BACTERIA AND BUTTER MAKING.
In the making of butter it is necessary to concentrate the milk fat
into a small volume. This process, known as creaming, may be
accomplished by gravity, if the milk is allowed to stand
undisturbed, the fat globules rising slowly to the surface. Much
more rapid separation may be secured, by placing the milk in a
rapidly revolving container in which it is subjected to centrifugal
force, which causes the heavier parts of the milk to pass to the
outside of the bowl, while the lighter part, the fat, collects at
the center of the revolving bowl. There is an enormous number of fat
globules in milk, over 5,000,000,000 in each cubic centimeter, and
as these move through the milk serum, they carry with them many of
the bacteria. The cream is thus much richer in bacteria than is the
skim milk, or even the milk before separation. Besides the
mechanical separation in the manner described, the method of
creaming is of importance, in determining not only the number but
also the kind of bacteria in the cream.
=Methods of creaming.= In the shallow-pan method of creaming, the milk
is kept at ordinary room temperatures. These temperatures favor
especially the growth of the acid-forming bacteria. The milk is
usually sour by the time the cream is removed from it; consequently,
the bacterial content of the cream is high. Moreover, the cream is
exposed to air contamination, and is thus seeded with molds, and
those forms of bacteria that are always found in the air. The cream
obtained in this manner is likely to contain not only numerous
bacteria, but a great variety of forms, some of which undoubtedly
are the cause of the poor keeping qualities of butter made from such
cream.
In the more modern method of gravity creaming, in which the milk is
placed in deep narrow cans kept in cold water, the conditions are
not favorable for the growth of acid-forming bacteria. If the milk
is produced under clean conditions, and is placed in cold water at
once, the bacterial content of the cream will be low, and it will be
less likely to contain undesirable forms than the cream which is
obtained from the shallow pans.
In separator cream the bacteria will be represented by the kinds
present in the milk at time of separation. If this milk is quite
old, the cream will contain large numbers of bacteria; if, however,
early separation is made and the milk is clean, the bacterial
content of the cream will be low.
=Types of butter.= Butter may be divided into two types--acid or
sour-cream, and sweet-cream, depending upon whether the cream is
allowed to undergo the acid fermentation or not before it is
churned. In southern Europe, it is the custom to churn the cream as
sweet as possible, and the resulting product possesses only the
natural, or primary milk flavor. To one accustomed to butter made
from sour or ripened cream, this taste is flat, and if the butter is
free from salt, may remind one of grease. Sweet-cream butter has a
delicate flavor when it is made from good milk, and the taste for it
is rapidly acquired. In some centers, as in Paris, the market
demands this type of butter quite exclusively.
If the cream is allowed to undergo the acid fermentation before
churning, the butter has a much higher degree of flavor and one that
differs materially in kind. Under primitive methods, it was
difficult to keep the cream sweet until it could be churned. On the
small farm with gravity creaming in shallow vessels and infrequent
churning, the cream was certain to be sour when churned.
Undoubtedly, the making of butter from sour cream came into use
because of its greater convenience; people became accustomed to
sour-cream butter, and at the present time it is used in the greater
part of the world, and is the type made in all of the great dairy
countries.
=Ripening of cream.= In modern dairy practice the souring of the cream
is called the _ripening_ process, and is, where the best methods are
employed, largely under the control of the butter maker. The changes
that go on in the ripening process are the same as have been
discussed in the acid fermentation of milk. The increase in acid is
accompanied by an enormous increase in the number of bacteria; the
ripe cream will contain hundreds of millions of bacteria in each
cubic centimeter. The effect of this germ life is to improve or
injure the butter, depending upon the class of bacteria to which it
belongs. The problem of the modern butter maker is to control the
kinds of bacteria growing in the cream.
The temperature at which cream is held during the ripening process
is favorable to the growth of the acid-forming bacteria; hence, in
ripe cream, they are practically the only kind of bacteria to be
found. It must be remembered however, that there are different
classes of acid-forming organisms, some of which produce desirable
flavors, while others are distinctly harmful.
The intensity of flavor of butter is, in a general way, directly
related to the amount of acid that is formed in the cream. A low
acidity at time of churning is usually associated with a mild
flavor, while a higher degree of acidity, up to a certain point,
imparts a more pronounced flavor to the product. If cream is
over-ripened, the quality of the flavor is seriously impaired.
In determining the acidity of cream, a definite volume is taken, and
the acidity determined by titration, expressing the results as such
a per cent of lactic acid. Manifestly, the amount of fat in the
cream influences the apparent per cent of acidity. The acidity will
not usually exceed 0.5 to 0.7 per cent, but in reality the serum
will contain more than this, as the acid is formed in the serum, the
butter fat having no role whatever. In a very rich cream, 40 to 50
per cent fat, it is impossible to develop more than 0.4 to 0.5 per
cent of acidity, and the flavor of the butter will be low, because
of the relation between the amount of acid and fat, while in a thin
cream having the same acidity, the ratio between the amounts of fat
and acid will be very different. For example, in one hundred pounds
of 50 per cent cream of 0.5 per cent acidity there will be one-half
pound of acid and fifty pounds of fat; in the same quantity of cream
containing 20 per cent of fat and having an acidity of 0.5 per cent
there will be one-half pound of acid to twenty pounds of fat. The
flavor of the butter from the rich cream will be quite different in
intensity from that made from the thinner cream.
The acidity of cream cannot be determined with any degree of
accuracy by the taste or odor. Every butter maker should have some
method of determining the degree of acidity in his cream, so that he
may better control the flavor of his product. Several methods have
been devised for this purpose and the necessary apparatus is sold by
all dairy supply houses.
The effect of the ripening of the cream is shown not only in the
flavor of the product, but in a number of other ways. Sour cream
churns more easily, and more exhaustively than does sweet cream. It
is supposed that the fat globules are surrounded by a film of
albuminous material which prevents their coalescing readily. During
the ripening process, the action of the acid apparently dissolves
this enveloping substance, and the globules cohere more easily in
the churning process.
When raw cream is used the ripened-cream butter keeps better than
that made from sweet cream. In sweet cream there are few lactic
bacteria, the majority of the bacteria present being of various
kinds, many of which may be injurious, so far as the keeping quality
is concerned. In sour-cream butter the lactic bacteria make up over
99 per cent of the bacteria present, and their presence tends to
prevent the development of undesirable non-acid forms.
=Source of butter flavor.= The flavor of ripened-cream butter has been
shown to be directly connected with the acid-fermentation of the
cream. The amount of lactic acid formed from the sugar fermented is
dependent upon the kind of bacteria present. The acid-producing
organisms that are desirable from the standpoint of the butter maker
form comparatively small amounts of other by-products, but these
undoubtedly affect the flavor of the butter. As fats have the power
of absorbing odors, the butter fat absorbs some of the by-products
of the acid fermentation, thus acquiring a certain aroma and
flavor.
It is not necessary that the cream be ripened, in order to have the
fat acquire a flavor, for if sweet cream is churned with a
considerable proportion of sour milk, the butter will have much the
same flavor, both as to intensity and kind, as though the cream had
been allowed to sour naturally. A process of butter making known as
the LeClair method is based on this principle. The flavor-producing
substances can also be absorbed by the butter after it is churned,
by working the butter in contact with sour milk. Attempts have been
made to add pure lactic acid to the cream, instead of allowing the
acid to be formed by the bacteria, but while the physical effect on
the cream is the same, the flavor and aroma of the butter are
deficient, because the acid itself does not supply the necessary
aromatic products. This emphasizes the importance of the by-products
of the acid fermentation other than the lactic-acid.
In the past numerous attempts have been made to find organisms that
might be added to the cream, in order to produce the delicate flavor
characteristic of the best type of butter. Some bacteriologists have
claimed that the source of the flavor-giving substance was to be
found in the decomposition products of the nitrogenous constituents
of the milk. None of these attempts have stood the test of practical
use in creameries, and it has been demonstrated that the finest type
of butter can be made by the use of lactic bacteria alone. Formerly,
when butter was made wholly from cream soured under natural
conditions, a much higher degree of flavor was developed. Under
present market demands, a less pronounced flavor is desired, a
condition more readily met by the use of modern methods.
=Importance of butter flavor.= The importance of flavor in determining
the commercial value of butter is evidenced by the relatively high
value placed upon this factor in scoring, viz., flavor, 45 points;
body or texture, 25 points; color 15; salt 10; and package 5 points.
The factors on which butter is judged, are with the exception of
flavor, wholly under the control of the maker, but as the production
of flavor is dependent on the kind of bacteria present in the cream,
it is a far more difficult matter to control, and yet it is of the
utmost importance in determining the value of the product.
The flavor of the butter is dependent on the quality of the cream.
If this is dirty and sour, the maker has little control over the
type of fermentation, and hence, little control of the flavor of the
butter. This has led in some cases to the grading of the cream,
basing the division on the acidity, flavor, and fat content. Such
practice is entirely justifiable, as a better quality of butter can
be made from fresh, sweet cream than from that already fermented. It
is noteworthy that the quality of butter has not improved since the
introduction of the centralizer system, in which cream is shipped
for long distances.
=Control of the type of fermentation.= In the older methods of butter
making, there was little or no control of the type of fermentation
that took place in the cream. Where milk is produced under clean
conditions, and kept at ordinary temperatures, it will generally
undergo fermentation changes, due to the desirable type of
acid-forming organisms. In milk, which is less carefully handled,
the undesirable bacteria are more abundant and the quality of the
butter of lower grade. When butter was made on the farm, before the
development of the factory system, it was not a question of vital
importance whether the product was uniform from day to day, but
with the advent of the modern creamery, turning out thousands of
pounds of butter per day, and with the extension of the markets for
the product, the question of uniformity came to be of much
importance. A uniform product can be secured only by the control of
the type of fermentation in the cream, or by the control of the
kinds of bacteria that cause the souring of the cream. Modern
methods of butter making have been devised on the basis of an
improvement in the ripening process.
=Starters.= From the earliest practice of allowing the cream to stand
until sufficient quantity had accumulated for churning, it was only
a step, but a most important one, to the addition of sour milk, sour
cream, or butter milk, to hasten the ripening process. This was the
beginning of the modern starter. Experience demonstrated that the
addition of these already fermented liquids exercised a desirable
effect upon the production of butter flavor, even though, at that
time, the phenomenon of milk fermentation was not satisfactorily
understood, and the relation of bacterial by-products to the
production of flavor in butter was not recognized.
As a result of experience alone, improvements in the development of
the "home made" starter took place. By careful selection of clean
milk, and the natural fermentation of this under carefully
controlled conditions, as well as the control of the temperature of
the cream during the ripening, improvement in the technique of cream
ripening gradually developed. More and more attention was given to
the preparation of the starter, and its propagation from day to day,
under conditions which would prevent its deterioration. This method
of utilizing naturally fermented milk or cream was gradually
extended, until it became almost universal in the larger
butter-producing districts.
In 1890 a more refined and scientific process was introduced by the
Danish bacteriologist, Storch. Recognizing the fact that butter
flavor was attributable to the development of the bacteria present
in the ripening cream, he conceived the idea of isolating the
various types of organisms found in milk and testing them as to
their effect on the quality of flavor. Selection was then made of
the most favorable flavor-producing types, and these were propagated
in suitable culture media, such as skim milk, which was rendered
more or less perfectly sterile by pasteurization or sterilization.
Under such conditions the addition of a selected ferment could be
made to the fresh cream, and so control the type of fermentation
which occurred therein. An essential requisite in any organism used
for this purpose must be the ability to produce relatively large
amounts of acid rapidly at ordinary ripening temperatures, and also
to form sufficient quantities of the proper flavor-producing
substances to impart a suitable flavor to the butter fat. Such
starters are known as pure culture or commercial starters, and are
prepared in both liquid and dry form. At present they are used to a
greater or less extent in all of the leading dairy districts.
Liquid starters consist of a mass of sterile nutrient medium, milk
or beef broth, inoculated with the pure culture. The dry starters
are made by adding liquid cultures, containing the growing bacteria,
to some absorbing material, such as milk sugar, milk powder, or
starch, the whole mass being dried at low temperatures, so as not to
injure the bacteria. Under such conditions the bacteria, exist in a
dormant state, and are protected from their own by-products, to
which they would be exposed if maintained in liquid cultures. The
keeping quality, therefore, of dry cultures, is much better than
that of liquid cultures.
By the use of the pure-culture starters, the butter maker is able to
add to his cream the same kind of bacteria from day to day, and the
butter will be more uniform than when the less constant home-made
starter is employed. In cream to which the starter is added, there
are present a greater or less number of acid-forming bacteria,
depending upon the age of the cream, and upon the condition under
which it was produced. These will grow during the ripening process,
and the flavor of the product will be the result of the mixture of
the bacteria in the cream. The maker can not, therefore, be certain
that the addition of a pure culture to raw cream will effectively
control the type of fermentation. This can be secured only by first
destroying the existing bacteria in the cream, before the selected
culture is added. Heating the cream accomplishes this; and in cream
thus freed from the various kinds of bacteria, the butter maker can
insure the dominance of the desirable types, contained in the
pure-culture starter. If the cream can be obtained in a sweet
condition, the maker through this process of pasteurization, and the
use of pure cultures, secures almost perfect control over the type
of fermentation that occurs in the cream, and thus exercises control
over the degree and kind of flavor of the product. This most
scientific type of butter making is now used by the most progressive
butter makers in the leading butter-producing regions of the world.
Pasteurization of the cream also distinctly improves the keeping
quality of butter, a condition doubtless due to the freedom of the
same from organisms other than the lactic bacteria. This is a factor
of as much importance as uniformity, because under modern business
conditions, the surplus production must be kept in storage, and it
is essential that the quality should not deteriorate materially
during this time.
=Process of pasteurization for butter making.= In the pasteurization
of market milk, it is necessary to take into account the effect of
heating on the physical and chemical properties of the milk, and the
degree of heat that can be employed is limited. In pasteurizing
cream for butter, there is no such limitation, and the cream may be
heated to any temperature desired. In Denmark where the process of
pasteurization has been used most extensively, temperatures ranging
from 176 deg. F. to 190 deg. F. are used. The machines are of the
"continuous flow" type, and the cream rather than the whole milk is
treated. To prevent the spread of tuberculosis and other diseases,
the Danish government requires that all cream and milk be heated to
176 deg. F., before the skim milk or butter milk is returned to the
farms.
The heating of the butter fat to high temperatures has an injurious
effect on the texture of the butter, unless the cream is cooled to
50 deg. F., for a period of at least two hours previous to churning.
=Propagation of starters.= As has been previously shown, the quality
of butter depends on the kind of bacteria in the cream or in the
starter added. The commercial starters contain lactic acid bacteria
that have been selected with especial care; most of the starters now
sold contain but a single kind of bacteria; hence, are often called
pure-culture starters. The package purchased contains but a small
quantity, and before the starter can be used in the ripening of
cream, it must be increased in amount. It must also be propagated
from day to day so that a fresh starter shall be available daily for
addition to the cream. The propagation of the starter must be done
with especial reference to keeping it in good condition and in as
high a state of purity as possible.
In the past the starter was propagated, by adding the contents of
the bottle purchased to a small amount of milk that had been heated
and cooled; this, if kept in a warm place, would be curdled in
twenty-four hours, and could be used for the inoculation of a large
mass of milk, that had been treated in a like manner, and which,
when curdled, was added to the cream; a small amount was saved for
the purpose of again inoculating a mass of milk that had been heated
and cooled. Following this method it was very difficult to keep the
culture from becoming contaminated with other forms of bacteria.
More recently the most successful butter makers have propagated the
so-called "mother starters" in small vessels, and have used the
larger mass of starter for the inoculation of the cream alone.
Glass vessels are preferable for the propagation of the mother
starters since they are impervious and through the transparent wall
the condition of the ripened starter can be more easily determined
than in a metal or earthenware vessel. An ordinary milk bottle with
an inverted tumbler for a cover, to protect the starter from
contamination from the air, is a most convenient vessel.
The starters may be propagated either in whole or skim milk; the
former is preferable since, in most creameries, it can be more
easily selected. The quality of the milk used has much to do with
the quality of the starter; it should be as fresh and clean as it
is possible to obtain. The clean bottle should be filled half to
two-thirds full, covered and heated in some manner so that the milk
shall be at a temperature close to the boiling point for fifteen to
twenty minutes. The heating may be done by placing the bottles in
water, which is heated on a stove or by steam, or the bottles may be
subjected to streaming steam. The milk is cooled quickly and the
contents of the package purchased added and well mixed with the
milk. In the case of the dry starters, the mixing should be done
with especial care. The bottle is kept in a warm place and in
twenty-four to thirty-six hours, the milk should be curdled. A
second bottle must be treated as before and inoculated from the
first, and the process repeated daily since the bacteria must have
fresh food, if they are to be maintained in good condition.
In order to accomplish this, the maker must be able to maintain
constant conditions from day to day, especially with reference to
the amount of the ripened starter that is transferred to the fresh
bottle of milk, and the temperature at which the bottles are kept. A
spoon, arranged as shown in Fig. 31, enables one to carry a definite
amount of the ripened starter to the bottle of milk to be inoculated
and a constant temperature box (Fig. 32) permits of the maintenance
of the same temperature from day to day. Through careful supervision
of these points, and by taking care at every step to avoid the
introduction of contaminating organisms, the purity of the culture
can be maintained, and the bacteria kept in a healthy condition.
The starter is used because of the acid-forming bacteria it
contains; it is said to be ripe and in the best condition for use at
the time it contains the greatest number of living bacteria. It
has been found by experiment that this is at the time the milk
curdles at ordinary temperature, or when the acidity is about
0.6-0.7 per cent. If the acidity is allowed to increase to 0.8 or
0.9 per cent, the number of bacteria will be less and a larger
amount of the starter must be used in order to ripen a definite
amount of cream in the desired time. The use of an overripe starter
may also have an injurious effect on the flavor.
[Illustration: Fig. 31.--Bottle for Mother Starters.
A milk bottle with a tumbler for a cover and a spoon for inoculating
the other bottles enables the butter maker to propagate the starters
without contamination.]
The ripened starter should be perfectly homogeneous, showing no
bubbles of gas or free whey; the odor should be agreeable and the
acid taste mild; on shaking, the curd should break up into a smooth,
creamy liquid free from lumps. This is especially important in the
starter that is to be added to the cream, since otherwise the
starter cannot be uniformly mixed with it and white specks of
curdled casein will be noted in the butter.
[Illustration: Fig. 32.--An Incubating Chamber for Starters.
The inner compartment will hold a pail of water and the bottles for
the mother starters. The temperature can be kept at any desired
point by the use of warm or cold water. The four-inch space between
the walls is filled with hay or mineral wool.]
The firmness of the curd is not so dependent on the amount of acid
formed as upon other factors. If the curd shrinks to any extent and
the whey is expressed, it is certain to produce a starter that will
contain lumps that cannot be broken up. With a pure culture of
lactic bacteria, there is little difficulty in this regard, but as
soon as gas-forming bacteria are introduced, trouble is likely to
result.
In the propagation of starters, it is always to be remembered that
the bacteria, although invisible to the eye, are living things, and
unless conditions are favorable in every particular, it is
impossible to keep them in a healthy condition, so that growth in
the cream is rapid, producing the acid demanded for churning, and
imparting to the butter the desired flavor, both as to degree and
kind. No part of the daily routine of the butter maker should be
performed with more care than the preparation of the starters, both
the mother starters, and the larger one for addition to the cream.
The latter can best be made in one of the many forms of starter cans
now on the market, since by their use, the maker can heat and cool
the milk with little trouble, and can maintain the starter at any
desired temperature. Better starters cannot be made in them than by
the use of simple and improvised apparatus, but better results can
be obtained with the same expenditure of time and labor.
In the handling of the large starter, care should be used not to
overripen, since the larger quantity is more likely to "whey off"
than is the smaller starter. Skim milk rather than whole should be
used for this. It should be selected with care and heated to 200 deg. F.
for thirty minutes. When it is impossible to secure fresh milk for
starter making purposes, either condensed skim milk or milk powder
may be used. The condensed milk is diluted with water until its
volume is about the same as the milk before concentration; the
mixture is then treated the same as fresh milk, being heated and
cooled before inoculation. In the case of milk powder, one part of
the powder is added to ten or twelve parts of water, allowed to
dissolve as far as possible, and the mixture heated and cooled.
Either of these liquids will give satisfactory starters; the cost
however is high, and in most places milk can be obtained more
cheaply. The inoculation and the temperature should be so
controlled, as to ripen the starter at the time it is to be needed.
These conditions must be determined by the maker for himself. It
should be remembered that the bacteria grow much more rapidly, as
the temperature is increased; and hence, the amount of inoculation
is dependent on the temperature at which the starter is to be kept.
When the starter is propagated under practical conditions, it sooner
or later deteriorates, either in acid production, or in flavor, and
a new pure culture must be procured from the manufacturer. It is
impossible to give a hard and fast rule as to the length of time a
starter can be kept in good condition. It will depend on how well
the maker satisfies the conditions necessary for maintaining its
purity and strength. The use of imperfectly sterilized milk, or
dirty utensils soon contaminates it; overripening is likely to
injure the flavor. One of the most frequent troubles encountered is
the appearance of a slimy or ropy condition in the starter, although
the acidity developed may be normal and the flavor desirable. It has
been found that this condition is not necessarily due to
contamination, as was considered true in the past, but rather to
some change in the lactic bacteria themselves. If the propagation is
continued, the slimy condition will often disappear.
=Starters in "process" butter and oleomargarine.= The advance which
has recently been made in the science and practice of cream ripening
and butter production is utilized most effectively in the treatment
of cream in the renovating process. Old, soured, and stale cream
is reduced in acidity by the addition of lime. The cream is then
pasteurized and aerated to expel the odors as much as possible. A
large amount of starter is then added and the cream immediately
churned. Under these conditions, the bad flavors are materially
reduced in intensity, and desirable flavors absorbed by the fat from
the selected starter used. It is thus possible to produce butter of
good quality from cream that would at first be regarded as quite
unsuitable for butter production.
In the manufacture of oleomargarine the same principle is utilized.
The butter aroma and flavor is imparted to the neutral oils and
tasteless fats by mixing the same with a properly prepared starter.
Renovated or process butter is given a desirable flavor in the same
way.
=Wash water.= It has been found that the purity of the water used in
washing the granular butter has a marked influence on the keeping
quality. If the water is from a shallow well into which surface
water finds its way, it is certain to contain large numbers of those
types of bacteria that are found in the soil, while if it comes from
a deep well that is properly protected from surface contamination,
the bacterial content of the water will be low and no injurious
effect on the butter will be noted. When it is impossible to obtain
pure water for washing purposes, a proper supply may be secured by
sterilizing the water. The most convenient way of heating the water
is by the direct injection of steam. It is necessary to use that
coming directly from the boilers and not the exhaust from the
engine, since the latter is likely to contain small amounts of oil
that will impart to the butter an objectionable flavor. After
cooling, the water is ready for use. It has been shown that the
cost of treating an impure water is more than covered by the
increased returns from the product.
A pure and healthful water supply should be one of the essential
things of every dairy, creamery, and cheese factory, not only for
the sake of the quality of the product, but also to avoid
contamination of products with disease-producing bacteria.
=Bacteria in butter.= The germ content of butter will depend on the
type of cream. Sweet-cream butter contains but few bacteria. In
sour-cream butter the content in bacteria will be greatly increased,
especially as to lactic organisms. Often, it may amount to several
millions of organisms per gram. The germ content of butter is said
to be greater on the outside of a package than within the mass, due
doubtless to the free access of air, thus favoring the growth of the
aerobic forms.
The composition of normal butter does not favor the growth of the
majority of kinds of bacteria that are contained in it. The washing
process removes much of the material suitable as food for the
bacteria, such as sugar and albumen. If considerable butter milk is
left in the butter, the growth of bacteria will be quite rapid, at
first, but does not continue for any considerable length of time.
The addition of salt also tends to restrain the growth of most kinds
of bacteria.
Butter is at its best when it is perfectly fresh. Deterioration
begins within a short time and the rapidity with which the changes
go on is dependent on the temperature at which the butter is stored.
The temperature of the butter rooms in the large cold storage plants
is kept below 0 deg. F. The butter in such rooms will deteriorate very
slowly, but on removal from the cold rooms and in storage at
ordinary temperatures deterioration goes on more rapidly than would
have been the case when the butter was fresh. At the temperature of
an ordinary refrigerator the changes go on much more rapidly. This
fact has often been looked on as indicating that the factors causing
the changes are biological ones. The influence of temperature in
accelerating the changes would be the same if no biological factor
were active.
That biological factors are of importance is indicated by the fact
that the keeping quality of the product is profoundly affected by
the quality of the cream. Butter made from sweet, fresh cream, that
has been thoroughly pasteurized, has the best keeping quality, while
butter made from such cream, but not pasteurized, has the poorest
keeping quality, especially when no salt is added. Every process by
which the desirable lactic bacteria are increased in proportion to
other kinds has a marked effect in enhancing the keeping quality of
the butter. Thus, the use of pure cultures in raw cream, and
pasteurization together with the pure cultures, have a marked
beneficial effect.
The addition of preservatives exerts an effect on keeping quality.
Borax is the chemical most frequently employed for this purpose. Its
use is allowed in Australia and New Zealand in butter that is
shipped to England, but the use of all preservatives is forbidden in
the United States.
The size of the package also has an effect on the keeping quality;
the smaller the package, the greater is the surface exposed to the
air and the more rapidly the butter deteriorates. Butter used in the
United States Navy is packed in hermetically sealed cans so as to
exclude the air as far as possible.
From the fact that any condition which restrains or inhibits the
growth of micro-organisms has a tendency to improve the keeping
quality of butter, it would appear that the detrimental changes in
the quality of butter are due to biological causes. The most common
defect known is that usually referred to as rancidity. There are,
however, different types of changes that are probably included under
this head and it is very probable that different causes are
operative in their production. True rancidity is probably due to
biological causes; the so-called tallowy change, in which the butter
acquires the odor of tallow is probably due to the combined action
of light and air on the fat.
=Bacterial defects in butter.= There are a number of defects in butter
that are positively known to be due to the growth of bacteria in the
milk or cream, or in the butter itself. The lack of flavor is looked
upon as a defect in the case of ripened-cream butter. It may be due
to insufficient ripening of the cream, or to the lack of
acid-forming bacteria that produce the desirable flavor-forming
compounds. Not all acid-forming bacteria are able to produce
favorable, flavor-giving compounds; hence, sour cream butter may
sometimes be deficient in flavor by reason of this fact.
=Putrid butter.= This specific butter trouble has been observed in
Denmark, where it was first studied by Jensen. Butter affected by it
rapidly acquires a peculiar putrid odor that ruins it for table use.
Sometimes this flavor may be developed in the cream previous to
churning. It may be caused by a number of bacteria.
=Turnip flavored butter.= Butter sometimes acquires a flavor
resembling turnips. This trouble may be due to the feeding of such
roots, the aromatic substances peculiar to them being absorbed
directly by the milk and thus transferred to the butter. Weigmann
traced a similar flavor to certain bacteria that entered the milk
from barn filth.
=Cowy odor in butter.= There is sometimes to be noted an odor in
butter as in milk that resembles that of the cow stable. Usually
this defect has been ascribed to the absorption of these odors
directly by the milk. Organisms have also been described that impart
to the butter a very similar odor. Bitter butter may be due to the
feed that is consumed by the cow, or it may be due to those forms of
bacteria that produce a bitter fermentation of the milk.
=Other abnormal flavors.= Among the numerous abnormal flavors that
have been noted in butter is one of quite frequent appearance, the
so called "fishy" flavor. It is now believed by many that this
flavor is due to the presence of small amounts of iron or copper
salts that have been introduced into the milk from utensils from
which the protective coating of tin has been worn. If the milk or
cream stored in such utensils develops any marked degree of acidity,
the acid will dissolve a small amount of the iron or copper. The
fishy flavor has not been found in sweet-cream butter as would be
expected from the above explanation. In fresh butter a metallic
taste is sometimes present. It is believed by some that on storage
this flavor changes to the fishy flavor.
All utensils used for the storage of milk and cream should be kept
in good condition so as to prevent the acid milk or cream from
coming in contact with iron or copper.
[Illustration: Fig. 33.--Moldy Butter.
The mold grows on the paper in which the butter is wrapped rather
than on the butter. The print on the left was wrapped in the same
paper as the print on the right except that the parchment cover had
been steamed for a few moments.]
=Moldy butter.= A defect that causes a great amount of loss is the
development of mold on the surface of the butter, either in tubs
or in prints. This trouble is easily prevented. Butter is not well
suited to the growth of mold, but the paper used for lining the
tubs, or wrapping the prints is an excellent medium for mold growth.
The wood of the tub also furnishes ample food for this type of life,
especially where the wood contains any sap. One other essential
condition for mold growth is a supply of oxygen. The mold spores are
widely disseminated, and are always to be found on the butter tubs
and on the paper. The number is not likely to be sufficient to cause
trouble unless the tubs and paper have been kept under such
conditions, as to allow growth to take place on them before use.
During damp, hot weather, the amount of moisture absorbed by these
materials is often sufficient to allow molds to grow on them. This
trouble can be prevented by the storage of tubs and paper in a clean
dry place, or by a disinfecting treatment which will destroy the
mold spores. The most successful method of treatment of tubs is to
apply paraffin to the inner surface, which can be easily done by the
use of some one of the various machines now on the market. The
thin layer of paraffin excludes the moisture from the wood, and also
prevents the mold from obtaining a supply of oxygen for its growth.
The tubs may be steamed, treated with hot water, or filled with a
dilute solution of formaldehyde, and allowed to stand overnight.
Soaking in brine as is usually done in the creameries is of some
effect, but will not completely kill mold spores.
[Illustration: Fig. 34.--Moldy Butter.
The butter was placed in a paraffined tub, but the paper was not
treated so as to destroy the mold spores thereon.]
Butter may mold where the tubs have been thoroughly treated, because
of the mold spores on the paper used for the lining. One of the
black molds is able to thrive on parchment paper whenever the air is
damp. In the past but little attention has been paid to the paper as
a source of trouble. It is certain that it is often at fault, and
that as much attention should be paid to the paper as to the tub. A
most efficient way of treating paper, either for tub liners or print
wrappers is to place same in boiling water for a few minutes.