The Effect of Application and Timing of Cryolite on Fluoride Levels in Red and White Wines

The main purpose of this experiment was to determine the level of fluoride in red and white wines from grapes sprayed with Cryolite at specific rates and application times. A four-year study at CSU Fresno has conclusively shown that Cryolite increases fluoride levels in red and white wines. From 1990 to 1993, many different rates and timing combinations were tried in order to clarify the role of Cryolite in wine fluoride. In 1993, a 6-pound full bloom rate was the basis for an application and timing trial tested on seven different vineyards in the San Joaquin Valley. The objective here was to determine the minimum Cryolite that would be efficacious and yet produce the lowest fluoride levels in wines. The experiment was conducted at 7 different vineyards in three general areas of the San Joaquin Valley. Zinfandel, Barbera, French Colombard, and Thompson Seedless varieties were studied (Table 1). At CSU Fresno, a replicated experiment was performed on Thompson Seedless, Zinfandel, and French Colombard. The treatment schedule is listed in Table 2. In addition, a second experiment focused on the role of surfactants with Cryolite on fluoride levels (Table 3). Treatments were applied at each vineyard using grower-supplied equipment; at CSU Fresno, applications were made with a single row over-the-vine boom sprayer. Insect populations were monitored frequently by growers and researchers during the growing season. No plots received applications of other non-fluoride containing products, but all other normal cultural practices were performed. At harvest, grapes from each treatment were made into wine. The wines were bottled and analyzed for fluoride by the Ion Selective Electrode method. The results from the 1993 research show that untreated grapes (Tl) had the lowest wine fluoride levels. In most cases, grapes treated at bloom and again 15 days later (T6) had the highest fluoride levels (Table 4). These results confirm earlier research that showed that wines which received Cryolite applications had significantly increased fluoride levels. The low rates applied at bloom, pre-bloom, and shatter caused small variations in fluoride levels, but the differences between treatments are very small. A replicated experiment at CSU Fresno showed no significant differences between any treatments (Table 5). In the surfactant study, applications of Cryolite with either a spreader or a sticker-spreader had no significant affect on wine fluoride levels. Most fluoride levels were exceptionally low in 1993, leading to the conclusion that the 6-pound full bloom rate will produce wine fluoride levels below the restrictive 1 ppm limit. Insect populations were monitored but counts remained low. No conclusions concerning efficacy can be made.