TESTING OF NEW-ZEALAND-GROWN WHEATS.

New Zealand Journal of Agriculture, Volume XXVII, Issue 3, 20 September 1923, Page 167

TESTING OF NEW-ZEALAND-GROWN WHEATS.

III. BAKING-TESTS OF FLOURS.

L. D. FOSTER,

Analyst, Chemistry Section, Wellington.

Practical tests being always the more convincing, it was considered advisable, in continuation of the testing of New-Zealand-grown wheats, to corroborate by actual baking-tests information obtained from the chemical examination of flours,. and to illustrate if possible the truth of the statement that the protein content of a wheat (or flour) is generally a fair measure of its strength. Baking-tests of the flours from wheats, which were experimentally milled have now been successfully carried out in this Laboratory. For the results of the chemical analyses the reader is referred to Table II in this series, in the August issue of the. Journal.

Bread, according to T. B. Wood, is the product of cooking or baking a mixture of flour, water, and salt, which is made porous by the addition of yeast. Several varieties of the process of breadmaking are practised, but for the purposes of these tests, the “ straight-dough ” process was used, and for the following reasons : It required less time, it was easier to control the temperature-changes over a comparatively short period than over the longer periods of the other methods, and the results were likely to be more accurate. - . - •

It is at once apparent that in making tests on . different samples it is imperative that they should be so conducted that the differences in results are due to the inherent qualities of the flours themselves, and not to modifications of the method used. It is therefore of importance that the conditions under which the tests are carried out should be strictly the same in every case. These conditions are maintained chiefly by careful regulation of the temperatures from the time the dough is first mixed to the time the bread is finally removed from the oven. 1

METHODS OF BAKING (STRAIGHT-DOUGH PROCESS).

In order to maintain the necessary temperature conditions the different ingredients were warmed to 35 0 C. before being incorporated in the dough;. this was thoroughly mixed and kneaded, weighed, and allowed to ferment for a specified length of time in a fermentationchamber kept also exactly at 35 0 C. Here the dough was allowed to rise to a maximum height, when the'amount of rise and the. time taken were noted, and the dough again weighed... It was then immediately put into the oven, which was kept at 220° C. ; the loaf was baked at that temperature for thirty-five minutes. With each series of loaves—only six of which could be baked at a time- commercial “ baker’s ” flour was included for purposes of comparison and for standardization of the various series.* On being taken from the oven each loaf was removed at once from its tin, weighed," and cooled as quickly as possible. After standing for one hour the volume of each loaf was measured. To produce bread of good quality from the point of view of size, uniformity of texture, &c., the dough (in other words, the gluten) must be —that is, it must expand or “rise.” The volume of a loaf is a measure of this elasticity, and, it follows, of its quality. Having baked the loaf and measured its volume, other things (colour, &c.) being equal, a practical measure of quality or strength is obtained.

In each case exactly the same amounts of each ingredient were used for the tests, and each dough received exactly the same treatment, except that (a) the amount of water added was suited to the requirements of the flour as shown by the absorption-of-water figure, and (&) the fermentation period was varied to allow a maximum expansion to be reached in each case ; in the case of weaker flours this period was generally longer than with stronger samples.

BAKING-TESTS.

It will be remembered that in the second article of this series it was said that the amount of protein present was probably, the best single measure of the strength of a flour. A series of loaves containing high to low amounts of protein, and illustrating this statement, is shown in Fig. 1. It is at once apparent that here No. 2 is easily the best as regards volume, and that the value of the others is in descending order of protein content. No. 1 is from the commercial flour baked with each series. ■ The largest loaf is from a sample of Velvet grown at Middlemarch, Upper Taieri, on the borders of the arid district of Central Otago. The other samples are included only in order to illustrate the influence of protein content on loaf-volume, and, not being representative . of their particular varieties, their names are not given. From a consideration of protein content it was said in- the same article that “ P 467, a sample of White Tuscan, contained a moderate amount of protein ”that is, its strength also would be expected to be moderate only; also that “ the samples of Victor gave generally very good yields of flour, but in 1922 appeared in most cases to be lacking in strength. P 322 was a sample above the average for the variety.”

Fig. 2 shows the results of the baking-tests of these two samples compared with the sample of Velvet (P 290), already illustrated, and a standard sample. The White Tuscan and Victor samples were the best all-round samples of their varieties received in 1922 ; it is fairly obvious that they do not compare favourably with the sample of Velvet, which was in strength only a little above the average for that variety in 1922. As a matter of fact, this sample of Victor is not even such a good wheat as its protein content would suggest. On comparing it with loaf No. 5, Fig. 1 (loaf-volume 434 c.c.*), it will be seen that its loaf-volume (397 c.c.) is less, though it contains over 1 per cent, more protein. This is due to factors which are not discussed in the present article. Loaf No. 4 shows the poor texture of the bread produced from this weak flour. While speaking of Velvet it may be interesting to point out .that another sample of Velvet with protein 14’88 per cent, gave a loaf-volume of 690 c.c. Of some Tuapeka samples it was said in the preceding article that “ Thew . . . contained a very good amount of protein (12-50 per cent.),” and that “ Marquis ... in certain American States fetches highest prices. . . . The milling-yield [of this particular sample] is good, and it still contains a good percentage of protein.” These two flours were baked because they were considered representative of the very interesting wheats obtained from Dumbarton, near Roxburgh, and which were actually grown at the Moa Seed-farm. Fig. 3 fully bears out the foregoing statements. Referring to Fig. 3, for purposes of comparison these samples were photographed alongside the best samples of some other varieties received. Nos. 2 and 4 are obviously much better samples than 3 and 5, and there is no doubt which is of the most value to the miller, the baker, and the consumer.

One interesting point about this series (Fig. 3) is that Marquis, with a smaller protein, content than Thew, yet produced a loaf of larger volume. Here is one of the exceptions to the rule that protein content is a measure of strength. At the same time there is never any doubt as to these .two wheats producing flour of very good quality, even if one is an exception to the general rule. In this baking-test is . perhaps the key to the statement quoted above that " Marquis fetches highest prices.” Atthe time when analytical figures only were available it was stated that one of the outstanding samples milled in 1922 was the sample of Burbank’s Super grown at Flaxton, Eyre County. Its protein content was as high as 14-44 per cent.” The loaf baked from this flour is No. 3, Fig. 4. It will at once be seen that the baking-tests since carried out have quite confirmed the analytical results obtained some months ago. This sample of Burbank’s Super produced a loaf of excellent volume. Alongside it (No. 2) is the poorest sample of wheat received in 1922, containing only 7-69 per cent, protein ; this is illustrated, of course, only for purposes of comparison and of general interest, and is obviously not representative of its variety. No. 4 is the best sample of White Tuscan received at this Laboratory'in 1922, and the loaf on the extreme right is the good sample of Velvet previously referred to. There is not much doubt about Burbank’s Super being one of “ the outstanding samples milled in 1922.” ’

EFFECT OF PROTEIN CONTENT ON LOAF-VOLUME Continued.

[Photos by F. T. Leighton.

GENERAL.

■ In connection with the whole question of experimental milling, of wheat and testing of flours many pertinent questions might be asked. For instance :—

(i.) Does the yield of flour from the experimental mill correspond with the yield obtained when the wheat is milled on a commercial scale ?

(2.) Does the flour obtained experimentally produce on baking a I oaf of good colour, appearance, and palatability ?

(3.) Do the wheats called “ strong ” and “ medium strong ” produce flours comparable with flours of a similar classification in other countries ?

(4.) Are the baking-tests comparable with the results obtained by the baker ? ' ...-.A...

(5:) Does the protein content of a flour bear any useful relationship to the loaf produced ?

It is thought that these and other questions can now be satisfactorily answered, and they will be briefly discussed in the same order.

(1.) It has already been stated that the percentage of ash is an indication of the skill shown in milling. According to various authorities the amount of ash in a straight grade flour (such as is milled in this Laboratory) should be at least 0-48 per cent. ; it is said in effect that if a flour contains less than this amount the flour has not been so thoroughly removed from the grain as when it contains more. On the other hand, if it contains more than 0-90 per cent, ash the wheat has been overmilled.

The whitest flour comes from the centre of the grain ; the strongest and best (the most glutinous) is situated just beneath the covering, which in milling is separated as bran, &c. The miller, concentrates on separating as perfectly as he can this -quality flour from the bran, otherwise microscopic bran-particles will find their way into the flour-stream and reduce its quality, colour, &c. The bran . of the wheat-berry is considerably richer in inorganic substances (compounds of calcium, magnesium, phosphorus, potassium, &c.) than the flour ; if bran therefore finds its way into the flour the inorganic' content of the latter. becomes greater. In determining the ash, one determines the amount of these inorganic compounds ■ present, and in this way obtains an indication of the purity of the flour. ' If the ash is too high, a part of the bran has probably found its’ way into the flour ; if it is too low — the whiter central portion contains not only less protein but also a smaller amount of inorganic. compounds—not enough of the richer outer layer of flour has been removed from the -bran. . .

It will be seen on reference to Table II; published in the preceding article, that none of the samples milled here exceeds the limits mentioned above. Further than this, the flour, if it had not been satisfactorily separated from the outer husk of the grain, would have been - of . a dirty colour, and this would have shown itself in producing a bread of a dirty and disagreeable colour. Looking at this question from still, another point of view, duplicate - and triplicate results of

milling-tests agree as closely as can reasonably be expected (within o-2 per cent.). This being so, it seems that the amount of flour obtained, being constant, is in effect a real measure of the flour available in the grain by milling processes under rigorously maintained conditions.

(2.) In answer to the second question it may be said that in .every case where a flour was tested the bread in the samples above a certain strength has been of good texture when cut, and has possessed a colour as good as that of the commercial “ baker’s ” flour which was baked with each series. The question of colour is interesting from a practical point of view, because in this Laboratory the. mill is provided with nothing • corresponding to ' the ■ elaborate machines for cleaning the grain which form so indispensable and prominent a part of most modern mills ; all cleaning is done here by hand, and at best must be imperfect.

The palatability of the strong samples has been as good as, and often better than, that of ordinary baker’s bread. Externally the loaves were of a pleasing colour and well crusted ; their texture was always found to be good with strong flours, decreasing in quality as the protein content became less, until finally the poorest sample might be said to have had no texture at all.

(3.) As regards comparison with samples of known and accepted good strength in other countries, the information in the .left half of the following table was obtained from Bulletin 177 (1911) of the Kansas State Agricultural College Station. Kansas, it may be mentioned, is one of the leading wheat States of America.

It will be seen that, judged by loaf-volume, strong and mediumstrong New Zealand wheats lose nothing when compared with typical Kansas wheats of the same classes. For purposes of comparison the local figures are calculated on the same amount of flour that was used in the American experiments.

(4.) The method of experimental baking is the method of the baker, and does not differ from his except in special cases to be mentioned. It is essential for purposes of comparison that the tests should give the measure of the strength of the flour and thus reveal differences of quality. Really comparative tests are attained, then, only by very exact control of all the processes and of temperature, no one flour being favoured more than another. A skilled baker no doubt adapts his methods to suit the different flours he uses, and by the processes of kneading and fermenting improves a weak flour. But this does not prevent that, flour from being essentially a weak flour.

and of less value ultimately, not only from the point of view cf breadmaking, but also from that of the extra time and labour necessary to remedy its inherent defects. The experimental baking-test still remains a real criterion of the true value of a flour. (5-) There is no doubt that high protein content is generally associated with high loaf-volume (i.e., flour-strength). This is apparent from the photos and the accompanying’data.

CONCLUSION.

Of the numerous baking-tests made, a selection is given here of those which pointed the moral. They have been used mainly because they were available when the photos were taken, and because also they illustrate the main points of this and the preceding article. • Tests with other samples confirm these results.

It is necessary to point out that, though analogies and comparisons should not be pushed too far, members of a single series are strictly comparable. Where baking-tests are often carried out over a number of weeks, and on days of which some are colder than others, it is evident that exact control of all the conditions is most difficult. For instance, it was found impossible to obtain a compressed yeast which was always of the desired uniform good quality; and it is a well-known fact, too, that the yeast-plant. is very sensitive to small temperaturechanges. The writer can only agree - with the authority who said, “ With all the care and the corrections noted . " . the difficulties of obtaining strictly comparable tests ' are more evident to the one who has made the tests than to any one else/' Baking-tests, however, are undoubtedly of great value, any appreciable differences in quality being at once apparent; and, being practical demonstrations, they are the more convincing on that account.

Variation in Milk Test during Lactation Period. Experience shows that a cow calving in good condition will probably both milk well and test high at the commencement of the milking-period, and that there will be a gradual decline in both milk and percentage of butterfat until the surplus condition is worked off the body and the latter is reduced to normal producing condition. On the other hand, a cow freshening in poor condition may be expected, to give both a light yield of milk and a low test until the body is replenished as the result of more abundant and suitable feed, &c. . There will then probably .be a gradual increase in both test and fat until the maximum fat-production for the season is reached at about the fifth month. Tests at the end of the milking season are found to be influenced by the condition of the cow, the nearness to calving, and the season of the year, and accordingly may fluctuate either up or down.— W. M. Singleton, Director of the Dairy Division.

■ Cheese-colouring. — Last season some difficulty was experienced in connection with the colour in coloured cheese. It was at first considered that the colouring was faulty, and in some instances the trouble disappeared when the colouiingmaterial was changed. In other instances colouring-material ' which when used at one factory produced inferior-coloured cheese was used without any trouble at an adjoining factory. It would appear that some milks have a reducing effect on colour which does not obtain with other milks. The trouble is being investigated bacteriologically by the Department.

* This sample of good average commercial baker’s flour was obtained from a local warehouse. It was assumed, if this sample gave the same loaf-volume each time, that the necessary' conditions were maintained during each baking with the requisite degree of accuracy.

* c.c. = cubic centimetre cubic inch approximately).

Note.The relative sizes of the different loaves are not the same in all the photos —i.e., one photo cannot always be compared with another as regards the apparent loaf-volumes. This, of course, does not apply to loaves in the same illustration.

No. ■ Protein. Half-loaf Volume. . Per.Cent. c.c. I ' . . Per Cent. c.c. . boo 2 ■ 13-19 663 ' 3 •: . 10-94 563 4 9-88 479 5 8-56 434 ■

FIG. I.

No. . W ■ ■ 'Variety. Protein. ■ • Half-loaf Volume. Per Cent. ' ’ c.c. I Commercial “ baker’s ” flour ... ' . . Per Cent. c.c. 7. 600 Q Velvet (P 290) . . ... .... .. . . I.3-I9 ■ 663 3 White Tuscan (P 467) . . 9-88 479 4 Victor (P 322) .. t .- ' .. 9-63 397

FIG. 2.

[Photos by F. T. Leighton.

No. Variety. Protein. Half-loaf Volume. I; Commercial “ baker’s ” flour Per Cent. c.c» 600 • 2 Marquis (P 429) . .' . . 11-44 666 3 White Tuscan (P 467) 9-88 511 4 Thew (P 432) 12-50 600 5 Victor (P 322) . . . . . ' . .. 9-63 397

FIG. 3.

No. Variety. Protein. ' Half-loaf Volume. I Commercial “ baker's ” flour . . Per Cent. c.c. 600 2 Purple-straw Tuscan (P 319) ■■■■ 7-69 352 3 . Burbank’s Super (0 815) . . . . 14-44 .: 726 4 White Tuscan (P 467) ■ ... ... 9-88 511 5 Velvet (P 290) . . I3-I9 663

FIG. 4.

No. Strong Wheats tested in Kansas. New Zealand Wheats. Variety. Protein. Loafvolume. No. Variety. Protein. Loafvolume. • z • • . • Protein. Loafvolume. 58 Malakoff . . Per Cent. I5-65 c.c. 1,330 O815 Burbank's Super . . Per Cent. 14-44 C.C. 1,452. 65 Fife 12-24 1 ,290 P 308 College Hunters . . 12-19 1, 292 67 Minnesota. . 12-62 i>3 10 P 290 Velvet . . I3-I9 1,326 68 Bearded Fife io-68 1,300 P 429 Marquis ,, n-44. 1,332 70 Minnesota. . . 12-22 1 ,260 P 431 Thew . 12-50 .1,200 76 Turkey Red 11-15 1,140 P 259 Dreadnought 10-94 I ,200