Criteria for Judging Quality
A very simple way to determine color differences in different batches of flour is to look at the color of different types of flour under a sheet of glass. This can be done with more than one flour at a time. This method not only facilitates a comparison of the whiteness of different flours but allows for an inspection for impurities. The flour should have a..." perfectly regular consistency and not contain any specks" (2). This obviously does not pertain to mixed grain or to other than white flours.
Texture and Feel
The texture and size of the grains play an important role in kneading and also determine the speed at which the dough rises(3). In general, bread flour is slightly coarse and falls apart when pressed into a lump. Pastry flour is smooth and fine and can be squeezed into a lump. Cake flour is smooth and fine, can be squeezed into a lump, and stays in a lump more solidly when pressed.
Expansion and Extensibility
Several factors determine the rising ability and elasticity of a particular flour. In France, Italy and the US the Chopin Alveograph, or Extensopraph is used to determine the relationship between the elasticity of the dough and rising power. An example of an Alveograph reading on a number of dough samples is presented below.
Putting a sample of dough to the Alveograph test allows one to measures the resistance of the dough to expansion and the extensibility of a thin sheet of the dough. "P" expresses the resistance of the dough to deformation, and is related to the dough's tensile strength and stability (2). It is measured in millimeters (mm) and then multiplied by the factor 1.1. Flours with a high "P" value tend to have a high gluten content and absorb a relatively large quantity of water. The letter "L" measures the distance , in millimeters, from the start of the curve to the point where the dough bubble ruptures under the conditions of this test. "L" represents the extensibility of the dough or its ability to rise.
Measuring the area under the curve and then multiplying it by another factor (6.54) affords the value of "W". "W" is proportional to the baking strength of the dough. Values of "W" range from 45 for very soft flours to 400 for very strong, hard red wheat flours. The relationship between "P" and "L" expressed as a ratio serves as an index of gluten behavior. High values of "P" and "W" indicate a strong flour.
The following information (Table IX) is adapted from the Molina SIMA (8) recipe booklet, and represent the range of values for "W" as applied to Italian wheat flour and breads.
<120 Poor quality flours, unusable for bread making 120 - 160 Weak flours, appropriate for the production of Biscotti 160 - 250 Medium or average strength flours, used for soft doughs (paste molli) in the production of Pugliese, ciabatta, Francese, pane piuma, etc., for firm doughs (paste dure) in the production of pane ferrarese , and also for the refreshment of natural yeast (lievito naturale). 250 - 310 Flours of strength obtained from high quality national wheat and strong wheat of national or foreign origin, used in the production of maggiolino, baguette, rosetta, soffiato, & biove. 310 - 320 Flours extracted from strong wheat, used primarily for doughs with a long fermentation, indirect method doughs employing a biga or lieviti (natural yeasts) with long rises, or for sweet raised doughs such as pandoro, panettone, veneziane, etc.
Capello (5), providing another view, states that if the formula or recipe calls for a long rise (indirect method, biga), a flour able to tolerate long rises and more work time (i.e. "W" of about 260-300) should be utilized. By comparison, if the formula calls for a shorter rise (direct method) it is appropriate to use a flour with a lower "W" lower (i.e. "W" of about 200-230 or lower). otherwise, the use of a stronger flour may damage the resulting product.
The following information is also adapted from the Molina SIMA (8) recipe booklet, and describes the "P/L" ratio which serves as an index to the behavior of the gluten.
The P/L expresses the relationship between the tenacity and extensibility of the dough, connoting a value of equilibrium or unbalance between these two factors. The equilibrium is expressed (according to the type of production and technique employed) between 0.40 and 0.70. These values indicate that, in relationship to the "W", a baker will be able to produce a bread with maximum volume and a well proportioned inside structure. While this may sound esoteric, it is not.
When The Artisan receives recipes from baker colleagues in Italy, the "W" value of the flour used is also provided. Since we do not have equivalent information about American flours, we test bake until the process produces a bread similar to that described in the recipe. Our task would be much easier if we had access to the "W" values of our American flour. An example of an Italian recipe using the "W" values in the recipe (formula) may be seen in the recipe for a Croccantina (Ciabatta) provided by our colleague Sergio Agosti of Il Fornaio in Salo, Italy.
Higher P/L values indicate flours that are more difficult to work and that result in a bread less developed with a compact crumb. Lower P/L values indicate flours that will be weak, too extensible, and difficult to work because they are often sticky. The bread which results will be flattened because the dough has not succeeded in holding back the developing gases. The indices most often used for appraising the plastic qualities of the flour are the "W" and the "P/L".
The "W" is utilized in conjunction with information obtained from the data afforded by measuring mixing resistance of dough on an instrument called a Brabender Farinograph and results in a Farinogram. The information presented below, including the Farinogram (Chart 2), is from Pyler (3) The Farinograph uses the resistance of the dough against the kneading arm during the mixing process as its means of measurement. The purpose of this test is to determine the amount of water the dough can absorb as this indicates the dough's firmness and dough yield. Additionally the Farinograph determines the degree of softening of the dough when mixed for too long. This provides information about the doughs stability. Specifically, Farinograph tests determine the following:
- Water absorption is indicated as the amount of water needed to develop a standard dough of 500 Brabender Units (BU) at the peak of the curve. In the case shown on the graph Absorption is 60.7% The absorption rate is the quantity of water, expressed in percentage, that is required to give a sample of dough a fixed consistency.
- The Peak Time is the time needed for the curve to reach the peak or maximum dough consistency, and indicates the relative strength of the flour.
- The Arrival Time is the time required for the top of curve to first intersect the 500 BU consistency line.
The Departure Time is the time required for the tip of the curve to drop below the 500 BU.
the interval between the Arrival and Departure Times (see abive definitions). It is often referred to as the tolerance of the flour to "over" or "under' mixing. Chart 2 below includes Stability times. Chart 2
- The Mixing Tolerance Index (MTI) is represented by the difference between the Peak Time and the Departure Time, and is a measurement used to indicate the mixing requirements of the flour. Stability Time -- the horizontal line directly under the Peak Time -- is 11.0 minutes in this sample, and represents
- The Stability of the dough is the interval of time that it remains at maximum consistency, and is very important relative to the type of fermentation and mechanical stress to which a dough can be subjected. The Stability Time (S) or mixing tolerance is an important index of flour quality.
All dough eventually break down on sustained mixing. Excellent quality flour breaks down at between 0 and 30 Brabender Units and has a Stability Time, expressed as "S" of greater than 10 minutes. Poor quality flours breakdown between 70 and 130 BU's and have a Stability time of not less than 3 minutes. It has been noted (8) that a strong flour with a "W" > 250 and an "S" > 10 will tolerate long processes of varying times, while a weak flour will not. Table X compares Brabender Units and stability factors for a variety of flour qualities (9).
Table XAll of these data are used at the mills to determine the quality of the flours produced. We have discovered only one mill which provides these data. That is Cooks Natural Products. Log onto their Internet site and see how they present their wheat and flour information. It includes, Alveograph and Farinograph data, the Falling Number, Ash content and a lot more!
Excellent Quality Breakdown of dough between 0 and 30 BU: S>10 minutes Good quality Breakdown of dough between 30 and 50 BU: S not less than 7 minutes Fair quality Breakdown of dough between 50 and 70 BU: S>not less than 5 minutes Poor quality Breakdown of dough between 70 and 130 BU: S>not less than 3 minutes Inferior quality Breakdown higher than 130 BU
Fermenting Ability and Enzyme Content
The quantity of enzymes (amylases) contained in flour determines the rate at which starch is converted to sugar and thus rendered accessible to the yeasts. Alpha-amylase is the specific enzyme measured in this test relative to its ability to liquify starch. Too high an amylase content results in high fermentation sugar values in the dough, whereas too low an amylase content results in a dough with little gassing power(2). The alpha amylase activity and its relationships to the bread baking process are measured by "The Falling Number". Another amylase, Beta-amylase is also involved in the breakdown of starch into sugars, especially maltose. Readers interested in an exhausive discussion of enzymes and baking are referred to both volumes of Pyler (3)
The Falling Number (or Hagberg Index) is indicative of the amylase (specifically alpha-amylase) activity and the fermentation process taking place in a wheat flour dough. It is based on the rapid gelatinization of flour suspended in water and measures the degradation of starch made available from alpha-amylase activity in rising temperature conditions similar to those of bread making.
The following Falling Number values are inversely proportional to the amylase activity. The information provided below (Table XI) is meant as a guide. Contact your flour mill to ascertain specific numbers for the flour you use.
Elevated amylase activity. This flour is derived from germinated grain, and its use results in a bread crumb that remains sticky and under baked. It is nearly unusable unless it is adequately mixed with other flour with a higher Falling Number.
150 - 220
Superior amylase activity to that which is normal. This flour requires a correction by being blended with flours of a higher Falling Number or using particular bread making methods during production.
220 - 280
Normal amylase activity.
>280 - 300
Weak amylase activity. The use of this flour results in bread that is not well developed, with low volume and too dry a crumb. It requires the addition of diastatic malt.
If the moisture content of a flour is elevated, the flour will have a shorter shelf life and lower yield. A guide to water content and flour relative to storability is as follows: A water content greater than 16% cannot be stored. A water content of about 15% has limited storage potential. A water content of less than 15% indicates good storage potential (6).
Absorption measures the amount of water that can be absorbed by a given quantity of flour. In bread making, it is usually preferable to have flour that can absorb a large amount of water. Measurements of absorption are done to determine the amount of water the dough can absorb, which in turn indicates dough yield and shelf life. Optimum absorption represents the maximum amount of water, as a percent of the flour weight, that will produce a high yield of bread during the baking process (1). Other tests exist which measure a flour's ability to absorb water, but we shall not discuss them here. They are beyond the scope of this presentation, but may be found by examining the references provided.
The Maltose Number relates directly to the gassing power of the flour. Stronger flours have higher gassing power.
A graphic display of some of the information presented above is contained in Table XII below, which was excerpted from Baking, The Art and Science (6).
Weak flour for biscuits,sponge cakes and tart doughs Standard-type flour for white bread, wheat/rye bread and rolls Strong or high protein flour for white bread, French bread and soft rolls. RMT-Volume Yield 400 - 670 620 - 730 710 - 760 Protein Content 8 - 11.75 11.2 - 13.5 12.7 - 14 Maltose Number 1 - 2 2 - 3 2 - 3.5 Fall Number 200 - 300
Note: The Volume Yield is done by the RMT = Rapid Mix Test, a Standard Baking test for bread