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Evaluation of flour quality for steamed bread processing – a model using Canadian wheat

B.X. Fu, E.G. Assefaw, and G.R. Carson

Canadian International Grains Institute (CIGI), 1000-303 Main Street, Winnipeg, Manitoba, Canada R3C 3G7


Steamed bread is a major flour product consumed in Asia-Pacific countries. Varieties of steamed bread differ among regions and countries. There are basically two classes of steamed breads based on their formulations. One contains essential ingredients only (flour, water, and yeast or sourdough starter) and is called ‘lean-formula steamed bread’. The second class also includes up to 25 percent sugar and 10 percent shortening and other optional ingredients and is referred to as ‘rich-formula steamed bread’. The key differences between steamed bread and baked bread are water absorption for dough mixing, method of cooking, and way of serving. Steamed bread doughs are stiffer and much less ‘plastic’ than baked bread dough. With steamed bread, steaming is usually carried out at atmospheric pressure and, thus, the cooking temperature is much lower than that for baking. Due to the low temperature of the steaming process, hardly any flavour compounds are produced during cooking and only a very thin and soft skin is formed. The flavours of steamed bread mainly result from the fermentation process. With baked breads, the brown crust formed by maillard reactions during baking, is the major source of bread flavours. Steamed bread is usually served when it is warm and can be refreshed by re-steaming. The white thin skin of steamed bread, however, is susceptible to many defects.

The desired steamed bread characteristics depend on the style of the product and regional preference. Some quality attributes, however, seem to be widely accepted. In general, steamed bread should have a smooth, bright white surface and a symmetrical shape. Undesirable external defects include wrinkles, blisters, dimples, gelation spots, a yellow or dark coloured skin, and a flat or poor symmetrical shape. Steamed bread should have a white and uniform internal crumb that is elastic and does not stick to the teeth during chewing. The texture varies from very firm for some lean-formula breads to soft for rich-formula breads.

The flour quality requirements for steamed bread processing depend on bread type, with formulations and processing conditions having significant impact. Appropriate evaluation of wheat and flour quality is of importance for wheat exporters, breeders, millers, and steamed bread processors. High quality wheat or flour is expected to perform well in a wide range of formulations and processing conditions. This paper outlines the procedures and protocols for laboratory steamed bread processing and quality evaluation. Guidelines described are designed to ensure the test methods demonstrate the flour quality potential for steamed bread production and processing tolerance, but not optimized quality. Results of our research on steamed bread processing tolerance and surface gelation are also discussed.

Materials and methods

Wheat Samples

Samples of top grade Canada Western Red Spring (CWRS) and Canada Western Hard White Spring (CWHWS) wheat from 2003 crop were milled separately using a Buhler pilot mill at CIGI. By combining selected mill streams, 72% extraction patent flours were obtained. The flours were analyzed for protein and ash contents and characterized by Amylograph and Farinograph (Table 1).

Table 1. Flour Used for Steamed Bread Evaluation


Protein (%)

Ash (%)

Amylograph Peak Viscosity (B.U.)

Water absorption (%)

Development time

Stability (min)















Procedure for Making Steamed Bread

Flour (600 g), water (variable), yeast solution (15 g fresh yeast dissolved in 100 g of water at 36oC), and for rich formula only, sugar (72 g) and shortening (24 g) were mixed in the GRL-1000 mixer for 30 sec at 45 rpm, then the dough was developed at 105 rpm for the required time. After 10 min of resting, the dough was sheeted by passing through a 5.5 mm gapped sheeter 16 times. The dough sheet was subsequently rolled into a cylinder. Five or six dough pieces (150 g each) were sampled and then rounded by hand. The dough balls were placed in a steamer tray, proofed for 30 min (lean formula) or 45 min (rich formula) at 32oC and 85% RH. Proofed dough balls were steamed for 25 min in a commercial aluminum steamer.

Steamed Bread Evaluation

Steamed breads were allowed to cool for 30 min, and then weighed. Volumes were determined by rapeseed displacement. The width and height of each bread were measured at three different locations, and the average recorded. The colour of the steamed bread skin and crumb were measured by a Minolta Chroma Meter CR-310 equipped with a C illuminant using the L*, a*, and b* colour scale. Breads used for sensory scoring were re-steamed for 10 min, and allowed to cool for 15 min before evaluation. Breads were scored by a trained sensory panel using the scoring system provided in Table 2.

Table 2. Sensory Scoring System for Steamed Bread

Quality parameter




Exterior appearance





Round and symmetrical shape



Smooth skin, free of wrinkles, dimples, blisters, and gelation spots

Skin colour


Bright white


Crumb structure and colour



Crumb colour


Bright white

Crumb structure


Uniform and fine crumb


Crumb texture





Force required to deform and break crumb



Recovery after compression with molar teeth



Low degree of stickiness to the teeth during biting

Total Score



Experiments Conducted

Preliminary tests were conducted to determine the water absorptions and mixing times of the flours for both lean and rich formula steamed breads. The flours were then evaluated for steamed bread quality under fixed formulation and processing conditions. Processing tolerance, as measured by tests varying in water absorption and mixing time, was also examined for the two flours. Surface gelation, a common and troublesome product failure in steamed bread production, was investigated by the addition of monoglycerides in the formulation.

Results and discussion

Quality of CWRS and CWHWS for Steamed Bread Processing

CWRS and CWHWS produce high quality steamed breads using both lean (Fig.1) and rich (Fig.2) formulations, as indicated by the round and symmetrical shape, smooth and bright white skin, and uniform and fine crumb structure.

Processing Tolerance of Steamed Breads

There is a huge variation in formulation and processing conditions for steamed bread production in Asia. It is difficult to discuss wheat quality requirements for steamed bread applications without taking the formulation and processing into consideration. Water absorption, mixing time, the amounts of shortening and sugar added could greatly affect the final product quality. At fixed mixing times of 10 min for lean formulation and 7 min for rich formulation, an increase in water absorption from 40% to 43% resulted in the collapse of the steamed bread produced with lean formulation (Fig. 3). On the other hand, there was no significant effect from a similar increase in water absorption on rich formulation steamed bread (Fig. 4).

Bread of lean formulation was also more sensitive to mixing time than rich formulation. At a fixed water absorption of 40% for lean formulation and 42% for rich formulation, a decrease of mixing time from 10 min to 6 min resulted in the collapse of the lean formulation bread (Fig. 5). The effect of mixing time on rich formulation bread was not significant (Data not shown) (Fig. 6). These results indicate the rich formulation has a higher processing tolerance than the lean formulation.

Surface Gelation of Steamed Bread

Surface gelation is a common and troublesome product failure at both commercial production and laboratory testing levels, especially for steamed breads produced with lean formulations. The effect ranged from minor ‘burned skin’ to full gelation (Fig. 7). The phenomenon of surface gelation appears to be related to flour properties and processing, and is very random. It occurs mostly at the moment cold air mixes with hot steam, and always starts at the bread surface. There was no published information related to the mechanism of surface gelation. The return to crystallinity could be the process responsible for the gelation after steam cooking and immediate cooling when the steamer is opened. Amylose forms opaque, partially crystalline, thermo-irreversible gels. Based on this hypothesis, additives which can prevent the crystallization of amylose should be able to reduce or eliminate bread surface gelation. This theory was confirmed by the fact that incorporation of 0.5% monoglycerides (MG) into steamed bread formulations can essentially prevent gelation on the steamed bread surface (Fig. 8).


Guidelines and methods have been established for laboratory steamed bread processing and quality evaluation. Rich formulations have a higher processing tolerance than lean formulations in the production of steamed bread. Hard wheat, like CWRS and CWHWS, is not only good for breads of lean formulations but is also well suited for breads of rich formulations. Monoglycerides are effective in preventing the gelation of steamed breads, thus avoiding ‘burned skin’ and collapse.


The authors would like to thank the CIGI Milling Group for milling of the wheat samples, Analytical Services for analysis of the flours, and Corporate Resources for editing the paper.

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