, Fresno CA 93702