- Winter 1998 "Update" Newsletter Article -
New grape conveyor tried
Research specialist will compare wines made using "gentler" delivery systems
From CATI Publication #980101
Copyright © 1997. All rights reserved.
An enology professor at California State University, Fresno will conduct wine tastings this spring to learn if the use of a newly-designed grape conveyor system will ultimately help to produce a better quality wine.
Professor Carlos Muller, who heads enology research for the Viticulture and Enology Research Center at Fresno State, believes the new system he designed for use at wineries can handle the grapes more gently, preventing extraction of unwanted compounds.
The system is for use in the first stage of winery operation, when the grapes are brought from the vineyards by tractor-trailer rigs and dumped into hoppers.
The type of hopper used by most San Joaquin Valley wineries consists of a shallow "V"-shaped steel unit capable of holding a gondola-sized load of grapes (up to 25 tons). At the bottom of the hopper is a stainless steel dump-screw conveyor which pushes the grapes up to a stemmer-crusher or other juicing device.
While this manner of pushing the fruit is reliable and cost-effective, it also tends to crush the seeds prematurely, as the grapes often are pushed in and out of the screw several times during the conveyor process. "It has the inherent drawback of extensively juicing and macerating the grapes," Muller said. "A lot of the bitter compounds in the seeds are extracted into the juice prematurely."
Another method being tried at some wineries, and at Fresno State, is a belt conveyor system that carries the grapes rather than drives them. However, while being clearly more gentle, belts might wear out more quickly, requiring more service and bringing higher maintenance costs.
"In at least one case of a large valley winery, their experience with these belts proved unsatisfactory and they have since reverted to delivery by stainless steel screw conveyors – a rather extensive and expensive conversion," Muller said.
In his project Muller will attempt to achieve the "gentleness" of the belt conveyor system using a modified hopper design. The stainless steel screw sits at the bottom of a "U"-shaped trough at the bottom of the hopper. Muller hopes the design will pull the grapes more directly out of the hopper and reduce the amount of maceration.
Two lots of white wine are being made from French Colombard grapes picked this summer. One is from grapes delivered by a belt conveyor system (unit donated to the university by Westec – IRAPP of Healdsburg, California.); the other lot is from grapes moved by Muller’s newly designed screw conveyor.
Sensory and phenolic evaluations will be conducted this spring, with results to be released during the summer. Muller hopes to conduct the same comparison of conveyor systems next year using red wine grapes.
For details on this project, Muller may be contacted through VERC at (559) 278-2627.
{ page top }