Harvest mechanization revolutionized the California wine grape industry 30 years ago and created a war zone on many winery sugar stands.
It’s all over one three-letter word — rot.
Rot is a simple word with a complex definition. According to California Start University Department of Viticulture microbiologist Roy Thornton, rot is a complex mixture ofyeasts, bacteria and molds.
Rot impacts wine grape quality, and growers are docked if there is too much rot upon delivery to the winery.
When all grapes were hand harvested, grape clusters were sampled at the winery and the rot content was measured. The whole grape method requires an inspector to clip off rotten berries from a sample of grapes and express the weight as a percentage. With the advent of mechanization, however, a winery can have a sea of grape juice mixed with whole berries, stems and seeds among other things that has defied quick and accurate measurements for rot, according to Thornton. There can be 100 to 150 microorganisms in the juice mix, he told a Fresno State University Grape Day audience.
Thornton thinks the department has found a way to accurately measure mechanically harvested grapes at the winery.
Thornton and an army of students collecting samples from unharvested vineyards have discovered that a technology already in wineries can be utilized to accurately measure rot. It is Fourier transform infrared spectroscopy (FTIR).
FTIR accurately and quickly identified rot in Chardonnay and Zinfandel grape samples. This accuracy was evaluated by hand harvesting bunches from vineyards that were to be mechanically harvested within 24 to 48 hours. Thornton said the correlation between FTIR readings and hand-harvested Chardonnay bunches was exact. This season the model Thornton developed will be tested in 100 Zinfandel vineyards.
Thornton hopes in two years the FTIR method of measuring rot will be used by the wine grape inspection service, and the rot war will be over.