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V. Factors Affecting Qualities of Rice |
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Most people refer to the USDA grade sheet in referring to the different qualities of rice. The degree of milling, percentage of damaged kernels, and percentage of brokens are all important factors. But all rice that meets a US #1 grade is not the same (not even close), and from this point on the issue becomes much more complex. There are many factors that effect taste and texture, and this section will try and address most of those. Sage V Foods has a great deal of knowledge in this area that is proprietary and will not be disclosed in this document. The USDA grade system and a US #1 grade. Go to United States Standards for Milled Rice for all the gory details of the different grades of rice. A US No 1, grade of long grain rice meets the following criteria:
Package Quality Rice. In the US almost all rice sold to the consumer is of a higher quality than rice meeting the minimum requirements of a US #1. Each mill has its own standards for its package quality rice, but in general the improvements are made in the areas of milling degree and damages. Package Quality rice has a much harder milling degree and so the rice is whiter and cleaner tasting. Package Quality rice usually has fewer damaged kernels and impurities such as weed seeds and paddy. Milling Degree. Milling degree is an important factor for quality. Milling removes the bran layer. Rice bran is about 20 % oil and also is subject to very aggressive enzyme activity. Once the structure of the bran is disrupted lipase enzyme attacks the oil and creates free fatty acids. The bran becomes rancid very quickly. Any bran remaining on the rice affects the taste. Milling the rice very hard improves whiteness and flavor. Broken Rice. Broken rice gets soft and mushy when cooked. From a nutritional standpoint, brokens are the same as whole grain. But the texture is poor and brokens tend to have more bran, which affects flavor. Impurities. Obviously weed seeds, paddy rice, and other impurities affect the appearance of the rice. Small weed seeds like water grass can go unnoticed, but affect the flavor when cooking. In California, adobe balls (hard balls of clay) and often stones get in the rice. The USDA system does not properly account for adobe balls and allows many to be in the rice. Nature of Starch. This is a very complex area and there is still much to be learned. The nature of rice starch differs depending on variety, growing area, and crop year. The nature of the starch affects texture and retrogradation properties of the rice. Most people knowledgeable about rice have heard of amylose and amylopectin. These are two different types of starches. Amylose is a long chained starch without a lot of branching (like a pine tree), and amylopectin is a shorter, but much more highly branched chain of elements (like an oak tree). Indica type long grain rice has 22 percent amylose and 78 amylopectin. Japonica medium grain rice has 18 percent amylose and 82 percent amylopectin. In general rice with more amylopectin is softer, sticker, holds moisture better, and is more resistant to retrogradation. The amylopectin/amylose ratio does not explain all textural issues related to rice, but is a very important factor. Level of Protein. Protein levels in rice range between 5 and 10 percent. The level of protein differs depending of variety, growing area, and crop year. In general, rice protein has a bad taste and so the rice tastes better with less protein. Protein also probably affects the texture of the rice in ways that we do not understand. Cracking and Fissuring of Rice. This is probably the biggest factor affecting the quality of cooked rice and yet is the least understood. The quick migration of moisture through rice causes cracking in kernal. Quick changes in temperature can cause cracking. These can be cracks that are large enough to open up and cause the rice to break during cooking, or that can be small fissures throughout the kernel. The problems with cracking start in the field. If rice is near harvest moisture contents of 20 to 26 percent and starts to dry too fast (due to dry winds, for example), then the rice will develop cracking while in the field. If the rice is dried to fast in commercial dryers, then cracking can occur. Cracking can occur in milling (especially in older frictional mills) where milling temperatures get high. The sudden release of surface moisture or change in temperatures can cause cracking. The pressure applied in milling can cause cracking. When the rice is cooked, open cracks allow moisture to enter the kernel too quick. There is too much surface area where starch is leached out. The kernel does not maintain its grain shape and get mushy. There are some theories that cracking releases enzymes that affect flavor. Moisture. The moisture of the rice prior to cooking also affects texture. If the moisture is below 13%, the quick movement of water will cause cracking. The lower the moisture, the greater the cracking. Once again, rice that cracks will have a poor cooking texture. Age of Rice. This is another area where little is understood. The Japanese believe that good rice is alive, (good rice while in the paddy or brown form will germinate and grow.) and so they prefer to eat rice fresh after milling. Age creates changes in the nature of the starch. Rice gets harder with age as if the percentage of amylose is increasing (it is not). The rice gets firmer and less sticky. Most older rice loses moisture and so the cracking problem during cooking occurs. If there is any bran on the surface of the rice due to loose milling, then the rancidity problem causes poor flavor. Any insect problems while in storage affects odor. Aromatic rice like Thai Jasmine lose their aroma with age. Sticky types of rice like Japonica short and medium grain rice are best consumed immediately after harvest. The texture of parboil rice does not change much with aging. Some harder rice like Indian Basmati are best consumed after several years of aging. But Indian Basmati is an exception, in general aging of rice deteriorates quality. |
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