September 01, 1999
by Teresa Acklin
U.S. millers use a range of treatment options to improve the appearance, baking properties and nutritional content of wheat flour.
By Ian S.V. Trood
It is commonplace in many flour mills around the world to improve the appearance, baking properties and nutritional content of flour during the milling process.
The United States in particular allows and uses a range of flour treatments, including flour bleaching conditioners, flour oxidizing conditioners, enzymes and enrichment. These treatments, combined with access to a variety of high quality wheat, gives the American miller unsurpassed ability and flexibility to provide top-quality flours with unique and improved characteristics.
Flour bleaching conditioners, such as benzoyl peroxide and chlorine, are used to whiten and reduce microbial contamination.
Benzoyl peroxide makes flour, and the resultant bread crumb, whiter in color. The miller also can make the bread crumb whiter by using lipoxygenase enzyme-active legume flour, made typically from soy or fava beans.
A normal treatment rate for benzoyl peroxide is 50 parts per million (ppm) or one quarter ounce per hundredweight of flour of a 32% BPO premix. Bleaching begins immediately and most of the bleaching action is complete within six hours, although trace amounts will continue the whitening process for about two days.
Chlorine also has a whitening effect. A typical chlorine treatment for cake flour is about two ounces per hundredweight or enough chlorine to bring the flour pH down to about 4.8. Chlorine is used on cookie and cracker flours to control batter flow characteristics, spread and the resultant cookie diameter. Flour mills also chlorinate the water used to temper wheat prior to milling as a way of reducing microbial contamination. This typically results in lower mold and bacteria counts. Flours with low microbial counts are beneficial in refrigerated dough.
Chlorine gas is used on cake flours, some cookie flours and some all-purpose household flours. It gives an improved high sugar ratio cake.
Different types of oxidizers have been used in the United States for nearly a century to improve flour. The primary ingredient used today to mature flour is azodicarbonamide.
Prior to the use of artificial maturing, flour was stored for months to allow it to oxidize naturally to provide good bake characteristics. While this may have improved the flour's baking properties, it also increased insect and rodent infestation problems.
At one time flour was always sifted before it was used in order to remove insects from the flour. Today, concerns over insect infestation and the need to reduce the use of pesticides make this an unacceptable option for the industry.
Azodicarbonamide is used at the mill all year long to improve the uniformity of the bread-making properties of flour. It also is considered a bleaching agent within the framework of American regulations.
Flour milled from fresh wheat may require more azodicarbonamide, while wheat that is stored for many months will require less. A typical mill addition rate of 4.5 ppm of azodicarbonamide will minimize the variances. At this level, it is considered a maturing agent and the result is similar to naturally aging the flour.
Higher treatment rates, up to the maximum allowable level of 45 ppm, are used in high ash flours (clears or strong bakers) or to replace potassium bromate. Azodicarbonamide is typically added to flour as a 10% free-flowing premix. An addition rate of two grams per hundredweight of flour is used to give 4.5 ppm.
Azodicarbonamide is a fast oxidizing agent with its action fully completed by the end of mixing. Household consumer flour is rarely treated with azodicarbonamide since it generally sits on the grocery shelf long enough to age naturally.
Ascorbic acid (vitamin C) has become a widely used bread improver worldwide since the demise of potassium bromate. Because of its higher cost and limited effectiveness compared to potassium bromate and azodicarbonamide, ascorbic acid was not used extensively in flour in North America until recently.
Ascorbic acid addition rates in flour typically range from 25 to 75 ppm. The maximum level is 200 ppm; levels in excess of that are of no additional benefit.
Millers typically use diluted premixes of ascorbic acid that have been blended to make addition more consistent. Ascorbic acid tends to give a tighter, finer grain than azodicarbonamide or potassium bromate, but generally is not as effective in improving loaf volume.
Ascorbic acid and azodicarbonamide work quite well together when added to flour, a practice that has become quite common as a replacement for bromate. The high temperatures used in baking destroy the vitamin C value of the ascorbic acid, which prevents bakers or millers from making a nutrient claim for vitamin C.
Potassium bromate, one of the oldest and most effective oxidizing improvers for bread flour, is still widely used in the mills in the United States, except California (see story on Page 20). It improves the volume and the structure of many bread products while imparting a tolerance to dough abuse that is unrivaled by other ingredients.
One potassium bromate premix has been diluted with inert salts to reduce the risk of combustion and explosion, which is possible when handling concentrated potassium bromate. Treatment rates for bromate range from 15 ppm for a typical patent bread flour to 50 ppm for very short (no time) or very long (overnight) fermentation methods.
Potassium bromate is considered a slow-acting oxidizer with its effect extending through the entire baking process. Only after full baking is all the bromate destroyed. Some studies have suggested that in certain conditions residual bromate can remain in the bread even after baking. Mill and bakery employees should exercise care to ensure contact with potassium bromate is minimized.
Enzyme supplements are added to enhance flour fermentation. Millers can add either malted barley flour or fungal alpha amylase enzyme to supplement the natural diastatic activity of wheat flour.
In America, malted barley flour addition is still the norm. However, millers and bakers outside the United States have found that amylase gives more predictable results with reduced infestation concerns. There is a definite trend in the U.S. toward increased use of amylase derived from the mold aspergillus oryzae.
Typical amylase products for use in mills are standardized at 2,500 or 5,000 skb units per gram with controlled protease levels. Protease levels can be either very low or similar to that provided by malt addition, depending on the dough handling characteristics required.
A normal addition of these amylase products range from two to four grams per hundredweight of flour. Increased levels of fungal amylase are often used in combination with ascorbic acid or azodicarbonamide to replace potassium bromate.
Flour enrichment has been an important part of improved public health in the United States and many other countries around the world. Diseases caused by vitamin deficiencies were widespread earlier this century. The implementation of vitamin enrichment has played a major role in making the occurrence of diseases such as beriberi and pellagra very uncommon in North America.
In the U.S., flour is enriched with iron and four B vitamins — thiamin, riboflavin, niacin and folic acid. Enrichment of flour and bread is not required by U.S. federal regulations but most states have mandatory enrichment regulations.
It is estimated that at least 95% of bread sold in the United States is enriched. Enrichment may be applied at either the bakery or the mill, but economics heavily favor addition at the mill.
A typical cost of enriching flour with the four B vitamins and iron is about U.S.6 cents per 100 pounds of flour. The average per capita consumption of flour products in America is around 150 pounds per year. This means it costs, on average, less than 10 cents per person per year to provide the benefits of enrichment to all Americans through flour fortification.
Thiamin (vitamin B1) is required to help the body use its major source of energy, carbohydrates, to the fullest extent. Thiamin also is essential for proper muscle coordination and the maintenance of peripheral nerve tissue. Thiamin deficiencies can lead to beriberi, a disease characterized by inflammatory or degenerative changes to the nervous system, digestive system and heart.
Riboflavin (vitamin B2) helps the body transform proteins, fats and carbohydrates into energy. It also helps the body maintain healthy skin and eyes, and is necessary for building and maintaining body tissues.
Niacin (a B complex vitamin) is essential for fat synthesis, protein metabolism and the conversion of food energy. Niacin has been a factor in preventing pellagra, a condition characterized by reddish rashes that later turn dark and rough. Pellagra became widespread in North America about 1907 and killed approximately 10,000 people in 1915 alone.
Folic acid plays a major role in the prevention of neural tube birth defects such as spina bifida. It has been shown that the addition of folic acid to the diet of child-bearing women before conception can lead to a reduction of the incidence of spina bifida by as much as 50%. This evidence has lead to its inclusion in flour in the U.S. and many other countries.
Iron is essential for cell maturation, protein formulation and as a carrier of oxygen throughout the blood stream. Infants and women have the highest probability for iron deficiency.
Iron is available in many forms. The two forms most commonly used in flour and semolina in the United States are reduced iron and ferrous sulfate.
Reduced iron is the most often used source of iron. It is magnetic and has only fair bio-availability, but is very stable and will not promote rancidity.
Ferrous sulfate often is used as an alternative to reduced iron when a non- magnetic form is required, and has excellent bio-availability. The principal drawback to ferrous sulfate is its tendency to promote rancidity during storage in the presence of fats. For this reason, ferrous sulfate is not suitable for the treatment of industrial mixes or household consumer flour, but is well suited for industrial flour and semolina destined for pasta production.
Ian S.V. Trood is general manager of the flour service division of American Ingredients Company, Kansas City, Missouri, U.S. He can be reached at firstname.lastname@example.org.