Jour. Chem. Soc. Trans. 59: 664-677. 1891.
LXIV.—The Influence of Temperature on Germinating Barley.
T. CUTHBERT DAY
It is a matter of common observation that, other conditions being the same, an increase of temperature within certain limits has a stimulating influence on germinating barley.
From a technical point of view, a study of the influence of temperature on germinating barley must be of great importance, seeing what a prominent part it plays in the proper growth of the corn on the malting floors. It was with the intention of throwing some light, however small, on this still obscure subject that I have undertaken the present inquiry.
Experiments have been performed by several investigators as to the influence of temperature on the production of carbon dioxide by germinating seeds: by Sachs in 1865, Laskovsky in 1874, Borodin in 1875, Rischawi and A. Mayer in 1876, and R. Pedersen in 1880. The net result of the investigations is, that the production of carbon dioxide by germinating seeds increases with the temperature. The two last-named experimenters give curves illustrating the results of their experiments.
A knowledge of the amount of carbon dioxide exhaled by germinating barley during growth at various temperatures, as in the process of malting, is undoubtedly of great value, since a definite idea can then be formed of the amount of material decomposed, in order to furnish the gas. A good estimate of the germinative activity at different stages of growth may also be obtained by measuring the carbon dioxide produced at stated intervals. But, from a practical point, of view, an insight into the constitution and properties of the malts produced by growing barleys at different temperatures would be of much greater value. Bearing these considerations in mind, I determined to grow identical samples of barley at different temperatures, after steeping them under precisely similar conditions to ensure identity in the amount of moisture absorbed. The growth was allowed to proceed at a uniform temperature, which was varied in the different experiments, for 10 days. The carbon dioxide produced was weighed from day to day, and at the end of the 10 days the germinated barley was dried at a low temperature, and securely sealed up for future analysis, with the object of gaining some knowledge of the constitution amid properties of the different malts produced.
Method of Experiment—The degree of germination and consequent internal change in the constituents of a barley corn is affected materially by four conditions, namely, moisture, temperature, aeration, and duration of growth. In order to study the effect of temperature, it was of course necessary to secure in the different experiments similarity as nearly as possible in the other conditions of growth. Since the success and trustworthiness of the experiments depend entirely on the method of conducting the germination from first to last, I shall devote some space to a full description of the processes and apparatus employed.
|Fig. 1 is a sketch of the apparatus used for controlling the conditions of germination, and for collecting the carbon dioxide produced.|
1. Four small bottles, the first three containing potash solution and the last one water, for purifying the air supplied to the germinating seed. The delivery tube into each bottle only just dips beneath the surface of the liquid.
2. A small flask containing a few c.c. of distilled water, intended to saturate the air passing through it with moisture, at the same temperature as the germinating corn.
I have found by careful experiment that if barley be germinated in air exactly saturated with moisture, it will not absorb moisture from it even if the root appears to be in need of a further supply. Direct proof of this statement may be obtained by weighing the flask which supplies the moisture passing into the flask holding the germinating corn, and also the moisture passing out as collected in an absorption tube; in this determination of course the air must in the first place be dried. With a few slight variations, it will be found that the loss of weight by the moisture flask is exactly balanced by the gain of weight in the absorption tube.
The employment of air
exactly saturated with moisture is absolutely essential to the success of the
though it neither gives moisture to the growing seed nor takes any from it, the degree of moisture imparted to the seed in the first place, for the purpose of experiment, is preserved throughout the time required.
3. A conical shaped flask (700 c.c. capacity) to hold the corns experimented upon; it will accommodate about 45 grams of steeped barley lying in a layer one corn thick on the flat. bottom. The flat bottom is employed to prevent any self heating of the corn and to secure uniformity in the temperature. The cork of the flask is well covered with tallow, which is found to effectually prevent the intrusion of moisture from without.
4. The exit tube from the germination flask. As it emerges from the flask it is bent downwards, and at the corner where it bends upwards a small descending tube is attached. This tube is designed as a trap to intercept any moisture condensing in the upper part of the exit tube, which might otherwise find its way into the germination flask, and thus vitiate the results. This is a most necessary contrivance.
5. A large galvanised iron vessel holding about 4 gallons, and filled with water, well under the surface of which the flasks 2 and 3 with their connecting tube are immersed. They are kept in place from above by a special holder not. shown in the figure. The temperature of the water is kept constant by a delicate thermostat which regulates the size of the gas flame underneath. Over the gas flame is placed a piece of sheet iron to act as a disperser, and prevent unequal heating of the water vessel. During the course of an experiment, a large piece of flannel is thrown over the upper part of the vessel to prevent radiation and the consequent deposit of moisture on the sides of flask 3.
A separate sketch of the thermostat is given in Fig. 2. It differs from the ordinary mercurial thermostat in having the cylindrical bulb turned up. The upper part of the bulb, shown clear in the figure, is occupied by methylated alcohol (sp. gr. 0825). The shaded portion of the bulb and tube is filled with mercury. Thermostats constructed on this principle are extremely delicate and reliable in their working. I had no difficulty in keeping a constant temperature for 10 days with this arrangement; in fact the temperature never varied more than 0.5° F. either way.
6. A small flask containing strong sulphuric acid and a long U-tube filled with pieces of pumice (previously ignited with sulphuric acid) saturated with strong sulphuric acid to completely dry the air coming from the germinating flask.
7. Two sets of potash bulbs containing strong potash solution to absorb the carbon dioxide exhaled during germination.
8. A U-tube containing pieces of pumice saturated with sulphuric acid to absorb the moisture carried over from the potash bulbs.
9. A small flask holding a little strong sulphuric acid, to act as a guard to 8.
10. The aspirator for drawing air through the whole apparatus, and regulated so as to draw about 7 to 8 litres in 24 hours. The long, booked tube depending from the tap of the aspirator ensured a uniform rate of flow, which was usually about 16 drops per minute.
The efficiency of the apparatus was tested by weighing the absorption apparatus (7 and 8), connecting the different parts, and aspirating air for 24 hours. The gain of the weighed parts was found to be only 0.0018 gram.
The barley employed was a fine yellow Norfolk, harvested in 1885, and dried at 90°F. in January, 1886. The germinations were conducted from February to May (inclusive), 1886.
30 grams exactly of the dry barley (90°F.) were taken for each experiment. Each sample was carefully selected from the same bottle, and all doubtful corns, such as thin, broken, misshapen, or discoloured, were carefully picked out. The weighed samples were steeped in similar quantities of water for 60 hours at 60°F. in a water-bath kept at that temperature by means of a thermostat. The amount of water taken up by the corn in this way about corresponds to the quantity usually required in the malting process. The water was changed twice during the steep. The steep water and washings were collected, boiled down to rather under 100 c.c., made up to that volume exactly at 15.5° C., and the gravity taken. The amount of solids in solution was determined from the specific gravity by using the divisor 3.95, which, if not strictly accurate, is sufficiently near for the purpose.
At the end of the 60 hours' steep, the barley was drained and washed, and the adhering water removed by gentle pressure in a clean cloth. The steeped barley was then weighed. The increase of weight, including the weight of solids extracted during steep, gave the amount of water absorbed. The barley was then transferred to the germination flask. After weighing the absorption apparatus, the parts of the apparatus (Fig. 1) were connected together, all joints being securely tied, and air was continuously aspirated. At intervals of about 24 hours, the time being carefully noted, the absorption apparatus (7 and 8, Fig. 1) was again weighed, the increase in weight giving the quantity of carbon dioxide absorbed. The growth of the barley was continued for 10 days in each case, and the state of germination observed from day to day. Once in 24 hours the flask holding the corn was gently shaken to prevent matting together of the rootlets. At the end of 10 days, the germinated barley was extracted from the flask and weighed to prove that no moisture had been absorbed during the time of germination. It was found that the germinated barley lost a little in weight, the loss in every case being nearly represented by the weight of carbon oxidised to carbon dioxide. The actual loss sustained by the barley is really rather less than this, because rather more oxygen is absorbed than is required for the production of the carbon dioxide. The barley was then dried in an airbath for two days at 120°F., separated from the rootlets, and both were then weighed. The malt was securely sealed up in a small bottle and reserved for analysis.
Six experiments were performed altogether, the germination being conducted at the following temperatures:—No. 1 at 38.3° to 43°F., No. 2 at 50°F., No. 3 at 55°F., No. 4 at 60°F., No. 5 at 65°F., and No. 6 at 70°F. These temperatures were maintained throughout the germinating period in each experiment. Experiment No. 1 should have been conducted at 40°F. exactly, but I had some difficulty in regulating the temperature at so low a point.
The Production of Carbon Dioxide.
Experiment 1.—30 grams of dry barley (90°F.)
= 25.482 grams absolutely dry.
Water absorbed during steep, 15.33 grams. Temperature during growth, 38.3° to 43°F.
|State of germination|
|1||23 1/2||0.0310||1.3||No signs of growth.|
|3||22||0.0246||1.1||Just beginning to bud.|
|4||24 1/2||0.0560||2.3||Buds considerably increased in size.|
|5||25 1/2||0.0591||2.3||In full bud, one corn showing a rootlet.|
|6||221/2||0.0495||2.2||Many corns breaking bud and showing a short single root.|
|7||25||0.0553||2.2||Most corns had a short single root rather longer than yesterday.|
|8||22 3/4||0.0597||2.6||Root lets rather longer, some corns showing additional short rootlets.|
|9||24 1/2||0.0651||2.7||Rootlets a little increased in length.|
|10||24||0.0773||3.2||Rootlets rather increased in length, fresh and white.|
Experiment 2.—30 grams of dry barley (90°F.)
= 25.482 grams absolutely dry.
Water absorbed during steep, 15.04 grains. Temperature during growth, 50°F.
|State of germination|
|I||23||00432||1.8||Just commencing to bud.|
|3||24||0.1286||5.3||Most corns with two or three short roots.|
|4||21||0.1436||6.0||Root considerably increased, white and strong.|
|5||21||0.1464||7.0||Growing steadily, spire beginning to show under husk.|
|6||25||0.1747||7.0||Root strong, increased in length.|
|7||24||0.1693||7.0||Growing steadily, spire about half up.|
|8||231||01640||6.9||Root increased in length, spire about half up.|
|9||24||0.1646||6.9||Root a good length, spire about half up.|
|10||24*||0.1511||6.2||Root fresh and
strong, about equal in length to an ordinary
7 or 8 day couch; spire about half up.
Experiment 3.—30 grams of dry barley (90°F.) =
24.82 grams absolutely dry.
Water absorbed during steep, 15.35 grams. Temperature during growth, 55°F.
|State of germination|
|2||24||0.1257||5.2||Most corns showing a short root.|
|3||26 1/2||0.2132||8.0||Root much increased.|
|4||23 1/4||0.2075||8.9||Root, considerably increased, spire showing under husk.|
|5||22||0.2040||9.3||A long, white root, spire nearly half up.|
|6||25||0 .2306||9.2||Root increased in length, spire nearly half up.|
|7||23 3/4||0.2274||9.6||A long, fresh root, spire half up.|
|8||25 1/4||0.2341||9.3||Root still increasing, spire a little more than half up.|
|9||22 1/2||0.1930||8.6||Root. still strong and fresh, spire half to two-thirds up.|
|10||24 1/4||0.2020||8.3||Root long and fading slightly, spire half to fully up.|
grams. of dry barley (90°F.) = 25.482 grams absolutely dry.
Water absorbed during steep, 14.98 grams. Temperature during growth, 60°F.
|State of germination|
|I||23 1/4||0.0897||3.9||Nearly full bud.|
|2||21 1/4||0.1975||9.1||Beginning to make root.|
|3||25 1/2||0.2619||10.3||Root increasing rapidly.|
|4||25||0.2794||11.2||Root growing rapidly, spire about one-third|
|5||23 3/4||0.2436||10.3||up. Strung white root, growing fast; spire half up.|
|6||21 3/4||0.2170||10.0||Root healthy and growing, spire one-third to two-thirds up.|
|7||26||0.2299||8.8||A long, healthy root, spire one-third to nearly up.|
|8||23 1/2||0.1894||8.1||Root still healthy, spire half to full up.|
|9||24||0.1785||7.4||Root beginning to fade a little, spire half to full up.|
|10||24 1/4||0.1748||7.2||Root long and
slightly faded, spire half to full up.
One corn with a little blue mould.
grams of dry barley (900 F.) = 25.482 grams absolutely dry.
Water absorbed during steep, 15.00 grams. Temperature during growth, 65°F.
|State of germination|
|1||23||0.1397||6.1||Breaking bud and showing a single root.|
|2||21 3/4||0.2682||12.3||Very rapid growth of root. Many corns with two or three long roots.|
|3||24 1/2||0.3135||12.8||Root still growing rapidly.|
|4||25||0.3164||12.7||Root considerably increased, spire about half up.|
|5||23 1/2||0.2548||10.8||A long, curly, healthy root, spire half up.|
|6||23 1/2||0.2329||9.9||Root still growing and healthy, spire rather more than half up.|
|7||23 3/4||0.2136||9.0||Root still healthy, but slightly faded, spire about two-thirds up.|
|8||26 1/4||0.2025||7.7||Root very long and still healthy, but a little faded; spire half to three-quarters up.|
|9||21 3/4||0.1885||8.7||Root a little more faded.|
|10||27 1/4||0.1774||6.5||A long root, still healthy, but a little faded; spire half to fully up.|
Experiment 6.—30 grams of dry barley (90°F.)
= 25.482 grams absolutely dry.
Water absorbed during steep, 1538 grams. Temperature during growth, 70°F.
|State of germination|
|1||22 1/4||0.1541||6 9||A short root on most. of the corns.|
|2||23 1/4||0.3262||14.0||Most corns with several short roots.|
|3||23||0.3333||14.5||Quite a bushy root,
strong and fresh looking;
spire one-third up.
|4||24 3/4||0.2959||12.4||A long, curly root, spire about half up.|
|5||22 1/2||0.2531||11.2||Root strong and vigorous, spire half up.|
|6||23 1/2||0.2344||10.0||A good root, spire half to two-thirds up.|
|7||26||0.2403||9.2||Root rather longer and still fresh, spire about two-thirds up.|
|8||23 1/4||0.2140||9.2||Root long, still healthy; spire half to fully up.|
|9||23 1/2||0.2146||8.4||Root still fairly fresh, spire half to fully up.|
|10||24 1/4||0.2181||9.0||Root a little faded, spire half to fully up.|
The figures given in the foregoing experiments show plainly the effect of temperature on the production of carbon dioxide by germinating barley. The most striking feature is the rapid increase in the evolution of the gas during the first few days of growth, as shown by the amount produced per hour each day, especially at the higher temperatures. As the temperature is raised, the maximum evolution takes place at an earlier stage of germination.
I give three series of curves, at the end of the paper, the first showing the progress of the evolution of carbon dioxide from day to day from start to finish in each experiment; the second series, the evolution in milligrams per hour each day for each experiment; and the third series consisting of two curves combining the six experi. tnents, and showing the total production of carbon dioxide and of dry root at the different temperatures. An inspection of these curves will show more plainly the effect of temperature during germination than any number of figures, however carefully arranged.
To begin with Series I, it will be noticed that, as the temperature is raised, the curves tend to lie closer together, showing pretty clearly that, as the temperature rises, the corresponding increase in the production of carbon dioxide tends to diminish. The next point, to be observed is the character of the curves themselves. The three lowest curves have their convexity, generally speaking, turned towards the horizontal line, while the three highest curves have their convexity turned in the opposite direction.
|CURVES SHOWING THE PRODUCTION OF CARBON DIOXIDE, IN GRAMS, BY GERMINATING BARLEY AT DIFFERENT TEMPERATURES. THE NUMBERS OPPOSITE THE CURVES REFER TO THE EXPERIMENTS FROM WHICH THEY WERE OBTAINED.|
|CURVES SHOWING THE
PRODUCTION OF CARBON DIOXIDE IN MILLIGRAMMES PER HOUR FROM DAY TO DAY, BY
GERMINATING BARLEY AT DIFFERENT TEMPERATURES.
THE EXPERIMENTS TO WHICH THE CURVES REFER ARE DENOTED BY THE NUMBER ON EACH CURVE.
|CURVES SHOWING THE
PRODUCTION OF CARBON DIOXIDE AND DRY ROOT
AT DIFFERENT TEMPERATURES IN ALL SIX
CURVE I. RELATES TO WEIGHT OF CARBON DIOXIDE IN GRAMS.
CURVE II. RELATES TO WEIGHT OF DRY ROOT IN GRAMS. THE FIGURES ON THE CURVES REFER TO THE DIFFERENT EXPERIMENTS.
The curves given in Series II show, in a remarkable way, the rate of production of carbon dioxide for each day as measured in milligrams per hour. In Experiment 1, at 40°F., allowing for the small variations of temperature in this case, the rate of production of dioxide gradually increases from start to finish. In Experiments 2 and 3, at 50 and 55°F. respectively, the evolution of the gas increases till the fifth day of growth, after which, practically speaking, it remains on a dead level, though a slight falling off is noticed towards the end. The curve for Experiment 4 shows the greatest production of carbon dioxide on the fourth day, after which period the rate of evolution steadily diminishes. In Experiments 5 and 6, at 65° and 70°F., the evolution of the gas, though very rapid at first, reaches it highest point rather earlier; for No. 5, between the third and fourth days, and for No. 6 on the third day of growth. In both these experiments, the rate of decrease from the maximum is seen to be pretty rapid to the close.
An inspection of the curves given in Series III, comparing the total quantity of carbon dioxide produced in the six experiments with the weight of dry root formed, shows some degree of similarity in their form. Each bend of the one has a counterpart in the other. The chief point to be noticed, however, is that, though there is a considerable falling off in the increase of the quantity of carbon dioxide produced when the temperature rises above 55°F., yet the effect of the increase of temperature above the same point in diminishing the increase in the weight of dry root formed is very much more marked, as the curve plainly shows by the sudden bend at this point towards the horizontal. I shall refer more particularly to this peculiarity in these two curves when I come to consider the constitution of time different malts.
I will now give the results of the experiments as they relate to the weight of malt and root obtained, the carbon oxidised, and the loss during steep, &c.
It will be seen from the figures in the following table that the amount of malt obtained decreases as the temperature is raised, up to 65°F., a slight increase being shown at 70°F. over the quantity at 65°F.
The amount of root increases up to 65°, and at 70°F. a slight decrease is observed.
The quantity of carbon oxidised increases with the temperature all through the series.
The six malts obtained were carefully analysed by methods or modifications of methods chiefly due to Mr. C. O'Sullivan, and published in the Transactions of the Chemical Society.
38.3° to 43°F.
|Absolutely dry malt||24.495||23. 258||22.553||22.435||22.171||22.194|
|Loss in steep||0.220||0.280||0.272||0.252||0.190||0.240|
|Absolutely dry barley||25.4820||25.4820||25.4820||25.4820||25.4820||25.4820|
|Loss, mostly due to
water liberated by
probable combustion of carbohydrates
The following determinations were made and calculated to the dry malt; and from the numbers thus obtained, the results were calculated to the corresponding quantity of dry barley
The numbers obtained under 9 are intended to convey some notion of the diastatic activity of the different malts. The amount of the starch conversion products due to the action of the diastase in the malt on its own starch at a low temperature (40° C.) is found by deducting the sum of the percentages of sugars, of soluble carbohydrates other than sugars, and of the permanently soluble nitrogenous compounds from the percentage of solids dissolved by water at 40° C., as. found under 8.
These figures show either that the malts possess different diastatic powers, or that the starches present in the malts are in such a condition as to render them susceptible to the action of diastase in very different degrees. For my own part, I am inclined to favour the first supposition, namely, that the amount of starch conversion products found was due to the activity of the diastatic ferment in each case.
I append here the figures obtained in the analyses of the six samples of malt produced in the experiments (p. 676).
An examination of the figures relating to the composition of the dry malt reveals a decided difference in their character throughout the series. Taking the different constituents determined in the order they are set down, the fats appear to decrease in quantity, gradually, as the temperature of germination is raised. The sugars increase (with a jump in the first 10 degrees) up to 55°F., after which the amount found is less, though slightly higher at 70°F. than at 65°F.
The soluble carbohydrates other than sugars increase, as in the case of the sugars, very rapidly at first; at 50°, 55°, and 60°F. they remain practically unaltered; but at 65° and 70°F. they show a falling off in quantity. The starch decreases rapidly between 40° and 50°F., and at 55°F. still shows a decided decrease. The figures show an increase from this point up to 70°F. The quantity of cellulose tends to decrease as the temperature rises. The permanently soluble nitrogenous compounds show an increase up to 55°F., but beyond this point up to 70°F. there is a gradual decrease. The coagulable nitrogenous compounds are present in small quantity; there is a gradual increase up to 60°F., above which temperature rather less is found. The starch conversion products formed by digesting the malts with water at 40° C. follow the same rule as the permanently soluble nitrogenous bodies, showing a maximum at 55°F.
The most important point brought to light by a consideration of these results is, that the sugars reach their maximum, the starch suffers the greatest amount of degradation, the permanently soluble nitrogenous compounds are present in greatest quantity, and the diastatic ferment is the most active, all in the malt grown throughout at a temperature of 55°F. The evidence as to the peculiar change in the composition of the malts which were grown at a temperature above 55°F. is strongly corroborated by the determination of the carbon dioxide and dry root formed. A mere inspection of the two curves in Series III demonstrates clearly enough that there must be some remarkable change at the above-mentioned point. It appears, also, as if, at the higher temperatures, a portion at least of the carbon dioxide was produced more at the expense of the sugars and other soluble carbohydrates, formed at the earlier stages of germination, than that the starch alone, by its oxidation, furnished the whole of the gas.
|I.—Calculated on the Dry Malt.|
other than sugars
soluble at 40° C.,
soluble after boiling.
N x 6.33
soluble at 40° C.
coagulated on boiling
soluble at 40° C.
by action of diastase
at 40° C.
to dry malt
|p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.|
|II.—Calculated on the Dry Barley.|
|p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.||p. c.|
The numbers showing the composition of the malts as calculated to dry barley (II) from the proportions given in the first table (p. 674) are chiefly useful in furnishing a test as to the general accuracy of the determinations.
If we add together the numbers representing the sugars, soluble carbohydrates other than sugars, starch cellulose, and carbon oxidised reckoned as C6H10O5, we ought to obtain numbers showing a small decrease from 40°F. up to 55°F. sufficient to allow for the carbohydrates formed in the rootlet; but above 55° F. the numbers should be nearly the same, though least at 65' F., where the maximum amount of root was obtained.
An application of this test gave the following results
|Carbon as C6H10O5||1.28||3.28||4.54||4.97||5.57||5.98|
These totals turn out nearly as expected, though No. 5 appears to be rather too low as compared with the others. On the whole, considering the nature of the analyses and the probable individual differences in the samples of barley grown, the result may be considered as highly satisfactory, and as affording fairly reliable testimony to the value of the experiments. Of course, the totals above given are partly derived on the assumption that the whole of the carbon dioxide formed during germination is derived from the oxidation of a carbohydrate of the empirical formula C6H10O5; whereas I am inclined to infer, from a consideration of the analytical results, that a small part of this gas, especially at the higher temperatures, is probably derived from the nitrogenous compounds, both soluble and insoluble, present in the barley.