Popular Science Monthly/Volume 25/June 1884/Ensilage and Fermentation
By MANLY MILES, M. D.
THE preservation of green fodder in the form of ensilage is now attracting so large a share of the attention of practical farmers, that a brief sketch of the history of the process, and an outline of the known facts in regard to fermentation, must be of interest to the general reader, as well as the student who wishes to trace the laws of evolution in the development of improved methods in agriculture.
Nearly thirty years ago, Adolf Reihlen, who owned a sugar-factory near Stuttgart, in Germany, preserved a crop of fodder-corn, which had been injured by frost, by burying it in trenches or pits, and covering it with the soil thrown out to protect it from the atmosphere. This method of preserving corn-fodder was suggested by the well-known process of making "brown or sour hay" by packing newly-cut grass in pits, which had been practiced for many years by farmers in Europe.
When the pits were opened, several months afterward, the fodder-corn had a greenish color and a peculiar odor, but its value as cattle-food was not apparently diminished. M. Reihlen was so well pleased with the results of his experiment, that he made a practice of "pitting" a quantity of fodder-corn every year, to obtain a supply of succulent feed for his cattle during the winter.
In 1870 M. Vilmorn called the attention of French farmers to the advantages of this method of preserving green fodder, which M. Reihlen had then successfully practiced for many years. The new method was so favorably received and extensively introduced in France, that it soon became known as the French system of ensilage. The application to a new crop of the old system of curing grass as "brown or sour hay" was in fact accepted as a practically new method, which was designated as the "ensilage of maize."
M. Morel seems to have been the pioneer in the practice of the new system, the results of his experience having been published in the "Journal d'Agriculture pratique" of October 19, 1871. Others, encouraged by this report, followed his example, and for several years the "ensilage of maize" was the leading topic of discussion in the agricultural papers of France. In 1877 M. Auguste Goffart published, in Paris, a work on ensilage, giving his experience for several years with silos of masonry above ground, in which the covers of boards were loaded to give a continuous pressure to the mass, and thus exclude the air. The covering and weighting of the silo, as practiced by M. Goffart, was an improvement on former methods, and it appears to be the only point on which he can make a claim of originality. A translation of this work, which has been the standard authority on ensilage, was published in New York in 1878, and had a marked influence on the introduction of the system in this country.
As early as 1873 agricultural papers in Great Britain and America gave occasional brief notices of the preservation of green fodder in pits as practiced in France and Germany, and the process was usually referred to as the "potting" or "pitting" of fodder.
In 1875 three earth-silos were filled with fodder-corn and broom-corn seed, under my direction, in Illinois, with results that were quite satisfactory. These experiments were reported in "The Country Gentleman" in 1876, page 627, together with an account of the experience of several French farmers who had used ensilage on a large scale. In this paper the French terms "silo" and "ensilage" were introduced, as they had a definite meaning not well expressed by any English words, and they are now in common use.
Mr. Francis Morris, of Maryland, who has had the credit of making the first experiments with ensilage in this country, made his first silo in 1876. Others soon followed his example, and now we find silos in every part of the country, and ensilage has become a familiar cattle-food. The first silos, as we have seen, were simple pits dug in the ground, and the soil thrown out was used to cover and protect the ensilage. In many soils these pits served but a temporary purpose; and the next step in their development was a lining of masonry to give the pits a permanent character. From the difficulty of keeping the water out of these pits, in many localities, silos of masonry were made above ground, and these at first were massive and expensive. The next step in advance, which quite naturally followed, was, to substitute a movable cover of boards, with weights to give the required pressure, for the cover of earth which had been used in the less perfect form of the silo. As an air-tight inclosure was found to be the essential condition in the construction of a silo, lighter walls were made as a matter of economy, with good results, and even frames of timber, lined with boards or planks, were substituted for the more expensive structures, with complete success.
A balloon-frame of scantling, of suitable size, covered on the outside with matched boards, and lined on the inside with two thicknesses of one-inch matched boards, with a layer of tarred paper between them, thus securing a practically air-tight inclosure surrounded by a dead-air space as a protection against frost, is, in the opinion of the writer, the best and cheapest form of construction. If the boards and timbers are saturated with hot coal-tar, which can readily be done with trifling expense, the durability of the silo will be very much increased. From the fact that wood is not so good a conductor of heat as walls of masonry, it will be seen, from what follows, that wooden silos may have an important advantage over any others in preserving the ensilage, which, in connection with the saving of expense in their construction, must have an influence in bringing them into general use.
There are many conflicting statements in regard to the value of ensilage as a cattle-food, and it may be that the failure to realize the exaggerated claims that were made for it when, first introduced has resulted in a reaction which naturally leads to a low estimate of its value. It must, however, be admitted that a large proportion of the farmers who have used it are fully satisfied that it is a desirable and valuable form of cattle-food, and many would not limit its use to the winter months. Others speak with less confidence of the results of their experience, and are inclined to admit, with those who are not convinced of the utility of the process, that the acidity which is developed to a greater or less extent, in most cases, is decidedly objectionable. Experience at the condensed-milk factories is claimed to be unfavorable to ensilage as food for cows, and some of them refuse to receive milk from farms where it is fed.
That there are great differences in the quality of the ensilage made on different farms, or even in that made on the same farm in different seasons, there can be no doubt, and these differences must be attributed to variations in the conditions under which the ensilage is made, which must result in corresponding modifications of the process of fermentation. When the influence of these varying conditions, which include the peculiarities of the crop, as well as the method of filling the silo, is so well understood that ensilage of a uniform and desired quality can be produced with certainty, the most important objections that are now made to it will be obviated, and it will readily take its place on the farm as a staple article of cattle-food.
My studies of ensilage have for some time past been directed to methods of preventing acidity and securing a desirable degree of uniformity in quality, and thus far the results are, to say the least, encouraging. The experimental silo at the Massachusetts experiment station was made under my direction, on the plan of the wooden silo described above. It was filled in two and a half days with over seventeen tons of fodder-corn, cut in one and a fourth inch lengths, and thoroughly packed as it was put in. A tight cover made of two thicknesses of planed boards and planks was put on, and loaded with barrels of earth that were estimated to give a pressure of over sixty pounds per square foot. For convenience of access to the interior of the mass, a gas-pipe one and a fourth inch in diameter was driven through a hole in the middle of the cover, to the depth of four feet, the upper end being carefully packed to make a tight connection with the planks of the cover, and the upper end was closed with a plug.
When the cover was put on, September 8th, the temperature was 82° Fahr., two feet below the surface. Observations were made from time to time, of the temperature and rate of settling, as recorded in the following table:
The weights as applied gave a uniform pressure; but the cover, as will be seen from the table, did not settle at a uniform rate. There was a fall of 5° in temperature during the first three days, then followed a gradual but not uniform rise, until the maximum of 87° was reached at the end of the first week. It will likewise be noticed that a variation of but 5° from the initial temperature occurred during the first three weeks after the cover was put on and weighted, and that the fall in the temperature was not uniform.
Experiments were repeatedly made with samples of ensilage, taken through the tube, from the interior of the silo. The samples obtained on the 9th of September swarmed with bacteria, which were remarkably active and rapidly increasing by self-division. After the first few days the indications of rapid reproduction were not so marked, but the activity of the bacteria was not sensibly diminished until the temperature had fallen below 60°, more than two months after the silo was filled. The variations in temperature and in the rate of settling were undoubtedly connected with the vital activity of the bacteria, but the precise relation of these variations could not be traced.
The real significance of these minute organisms can not be fully appreciated without a review, including a brief history, of the known facts of the process of
Fermentation.—The alchemists were acquainted with ferments and fermentation as early as the thirteenth century, but we need not stop to notice their crude theories in regard to the process. In 1659, Willis, an English physician, presented a theory of fermentation, which was revived by Stahl, the originator of the phlogiston theory, in 1697. According to the theory of these philosophers, ferments had a peculiar motion of their particles which they communicated to the particles of fermentable substances and thus produced fermentation. The discovery of carbonic acid by Black (1752), of oxygen by Priestley (1774), and of the composition of the atmosphere and water by Cavendish (1781), laid the foundation for the experiments of Lavoisier, who attempted a quantitative determination of the changes taking place in the transformation of sugar into alcohol. Gay-Lussac (1815) revised the figures obtained by Lavoisier, by less perfect methods, and made a close approximation to a correct formula. In 1828 Dumas and Boullay pointed out and corrected errors in the formulæ of Gay-Lussac, and in this amended form they were, for many years, accepted as an accurate statement of the phenomena of alcoholic fermentation. Afterward, however, the discovery was made that glycerine and succinic acid are constant products of the process, and the formulæ had to be again corrected. These formulæ, even in their amended form, did not take into the account the yeast which had been recognized as an essential element in the process, and theories were formed to account for its action. Berzelius attributed the influence of yeast to a "catalytic" action—mere contact with the ferment being sufficient to excite fermentation in a fermentable substance without any other direct relation. In 1840 Liebig presented a theory of fermentation which was generally adopted by chemists. He recognized fermentation and putrefaction as essentially similar processes. Albuminoid substances, from the complex arrangement of their molecules, were assumed to be in a state of unstable equilibrium tending to decomposition, and their putrefactive transformations, which were communicated to fermentable substances, were the cause of fermentation. He claimed that "yeast produces fermentation in consequence of the progressive decomposition which it suffers from the action of air and water." Fermentation and putrefaction were claimed to be processes of combustion or oxidation. This theory was more fully elaborated, in 1848, by assigning to the decomposing albuminoid ferments a peculiar molecular motion which communicated to fermentable substances a similar vibration of their particles, and a consequent decomposition. This was in fact but a revival of the theory of Willis and Stahl more than two hundred years before. Notwithstanding its general acceptance by chemists, Liebig's theory failed to recognize one of the essential factors of fermentation, and we must now turn our attention to a brief outline of some of the discoveries which disproved it, and furnished on the other hand a complete and satisfactory explanation of the process.
Leeuwenhoek, in 1680, made the discovery that yeast was composed of minute granules, but, with the imperfect lenses of that time, he failed to determine their real character. Fabroni, in 1787, described the yeast-granules as a vegeto-animal substance; and Astier, as early as 1813, claimed that this ferment was endowed with life, and derived its nourishment from the fermenting materials, thus causing fermentation. About 1838 Cagniard-Latour and Schwann, by independent observations, rediscovered the yeast-granules of Leeuwenhoek, and, by means of the better microscopes at their command, succeeded in proving that they were vegetable cells which were reproduced by budding. Schwann, by a series of ingenious experiments, proved that the germs of the living ferments were conveyed to fermentable substances by the air, and that they were the cause of fermentation, while the free admission of oxygen, under conditions that excluded the germs, was without effect. The experiments of Schwann were, in themselves, sufficient to establish the truth of the physiological theory of fermentation, but they were entirely ignored by Liebig and the advocates of his chemical theory. A complete demonstration of the true theory of fermentation was finally made by Pasteur (1857-'79) in a series of experiments which, from the skill displayed in their conception, and the remarkable accuracy secured in conducting them in accordance with strictly inductive methods, may safely be classed among the most brilliant records in the history of science. He repeated the experiments of his predecessors, invented new methods of investigation by which he was enabled to eliminate all possible sources of error, and answered his opponents by an accumulation of experimental evidence that could not be controverted. He proved that sugar was acted upon by a variety of ferments, each giving its own peculiar product, and that the different kinds of fermentation, properly so called, as the alcoholic, the lactic, the acetic, the viscous, the butyric, and putrefactive, were each the result of the vital activity of distinct and specific organisms.
Ferments are now generally divided into two classes: 1. The so-called soluble or chemical ferments, as acids and diastase, which "invert" cane-sugar and transform it into dextrose, or change starch into dextrin. These soluble ferments, according to Dumas, "always sacrifice themselves in the exercise of their activity," but they do not produce fermentation in the strict sense of the term. 2. The true ferments, which, through the investigations of Pasteur, are now known to be living organisms that produce fermentation as a function of their vital activity. Unlike the soluble ferments, these living organisms increase at the expense of the substances fermented. The true fermentations are therefore purely physiological processes, which are defined by Pasteur as "the direct consequence of the processes of nutrition, assimilation, and life, when they are carried on without the agency of free oxygen," or, "as a result of life without air."
The organized ferments, which belong to the class of fungi, may be divided into two groups, the saccharomycetes, or budding fungi—the active agents of alcoholic fermentation, of which yeast may be taken as the type—and the schizomycetes, or fission fungi, which include the lactic, the butyric, and similar ferments, and the organisms that produce putrefaction; most of them are of the form known as bacteria, and they multiply rapidly by subdivision. It is probable that all the members of both groups propagate by means of spores, as well as by their special processes of budding and fission, but there are many species in which reproduction by spores has not been observed. The living organisms (bacteria) found in samples of fresh ensilage belong to the group of schizomycetes. Thus far no members of the group of saccharomycetes (yeast or alcoholic ferments) have been observed, by me, in samples from the interior of the silo that had not been exposed to the air. When a large surface of ensilage is exposed to the air, after the silo is opened, a variety of ferments may make their appearance, and with them several species of molds, but they are evidently produced from germs derived from the air.
The mold-fungi are not included in the class of ferments, as Pasteur has proved that they act as ferments under exceptional conditions only, and even then they do not produce active fermentation. The alcoholic ferments have been studied more thoroughly than the others, from their importance in the manufacture of beer, wine, etc., but many of the facts developed in their investigation are undoubtedly applicable to other ferments.
From Pasteur's experiments with fruits in an atmosphere of carbonic acid, it appears that any vegetable cells which are capable of extracting their needed supply of oxygen from organic combinations may, by this manifestation of their vital activity, act as ferments, and the true ferments are distinguished from these, not by a difference in their specific action, but from the fact that they are capable of carrying on the functions of nutrition and assimilation with much greater activity without a supply of atmospheric oxygen. Pasteur has likewise proved that the alcoholic ferments develop rapidly in the presence of air, but that their function as ferments is impaired by this ready supply of oxygen. In the absence of air, on the other hand, as in an atmosphere of carbonic acid, they take their supply of oxygen from organic substances, as sugar, and their function as ferments is increased. When the life of the bacteria or other organized ferments is destroyed, the processes of fermentation and putrefaction cease, and this takes place at a temperature of from 122° to 140°, according to observations made in the course of the controversy in regard to spontaneous generation. After the organized ferments are killed, fermentation or putrefaction can not take place until the living ferments are again introduced. The canned articles of food which are now so common in the markets are an illustration of the application of this principle. In their preparation heat is applied, which kills the bacteria—the active agents of fermentation—and the cans are then sealed to prevent the introduction of a fresh supply of germs from the atmosphere. The popular notion that canned articles of food are preserved by excluding the atmospheric oxygen, which has been derived from the application of Liebig's chemical theory of fermentation, is without foundation. The experiments of Schwann, Pasteur, and Tyndall conclusively prove that articles which are peculiarly liable to undergo putrefactive changes, as urine, and an endless variety of vegetable and animal infusions, can be kept without change for months and years when abundantly supplied with free oxygen, if proper precautions are taken to exclude the living organisms that are the real cause of fermentation. These experiments have likewise proved that the germs of the bacteria of fermentation and putrefaction are widely distributed in the air, and the supposed cases of spontaneous fermentation, or putrefaction, are readily explained by the "seeding" of the fermenting substances with germs derived from the atmosphere.
As fermentation is strictly a physiological process, the fermented product may be looked upon as the residuum of what is required in the nutritive processes of the bacteria of fermentation.
The variations in the quality of ensilage, to which attention has already been directed, are readily explained by differences in the condition of the crops, as to maturity and development, and the manner in which it is packed in the silo, all of which must have an influence on the performance of the nutritive functions of the bacteria, and corresponding variations will consequently be presented in the residual or fermented product. As in other cases involving the activity of living organisms the molecular changes taking place under such different conditions can not be expressed in any definite chemical formula.
In advocating these views, Pasteur says: "Originally, when fermentations were put among the class of decompositions by contactaction, it seemed probable, and in fact was believed, that every fermentation had its own well-defined equation, which never varied. In the present day, on the contrary, it must be borne in mind that the equation of a fermentation varies essentially with the conditions under which that fermentation is accomplished, and that a statement of this equation is a problem no less complicated than that in the case of the nutrition of a living being. To every fermentation may be assigned an equation in a general sort of way—an equation, however, which, in numerous points of detail, is liable to the thousand variations connected with the phenomena of life. Moreover, there will be as many distinct fermentations brought about by one ferment as there are fermentable substances capable of supplying the carbon element of the food of that same ferment, in the same way that the equation of the nutrition of an animal will vary with the nature of the food which it consumes. As regards fermentation producing alcohol, which may be effected by several different ferments, there will be, in the case of a given sugar, as many general equations as there are ferments, whether they be ferment-cells properly so called, or cells of the organs of living beings functioning as ferments. In the same way the equation of nutrition varies in the case of different animals nourished on the same food, and it is from the same reason that ordinary wort produces such a variety of beers when treated with the numerous alcoholic ferments which we have described. These remarks are applicable to all ferments alike: for instance, butyric ferment is capable of producing a host of distinct fermentations, in consequence of its ability to derive the carbonaceous part of its food from very different substances, from sugar, or lactic acid, or glycerine, or mannite, and many others. When we say that every fermentation has its own peculiar ferment, it must be understood that we are speaking of the fermentation considered as a whole, including all the accessory products. We do not mean to imply that the ferment in question is not capable of acting on some other fermentable substance, and giving rise to fermentation of a very different kind. Moreover, it is quite erroneous to suppose that the presence of a single one of the products of a fermentation implies the co-existence of a particular ferment. If, for example, we find alcohol among the products of a fermentation, or even alcohol and carbonic-acid gas together, this does not prove that the ferment must be an alcoholic ferment, belonging to alcoholic fermentations, in the strict sense of the term, nor again does the mere presence of lactic acid necessarily imply the presence of lactic ferment. As a matter of fact, different fermentations may give rise to one or even several identical products."
From this statement of the physiological conditions that modify the products of fermentation, it must be seen that uniformity in the quality of ensilage can only be secured by preventing fermentation altogether, or confining it within the narrowest possible limits. This can only be done by killing the bacteria of fermentation in the earliest stages of their activity, which would result in the production of ensilage free from acidity, and closely resembling, in quality, the green fodder from which it is made. If the bacteria can be killed, when the silo is covered and weighted, the inclosed mass of ensilage will be practically preserved under the same conditions as fruits, or vegetables, or meats, are preserved when canned.
The practical question, then, presents itself as to how this can best be accomplished. An extended series of observations on the samples of ensilage from the experimental silo have already been made, to determine the temperature required to kill the bacteria which cause the acid fermentations. This will, undoubtedly, vary somewhat with the kind of produce under treatment, and its condition when put in the silo. Thus far my experiments seem to indicate that a temperature of from 115° to 122°, maintained for one or two hours, will be sufficient to kill the bacteria under the conditions in which they are now placed. In this connection attention must be called to the fact that the time of exposure to a given temperature is quite as important as the temperature itself. A given temperature, continued for several days, may have a better effect than a higher one maintained but a few minutes. Again, a degree of heat that will kill the mature and active bacteria will not, in all probability, kill the germs which may produce succeeding generations of active bacteria if the given temperature is continued but a short time.
From the results recorded in the table, it is reasonable to infer that an initial temperature sufficiently high to kill the active bacteria would be continued for several weeks, and this, in all probability, would insure the destruction of any successive generations of bacteria that might be produced from the germs that had not been killed. For this purpose, silos with walls of wood may have an important advantage over those constructed of materials that are better conductors of heat.
In filling the silo, all writers on ensilage agree in giving directions which are based on Liebig's chemical theory of fermentation. The thorough packing of the ensilage as it is put in and the rapid filling of the silo are points that are strongly urged to prevent, as far as possible, the exposure of the fodder to the oxygen of the atmosphere, which is assumed to be the exciting cause of fermentation. In the light of the physiological theory of fermentation it will, however, be readily seen that the living ferments, which produce acidity, are buried with the fodder as it is packed in the silo, and the exclusion of the atmosphere, as Pasteur has proved, is a condition that favors fermentation, the oxygen itself not being directly concerned in the process. When the greatest care is taken in packing the ensilage, the temperature of the mass will often rise above 100° Fahr. (I have observed a temperature of 105° under such conditions); and, when the time of filling is extended over several days, a considerably higher temperature may be developed.
There are good reasons for the belief that, with less packing of the fodder when put in the silo, the time of filling may be safely extended until the temperature rises to a point that is fatal to the bacteria, and this is the probable explanation of the reported cases in which the ensilage is said to be "sweet," or free from acidity.
The efficient cause of this preliminary heating process, or the changes in the fodder involved in its development, have not been determined by experiment, and we do not know the precise conditions under which the best results may be obtained.
In the present state of our knowledge of the subject, the most desirable method may be to fill the silo without any packing, beyond that produced by the weight of the superincumbent mass, and then allow it to remain until the desired temperature is reached, before putting on the cover and weights. The best method can only be determined by carefully conducted experiments, that are made with a full knowledge of the different conditions that may have an influence in modifying the results. It can not, however, be doubted that sour ensilage can only be produced by conducting the process so that the temperature does not rise above the point that is fatal to the bacteria (probably 115° to 120°).
Observations on temperature have been generally neglected when silos were filled, and we, therefore, lack the necessary data for determining the precise temperature required to prevent fermentation, or the most favorable conditions for producing it, from the results of practical experience.
Several cases have been reported to me in which the fodder at the time of filling the silo was supposed to be "spoiled" from the high temperature developed before it was covered and weighted, but on opening these silos, after several months, the result uniformly obtained was ensilage of the best quality, free from acidity. But a single case has, however, come to my knowledge, in which the exact temperature was recorded at the time of filling the silo, when the resulting product was sweet ensilage. Mr. George Fry, of England, reports the results of his experience the past season, which is of particular interest in connection with my experiments with ensilage. He filled a silo with Trifolium incarnatum (crimson clover), "rough grass," and "clover and rye grass," between the 7th and 30th of June, the temperature recorded at the time of covering being 132° six feet from the surface. The cover was weighted with twelve inches of sand. On July 11th, and again on the 17th, the cover was taken off, and the silo was filled with "meadow-grass," to make up for the loss in settling. The temperature observed at these dates was 140° at a depth of six feet. In another silo, filled with clover and "rye-grass" and "meadow-grass," between June 30th and July 11th, when the cover was put on and weighted, the recorded temperatures were (July 7th) 149° and (July 14th) 158°. The first-mentioned silo was opened October 25th, and the ensilage is described as "of a brown color, and of a sweet, luscious odor, free from acidity, very much resembling that of ordinary hay," and it was at once eaten by cattle, sheep, and horses, with apparent relish.
Mr. James Chaffee, of Wassaic, New York, informed me that from unavoidable delays in filling his silo with fodder-corn, in 1882, the ensilage became so "hot," before it was covered and weighted, that he feared it would be entirely spoiled; but, when it was opened in the fall, the fodder was perfectly preserved, of a brown color, and sweet, delicious odor, without the slightest indication of acidity. His cows ate it with such a decided relish that he had no hesitation in saying it was the best ensilage he had ever made. Last year he followed the usual method of rapid filling and thorough packing, and his ensilage, when opened, was very sour, and in quality decidedly inferior to that made in 1882. Other cases of a similar import might be given to show that a temperature sufficiently high to kill the bacteria and prevent fermentation can readily be obtained in the process of filling the silo, and that the ensilage under such conditions is of much better quality than when the temperature is kept within the range that is favorable for the development of the acid ferments.
Experiments are now needed to determine the exact temperatures required for destroying the organisms that cause fermentation, under the different conditions presented at the time of filling the silo, and the special methods of practice that may be desirable in the treatment of different crops. This field of experimental investigation is of the greatest practical interest, and we may safely predict that the thermometer will soon be found as indispensable in securing the best results in the ensilage of green fodder as it is now in the various processes of the dairy.