Effect of Weather and Rice Moisture at Harvest on Milling Quality of California Medium-Grain Rice

Abstract

ABSTRACT. California's medium-grain rice industry experiences a wide range of head rice yield (HRY).he unit value of rice is based primarily on its head rice yield (HRY, the proportion of kernels greater than 75% of intact length; USDA-FGIS, 1994). Improving HRY is an ongoing goal for rice growers. The average moisture content of the paddy rice at harvest (HMC, expressed on a wet weight basis) influences HRY. For medium-grain rice grown in Italy, dry conditions allowed HMC to drop below about 15%, and a subsequent rain caused a significant drop in HRY (Finassi et al., 2002). However, when repeated rain events kept HMC above 20%, HRY was not influenced by HMC. In Louisiana, where rain events are common during rice maturation, long and medium grain rice experienced a significant reduction in HRY when rice dropped below 15.0% to 19.8% HMC depending on variety and year of harvest (Jodari and Lindscombe, 1996). A warmer and drier harvest season caused fissuring to begin at higher HMC than a cooler and more humid season. In two harvest seasons in Arkansas with numerous rain events, HRY was not affected by harvest moistures between 15% and 22% (Siebenmorgen et al., 1992).In California's rice production area, rain is rare and maximum HRY for medium-grain rice is obtained at high HMC. Kester et al. (1963) concluded that the highest HRY is obtained at 25% to 32% HMC. Morse et al. (1967) indicated that HRY peaks between 26% and 30% HMC. Geng et al. (1984) analyzed commercial data, and they concluded that high variability prevented them from finding a narrow range of HMC for high HRY and that HRY was maximum between 25% ±5% HMC. Commercial quality data for California medium-grain rice (D. Jones, Farmers Rice Cooperative, Sacramento, Cal., personal communication, 1999) clearly showed that HMC explains only a small portion of the variability in HRY, as described by the low regression coefficient for a second-order polynomial regression line ( fig. 1). While maximum HRY was obtained at HMCs above 20%, lots below 18% HMC had nearly the same quality, and lots above 22% moisture had HRY values of less than 50%. The data show that in commercial practice HMC was not a good predictor of HRY, and apparently there must be other variables influencing rice quality.A great deal of research beginning the 1930s showed that paddy rice kernels fissure when dried below a critical moisture content and then rehydrate because of exposure to free moisture or high humidity, (Kunze, 1993;Siebenmorgen et al., 1998;Lan et al., 1999). The fissured kernels break during milling, causing low HRY in lots with high amounts of fissured kernels. At harvest, individual kernels vary widely in moisture (Siebenmorgen et al., 1992), and if the pattern of moisture distribution varies because of varying cultural practices or weather conditions, the proportion of kernels below the critical moisture may be a better indicator of HRY than average moisture. Geng et al. (1984) indicated that cycles of drying and moisture absorption may influence quality, but they did no...

Three Quantitative Trait Loci Conferring Resistance to Kernel Fissuring in Rice Identified by Selective Genotyping in Two Tropical Japonica Populations

“…Cypress was novel among southern U.S. rice cultivars both for its high FisR and for its having a parent of California temperate japonica origin. Heavy dew formation can rewet and fissure rice preharvest and is common in the rice-growing region of California (Thompson and Mutters, 2006). Consistent with these observations is the theory that Cypress's novel FisR results from introgression of key alleles from its temperate japonica parent, 'L-202', into its predominantly southern U.S. tropical japonica genetic background.…”

“…Pinson et al (2012) used the aforementioned fissureinduction method to apply divergent selection, identifying both FisR and fissure susceptibile (FisS) phenotypic tails, within a Cypress × LaGrue F 2 population. Heavy dew formation can rewet and fissure rice preharvest and is common in the rice-growing region of California (Thompson and Mutters, 2006). During the progeny testing process, it was further noted that all of the most FisR F 2:3 families were semidarf in height (as is Cypress) while those further selected for FisS varied in height.…”

Moisture Diffusivity in Rice Components During Absorption and Desorption

“…Since the full-length grain is the preferred form of rice, such broken rice has typically lower market value. [2,3] Moisture diffusivity in food materials depends on its temperature [4][5][6][7][8][9][10] and instantaneous moisture content (MC). [11][12][13][14][15][16][17] In rice, temperature dependence of the diffusivity is well understood [4][5][6][7][8] ; however, few researchers have investigated its moisture dependence.…”

Combine Harvest Scheduling Program for Rough Rice using Max-coverage Algorithm

“…Correct harvest time considering prediction model of moisture content gives maximum harvest recovery, milled rice recovery, and head rice recovery. This reduces the cost of drying process and maximizes the farmhouse income (Kocher et al, 1990;Lu et al, 1994;Lu et al, 1995;Thompson et al, 2006).…”