Rice Flour

Rice Flour

Rice flour does not have any inherent advantages over the use of wheat flour. It is a fairly nutritionally poor white flour, as rice is one of the cereals with the highest starch content. Its protein, fibre, and bioactive substance content are lower compared to other cereal flours. Rice flour also does not contribute any specific aroma or flavour, being quite neutral. Lastly, the cost of rice flour is higher than that of other flours like wheat in Western countries.

Rice flour is primarily used in countries where rice is predominant, more economical than wheat, and there exists a culinary culture associated with it.

Rice is a harder cereal than wheat, and in the milling process, after the grain is dehusked, the bran and germ are removed together through abrasion. In some countries, there are plants that extract and commercialize the oil obtained from this mixture of bran and germ. However, in Spain and most Western countries, such industries do not exist. The high oil content in the mixture of bran and germ, combined with enzymatic content and the method of extraction (friction), causes this mixture to become rancid very quickly. Therefore, to obtain whole grain flour, it is necessary to stabilize this mixture in some way before incorporating it into the white flour obtained from the endosperm. The most common methods of stabilizing this mixture involve thermal treatments, such as extrusion or other means, that deactivate the enzymes (lipases and lipoxygenases) that facilitate rancidity.

Whole white rice grains (without bran or germ) are marketed as is. However, in the process of obtaining rice flour, some grains break and must be separated, as the presence of broken grains is a quality factor in whole rice packages. These broken grains have traditionally been the main raw material for obtaining rice flour, as they constitute a byproduct of rice factories and are more economical than whole grains. Generally, plants that produce rice flours are mills that grind other cereals but do not have facilities to dehusk and remove the bran and germ, so starting from white grains is an added advantage. With the increase in rice flour consumption, especially for gluten-free products, it may sometimes be necessary to resort to purchasing whole grains (without husk or bran), or at least starting from these, due to the lack of broken grains.

Applications of Rice Flour or Semolina

In western countries, rice milling products are mainly used for two purposes. Firstly, a product with a particle size larger than flour (semolina) is obtained, which works very well as a release agent to prevent dough from sticking to certain surfaces. Generally, semolina works better for this purpose than flour. Rice, being a hard grain, is better suited for producing semolina than other softer grains (wheat, rye, or barley), and its neutral flavour does not negatively influence the final product’s quality. This semolina is used in making pizzas and other doughs, as well as in cooking, by sprinkling it on the surfaces where the dough will be worked. Generally, these semolinas do not need to be gluten-free, as they will be incorporated into products made with wheat flour. However, if used for gluten-free products, precautions must be taken to avoid cross-contamination.

The other use of rice flours is their incorporation into formulas for gluten-free products. In these cases, it is essential that rice flours are not contaminated with other gluten-containing cereals, which is difficult to guarantee in mills where wheat or rye are processed. Making bread with rice flour results in products with lower volume compared to those made with cornstarch and with a less cohesive texture compared to those made with potato starch or tapioca, so mixtures with other flours and starches must be tested. However, rice flours are very suitable for making cakes or similar gluten-free products, as well as cookies. In these cases, where gluten formation is not required, they can replace wheat flour in most recipes with minor adjustments.

Milling and Quality of Flours

As mentioned, rice flour is obtained from broken or whole grains from which the bran has been removed. Although various systems can be used, the most common ones are hammer mills or roller mills. Being a harder grain than wheat, obtaining fine flour (less than 180-200 microns) requires more energy and damages a greater amount of starch. Grinding in hammer mills involves continuous friction until particles smaller than the sieve placed exit the mill through that sieve. Grinding with rollers is more progressive, causing less starch damage and allowing the obtainment of fractions with differentiated characteristics.

One of the major issues with rice flours is their lack of consistency. Flour characteristics can be influenced by aspects such as the degree of damaged starch, particle size, or amylose/amylopectin content, which is related to the rice variety used. The fact that their use has been minor, and that these flours have been obtained from broken grains, has led to considerable variation in flour quality. Broken grains are usually not of a specific variety but of mixtures that vary, with grains varying in hardness and amylose content. When rice flours are used in small proportions or for purposes like release agents, these variations may not be a problem. However, when rice flour is the base of a formula, these variations can significantly affect the volume and texture of the products obtained. Therefore, rice flour specifications should include particle size as specifically as possible, and it would be advisable to include water absorption capacity or degree of damaged starch. Particle size is sometimes detailed as the amount that exceeds 200 microns, but below this size, there may be a great deal of diversity, so it should be detailed more precisely. The measure of water absorption is related to both particle size and degree of damaged starch, and greatly influences the preparation of gluten-free bread or cookies.

For making cookies, a larger particle size is usually preferable, although it depends on the formulation. This way, cookies expand more during baking, and the final texture is not as hard. For cakes, a finer size is required, especially for sponge cakes. Coarse flours generate dough with air distributed in larger and less stable bubbles, resulting in reduced final volume. For bread making, coarser flours may result in a sandy texture, but finer ones require a higher water content, due to their greater water absorption capacity, to obtain adequate volume.

Rice Flours in Other Countries

In Southeast Asian countries, there is a greater variety of rice flours due to the cultural significance of this cereal and the greater use of these flours.

Regarding the milling system, in addition to dry milling, there are wet and semi-wet milling methods. The more water the rice has in the milling process, the softer it is and the less starch damage it suffers. However, this moisture must be removed later, with the consequent energy cost.

As for rice varieties, we usually work with long-grain (indica) and medium or short-grain (japonica) varieties. Most long-grain varieties have more amylose content, so their starch tends to retrograde more. This is why these grains remain more separate after cooking. Long-grain varieties also tend to be harder than short-grain varieties, resulting in naturally coarser flours. However, these differences between long and short grains do not always occur, and there are short-grain varieties with high amylose content or harder than some long grains.

In countries like Japan or China, it is also common to work with waxy varieties, which do not contain amylose and therefore do not tend to retrograde. These rice grains tend to stick together after cooking, which is why they are also known as glutinous rice. These varieties are widely used to make certain doughs in Japan and other countries. These doughs are usually cooked in the presence of steam or covered to avoid moisture loss, and the final result has a moister texture. It is known that these flours, by themselves, produce gluten-free breads with very low volume, but they can be interesting in small quantities.

More information:

Bao, J (2019) Rice: Chemistry and Technology. AACCI. St Paul, MN (USA)

Rosell, CM; Gómez, M (2014) Rice. En W. Zhou (Ed) Bakery Products Science and Technology. John Wiley & Sons. Chichester (UK)

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