March 01, 1994
by Teresa Acklin
A discussion of the functional treatments and nutritional supplements that can be added to flour at the mill.
Flour treatments are many and varied, both within and among different countries. In many countries, laws regulate what treatments are allowed and often specify the permissible levels. A check with the correct government authority should be made to determine the status of a particular treatment.
For the purposes of this article, the definition of flour treatment is any treatment given to a flour before it leaves the mill gate. Thus, it excludes treatments used by a baker.
The more common flour treatments can be categorized into those that are functional, which affect flour performance; nutritional, which add health and nutritional supplements; and physical.
Benzoyl peroxide. Freshly milled flour is yellow and will whiten or bleach naturally over some weeks, but in some markets the demand is for bleaching quickly. Benzoyl peroxide in diluted powder form is used for bleaching or whitening the flour pigments, which consist of the naturally occurring substance xanthophyl.
The strength of the additive is often around 16% purity. The remainder consists of a food-grade filler, and thus, the additive is considered a premix.
The amount added should be no more than 35 to 40 parts per million, calculated in its pure form. This is the level that generally is considered most effective; the law of diminishing returns sets in at higher levels, and money is wasted.
The miller can use a wetted Pekar slab, comparing treated with untreated flour, as a quick qualitative test for bleaching. A long quantitative method exists, but it is seldom used in the mill laboratory.
Potassium bromate. Now largely disused because of its potential health hazards, this oxidative improver is very effective, either on its own or with ascorbic acid. Bromate comes in a powder, suitably diluted; typical treatment levels are up to 25 ppm in its purest form.
The function is to produce a larger volume bread loaf, probably by suppressing proteolytic enzymes in flour. A further benefit is to mask inconsistencies in flour.
For the miller, a quick test for presence and dispersion is to use a Pekar slab wetted with equal parts of diluted hydrochloric acid and 1% potassium iodide solution against a known sample. The result is the appearance of brown/black spots. Lengthy qualitative tests exist in specialist laboratories.
Ascorbic acid. This powder, vitamin C, is another slow-acting improver with functional properties similar to bromate. It is in very common use, especially since the demise of potassium bromate.
Because vitamin C is found naturally in many foods, particularly fruits, it is not under any real health suspicion. It is used at up to 50 ppm in pure form for satisfactory bread-making, especially in mechanically developed dough processes.
Ascorbic acid also is used at lower levels in conjunction with other faster-acting improvers, such as the oxidant azodicarbonamide. A useful, quick test is available to millers for the presence of ascorbic acid; as with other treatments, a slower quantitative test also is available.
L-Cysteine hydrochloride. Cysteine is a reducing agent sometimes used in the baking process, less often added to flour. Its effect is to allow quicker dough ripening (relaxing). It is also used in biscuit and cookie production.
Effective levels for bread typically are about 35 ppm and for biscuits, up to 200 ppm. Biscuits, of course, require a certain consistent flowability in the dough made from extensible flours.
Sulphur dioxide. This treatment is added to biscuit or cookie flours by steaming to make flours more extensible.
A level of 50 ppm is often quite enough. Sulphur dioxide is very effective; some say it is too effective because the window of treatment can be missed by excessive degrees.
The majority of biscuit manufacturers do not allow this treatment because the effect wears off rapidly and its presence is difficult to detect.
Sodium metabisulphite. This treatment is similar in function to sulphur dioxide. Many cookie manufacturers prefer to add the treatment in their plant for control reasons and insist that millers do not add it to flour. Sodium metabisulphite is a powder, and a common treatment rate is 0.02% on flour weight.
Proteinase. This enzyme in powder form works in a similar way to sulphur dioxide and sodium metabisulphite in relaxing biscuit doughs. There seldom are any legal restrictions on its use.
Azodicarbonamide. This fast-acting powder oxidant for bread-making is popular. Commonly called ADA, it often is used in conjunction with other bread improvers at rates of around 15 to 20 ppm. The maximum permitted rate is typically 45 ppm.
Because of its speed, ADA shortens classical bread fermentation processes to something closer to mechanical developed dough processes, sometimes called “no-time” dough processes. It therefore eases the baker's daily program, possibly with a certain loss of resulting flavor.
Chlorine dioxide. This treatment is added in gas form generated at the mill. The function is to improve flour for bread by modifying or tightening extensible flours as measured on the Farinograph, Extensograph or Alveograph.
Patent, straight grade or clear flours all require different treatment levels, in order from the lower to the higher; average treatment levels are around 2 grams per 100 kg of flour. Chlorine dioxide has a simultaneous bleaching effect, but the effect is relatively small compared with that of benzoyl peroxide.
The quick test for its presence is to wet the treated and untreated flours side by side on a Pekar slab. Lengthy quantitative procedures also are available.
Use of this treatment is diminishing mainly because the miller must have complicated and sensitive gas generating equipment in the plant. If the gas leaks, unpleasant and potentially dangerous chlorine gas is emitted, necessitating specialist mainentance.
Chlorine. Added in gas form at the mill, this treatment is used for cake flours, particularly so-called high-ratio cakes. High-ratio cakes are defined broadly as those requiring 100 to 120 parts of combined sugar and fat to 100 parts flour.
Made from soft wheat, these flours should be low ash, good color and fine. Chlorine treatment of about 1,000 ppm has the effect of an even-textured, good-volume and light-eating cake. A pH meter in the mill lab will give an indication of correct treatment.
Fungal alpha amylase. This powdered enzyme, prepared from molds, is used to increase diastatic activity in bread and is used instead of diastatic malt flour (cereal alpha amylase). It is safer than malt flour because fungal alpha amylase is deactivated in the oven; its reaction stops at a lower temperature than malt flour, reducing the possibility of an overreaction that could lower quality.
At high treatment levels, fungal alpha amylase properties increase gas retention in doughs, thus allowing a low protein flour to perform as if it were higher protein. Treatment levels depend on the strength of the fungal material, usually measured in so-called SKB units, and the strength needs to be known before use. Laboratory baking tests will give the correct indication of necessary treatment levels in comparison to a suitable control.
Acid calcium phosphate and sodium bicarbonate. Acid calcium phosphate, commonly known as ACP, and sodium bicarbonate are used together in balance to make self-rising flour. Other effective acid compounds also are available. Both acid and alkaline ingredients come in powdered form, and ACP is commonly found at 80% strength.
When water is added to self-rising flour, the action is to produce gas to make aerated baked goods. For both proper carbon dioxide generation and flavor reasons, it is important to use the correct ACP- sodium bicarbonate proportion and to confirm the correct proportion with the laboratory.
A typical formula for 80% strength ACP to 100 parts of flour would be 1.54% ACP and 1.16% sodium bicarbonate. Because the flour gradually loses its gas-generating power over time, this formula provides enough carbon dioxide production after storage. It also assures the taste of the baked goods will be neither too acidic nor soapy, a symptom of excess sodium bicarbonate.
Quick test procedures include a fast baked-goods check, as well as a Pekar slab with a few drops of suitable indicators to highlight the presence and dispersion of the two ingredients.
Other functional additives. Included under this heading are additives of various flavors and colorings, gums, salt, emulsifiers, fats and sugars. Each typically began as a marketing concept and was developed in the laboratory as a premix. Among several factors to consider is the need to design relevant and adequate test procedures to measure the produced material against the design standard.
Lecithin. This substance is used in some countries to give bread doughs a more silky feel and a softer resultant bread crumb. It typically comes from the soybean, and in fact is a mixture of lecithin and cephalin. It is added at a rate of about 0.17% by flour weight.
Bean flour. This additive is widely used, particularly in France for bread. With properties similar to soy flour and lecithin, its effect is to improve the texture, color and softness of the crumb. Typical levels are 2% by flour weight.
With all of these treatments, it is a good idea to check their legality and any maximum treatment levels. It also is important to communicate with flour end users to ensure that functional treatments or additives are neither overlooked nor duplicated. Dough conditioner manufacturers also are involved, and three-way communications often are necessary.
Included in this general category are folic acid, iron, thiamin (vitamin B-1), nicotinic acid (niacin) and calcium carbonate. These substances are added in some countries by decree or law as a health or nutritional supplement.
Folic acid. Much publicity in recent years has been given to this vitamin as a fortification or enrichment to white flour, bread and/or breakfast cereals. The principal benefit is to help pregnant women reduce the risk of giving birth to children with spina bifida or similar neural tube defects.
Some medical experts do not recommend blanket fortification or supplementation; they fear that indiscriminate fortification could pose hazards to other segments of the public, such as the elderly or those with B-12 deficiency, on whom folic acid's effects are not well enough known. In contrast, the U.S. is implementing regulations to require the addition of folic acid in many grain-based foods, including enriched flour, bread, corn grits and meal, rice and noodle products.
When added to flour, folic acid requires suitable labeling. In a pure state, treatment levels would be 140 mcg per 100 grams of flour. Folic acid comes in a powder form and requires a carrier for dilution to ensure safety and accuracy.
As yet, no quick test exists for millers to determine presence and dispersion, although high pressure liquid chromatography is one reliable, if expensive, test.
Iron. Iron comes in a number of different forms, such as fine powder, ferrous sulphate or ferric ammonium citrate. Iron is added to flour to guard against the onset of health problems from anemia. As a powder, the treatment level is 1.65 mg per 100 kg flour.
Thiamin (vitamin B1), nicotinic acid and calcium carbonate. These substances, along with other vitamins, are added to flour to help human growth and health. All three come in powdered form.
Thiamin is added at 0.24 mg per 100 kg flour and nicotinic acid at 1.6 mg per 100 grams. Calcium carbonate, which also promotes healthy bones, is added at 0.3% on flour weight.
There are three principal methods of physical flour treatment: heating, drying and adding moisture.
Heating. This technique, normally accomplished by steam, is used to denature flour for soup manufacture and is used in the paper and corrugating industries for sizing and gluing. The aim is the destruction of alpha amylase activity, which also denatures gluten.
The testing method usually consists of comparing treated to untreated flour samples using the Amylograph. The degree of denaturation can be determined by adding silver nitrate (a poison) to the untreated sample, which kills alpha amylase activity completely. This sample then is compared with the treated sample.
Another technique is to modify rather than destroy or denature. Modification, mainly of the gluten, reduces flour extensibility for baking. The technique is notoriously difficult to control industrially, although it can and has been done.
Testing is carried out by comparing untreated and treated flours on dough rheology equipment such as the Farinograph, the Extensograph or Alveograph.
Drying and moisture addition. Drying is a common treatment that can be carried out on flours destined for sealed packaging, where spoilage, for example, might be a problem. Tests are done through classical moisture-testing methods.
Most flours realistically cannot be dried below 4%. Moreover, if specifications call for gluten vitality to be maintained, which is usually the case, a dough rheology test is carried out to assure the specifications are met.
Moisture sometimes is added to increase the moisture content of flours. This is a financially worthwhile treatment that is tested by the normal moisture determination methods.
All in all, the need for care in the treatment of flours is well known, and care is very necessary. It is one thing to treat, quite another and vital to check by testing that all is in order.
Many treatments exist in addition to those described, and each country has different laws. Reference to relevant government agencies will confirm the legality of specific treatments, as well as treatment levels and labeling requirements.
By David Sugden, a consultant to the grain industry.