Bulletin No. 585

4

October, 1930

v,

'^Çeftéva, N. Y.

STRAINING MILK ON THE FARM

A. C. DAHLBERG

PUBLISHED BY THE STATION

UNDER AUTHORITY OF CORNELL UNIVERSITY

CORNELL UNIVERSITY

NEW YORK STATE AGRICULTURAL EXPERIMENT

STATION, GENEVA, N. Y.

STATION STAFF

Ulysses P. Hedrick, Sc.D., Director.

Robert S. Breed, Ph.D.,

George J. Hucker, Ph.D.,

Chiefs in Research (Bacteriology).

Harold J. Conn, Ph.D.,

Chief in Research (Soil Bacteriology).

Carl S. Pederson, Ph.D.,

Associate in Research (Bacteriology).

P. Arne Hansen, B.S.,

Assistant in Research (Bacteriology).

Fred C. Stewart, M.S.,

Mancel T. Munn, M.S.,

Chiefs in Research (Botany).

Mary E. Woodbridge, M.S.,

Olive M. Sipple, B.S.,

Assistants in Research (Botany).

Walter O. Gloyer, M.A.,

W. Howard Rankin, Ph.D.,

Edward E. Clayton, Ph.D.,(Riverhead),

James G. Horsfall, Ph.D.,

James M. Hamilton, Ph.D.,

Associates in Research

(Plant Pathology).

Dwight C. Carpenter, Ph.D.,

Arthur W. Clark, B.S.,

Leon R. Streeter, M.S.,

Chiefs in Research (Chemistry).

Morgan P. Sweeney, A.M.,

Edmund L. Green, M.S.,

Z. I. Kertesz, Ph.D.,

Associates in Research (Chemistry).

William F. Walsh, B.S.,

Frank Kokoski, B.S.,

Floyd E. Lovelace, A.B.,

George W. Pearce, M.S.,

John J. Kucera, Ph.D.,

Assistants in Research (Chemistry).

Arthur C. Dahlberg, Ph.D.,

Chief in Research (Dairying).

J. Courtenay Hening, M.S.,

Associate in Research (Dairying).

Julius C. Marquardt, M.S.,

Assistant in Research (Dairying).

Herbert L. Durham,

Dairy Technologist.

Percival J. Parrott, M.A.,

Vice-Director ; Chief in Research

(Entomology).

Hugh Glasgow, Ph.D.,

Paul J. Chapman, Ph.D.,

Chiefs in Research (Entomology).

Fred Z. Hartzell, M.A.,

Hugh C. Huckett, Ph.D. (Riverhead),

Frederick G. Mundinger, M.S.

(Poughkeepsie),

S. WlLLARD H ARM AN, M.S.,

Derrill M. Daniel, M.S.,

G. E. R. Hervey, Ph.D.,

Associates in Research (Entomology).

Foster L. Gambrell, Ph.D.,

Assistant in Research (Entomology).

Richard Wellington, M.S.,

Harold B. Tukey, M.S.,

Reginald C. Collison, M.S.,

Chiefs in Research (Pomology).

Fred E. Gladwin, B.S. (Fredonia),

George H. Howe, B.S.,

Glen P. Van Eselttne, A.B.,

Lester C. Anderson, B.S. (Hudson),

George L. Slate, M.S.,

Bernard R. Nebel, Ph.D.,

Associates in Research (Pomology).

Olav Einset, M.S.,

Lewis M. Van Alstyne, B.S.,

Karl Brase,

James D. Harlan, B.S.,

Assistants in Research (Pomology).

Charles B. Sayre, M.S.,

Chief in Research (Vegetable Crops).

William T. Tapley, M.S.,

Associate in Research

(Vegetable Crops).

Leslie R. Hawthorn, M.S.,

Parks V. Traphagen,

Assistants in Research

(Vegetable Crops).

Patrick H. Corcoran, Agriculturist.

James D. Luckett, M.S., Editor.

Hermann O. Jahn, Florist.

Marjorie B. Rogers, Librarian.

James S. Lawson, Phm.B.,

Museum Preparat or.

Bulletin No. 585

STRAINING MILK ON THE FARM

A. C. DAHLBERG1

ABSTRACT

Milk should be produced under careful sanitary conditions, but

nevertheless it needs straining. Milk is strained to remove most

of the visible sediment to improve its appearance. Filtration

refers to the complete removal of all visible sediment. It is not

essential and it is rather difficult to remove all visible sediment

from milk on the farm. Straining is ample as milk must be

filtered or clarified at the milk plant.

Single-service cotton or flannel discs or squares are generally

employed. Cloth is more satisfactory due to greater capacity

even tho cotton removes more sediment. Most strainers using

cotton handle so little milk that their value is questionable. A

suitable strainer using cotton, embodying most of the principles

discussed in this bulletin, and which has reasonably good capacity

is illustrated on page 9. Cotton is recommended for milk sold

raw which cannot be filtered or clarified at the milk plant and for

those dairies where exceptionally good sediments are desired and

small capacity is not important.

The capacity of a strainer decreases with low temperatures and

with high fat content of the milk.

Cloths or cotton discs or squares clog with small amounts of

butterfat even when very clean milk is being strained.

Photographs with legends are given on pages 9, 1 0, and 1 3

showing strainers which illustrate certain desirable features when

used with either cloth or cotton.

The features to be considered in selecting and using a single-

service milk strainer are summarized on pages 20, 21, and 22.

^he author is indebted to Dr. John Drew of the Dairymen's League Co-

operative Association for helpful suggestions and cooperation during the course of

this study. The author is also indebted to manufacturers of strainers and of cotton

pads and cloths for their cooperation in furnishing samples and in constructing

certain suggested features in their equipment for experimental studies.

INTRODUCTION

The amount of foreign material that finds its way into milk ought

to be kept at a minimum even tho it is entirely feasible in the milk

plant to remove almost completely all insoluble, visible material. Pub-

lic health officials and milk sanitarians are correctly emphasizing that

milk should be produced as pure as possible in its original condition even

tho it is later subjected to certain treatments to insure its safe con-

sumption.

The presence of foreign material in milk is particularly undesirable

since it indicates that its production has not been surrounded with

suitable sanitary conditions.

It is doubtless true that extraneous material which finds its way into

milk may not usually be particularly injurious to health, but consumers

want .and ought to have clean milk. Sediment often introduces foreign

flavors and odors, and it may slightly affect the bacterial content of milk

even tho it usually does not contain disease-producing organisms.

Numerous investigations have clearly demonstrated that sediment found

in milk has usually not been an important factor in affecting the bac-

terial count of the milk.

So far as any experimental evidence is concerned, the removal of

foreign sediment by suitable methods of straining or filtering has little

effect upon the healthfulness of the milk. Contaminations produced by

the extraneous material are effected to a considerable degree as soon as

this material comes in contact with the milk so that the problem of

straining is largely concerned with the marketability of milk. The

whiteness of milk makes it an ideal medium in which extraneous

material can be readily seen and the presence of visible sediment

materially affects its market value.

Even tho milk is produced with the utmost of care, it is very desirable

that it should be strained immediately after it is produced as an added

precaution in its sanitary handling. This has been recognized for many

years and most old literature on this subject makes mention of the

desirability of straining milk.

Rham,2 in 1845, stated that milk should be strained immediately

following production thru a fine metal or cloth sieve.

In his book on Dairy Farming published in 1856, Ruricola::! states

2Rham, W. L. Dictionary of the Farm. London: Charles Knight and Co.

1845.

3Ruricola. Dairy Farming. London: John Edward Taylor. 1856. (See

page 141.)

that milk "ought to be passed thru a wooden bowl ß,t the bottom of

which there should be a hole of about two inches in diameter, covered

with a fine wire gauze made of brass or silver; the latter is of course

preferable as being equally durable and less likely to corrode."

Just 50 years ago Sheldon4 described a wire strainer with a hundred

meshes per inch which would remove visible sediment from milk. It is

interesting to observe that his conclusions have, in the main, been veri-

fied at this Station during the last year.

A large variety of materials, such as sponges, sand, pyrites, and char-

coal, have been tried experimentally for milk straining purposes in milk

plants. On dairy farms the straining devices have been wire gauze,

cloth, and cotton pads. In many sections of the country the wire

strainer is extensively used, while in other places, particularly in certain

sections producing market milk, the use of the wire strainer has been

barred thru rulings of public health officials and milk sanitarians. At

the present, time thru the northeastern United States single-service cloth

or cotton pad strainers are almost universally recommended.

A detailed review of the literature on the subject of milk straining

would be too lengthy for this popular presentation.

THE PROBLEM OF SINGLE-SERVICE STRAINERS

Lack of sanitary precautions on the part of dairy farmers in cleaning

and sterilizing wire mesh and cloth strainers which would be used over

and over again led to regulations requiring the use of single-service

cloth or cotton strainers. The introduction of these strainers was very

rapid and few manufacturers of strainers or straining materials had an

opportunity to consider the problem sufficiently to give dairy farmers

an entirely suitable product.

The problem was studied at this Station because of the necessity of

securing some satisfactory straining device. In 1924,5 the first publica-

tion from this Station on the removal of sediment from milk dealt exclu-

sively with the problem from a milk plant standpoint. Since that time

a large number of straining devices have been collected for use in

straining the Station's milk supply which consists of the product of a

herd of 26 Jersey cows. For the past five years almost every straining

device on the market has been collected and tried experimentally, not

4Sheldon, J. P. Dairy farming. London: Cassell, Petter, Galpin and Co

1880. (See page 447.)

5Dahlberg, A. C, and Marquardt, J. C. Filtration and clarification of milk.

New York State Agr. Exp. Sta. Tech. Bui. No. 104. 1924.

because they were unsatisfactory from the standpoint of removing the

sediment from milk, but because they failed to give satisfactory ca-

pacity. In most instances the cotton cloths and cotton pads supplied

with the strainer would clog prior to straining one 10-gallon can of milk

or thin spots would develop in the cotton.

The question immediately arose concerning what constituted satis-

factory straining from the standpoint of the dairy farmer. How much

milk should be poured thru a single cloth or cotton? How completely

should the straining medium remove visible sediment?

At the present time there is much division of opinion concerning

standards for judging a milk strainer. Some manufacturers of cloth

and cotton for straining contend that only one 10-gallon can of

milk should be passed thru one cotton pad or cloth. The most efficient

results are said to be secured by the continual changing of the straining

material. Thus it is evident that the cost of straining is materially in-

creased. Quite aside from the question of removing the sediment from

milk is the problem of sanitary conditions involved in this procedure.

A dairy farmer milking cows seldom has the time or the conveniences

to change cotton pads or cloths in a wet strainer without introducing

contamination from the hands which may carry disease organisms.

Contamination of this type, altho invisible, is far worse than the

presence of visible sediment in milk.

It seems evident that a satisfactory strainer must permit the flow of

milk with sufficient speed so that it will not interfere with the rate at

which one man can milk cows by machine. The maximum capacity of

the strainer ought to be sufficient to handle a complete milking on an.

average good sized dairy farm. This would mean that the cotton pad or

cloth ought to strain not less than three 10-gallon cans of milk.

If the strainer has sufficient speed, then it may be considered from the

viewpoint of the efficiency with which sediment is removed. Speed in

straining is given first consideration because it is essential from the

dairyman's standpoint that the straining of milk should not interfere

with routine work. When a strainer has sufficient speed it cannot do<

the most perfect filtering, but it can do reasonably satisfactory straining.

There is need for a brief discussion of the two terms, straining and

filtering, commonly used in the production of market milk. When milk

is strained most of the visible sediment is removed from it. It may be

possible to find traces of foreign material on the sediment disc or in the

bottom of the milk bottle after it has stood undisturbed for 24 hours

even tho milk, produced under good sanitary conditions, has been.

7

satisfactorily strained. The word filtration has been applied to dairy

farm practices in the past few years, but the accuracy of its usage is

questionable. Most thoro filtration would remove all fat and proteins,

much of the ash, and the filtered milk would be whey. The least that

can be expected of filtration is the complete removal of all visible

sediment from milk. It is doubtful that filtering can ever be done on

the farm because dairy farm operations do not lend themselves to milk

filtering. If milk is to be filtered it is essential that it must be main-

tained at a temperature of not less than 90° F and some pressure must

be exerted upon the filtering medium by the milk. Colder milk can

be filtered by greatly increased pressure. In the winter months milk is

below this temperature and there is seldom sufficient head pressure in

the strainer to force the milk thru a fine filtering device.

Irrespective of the thoroness with which milk is strained on the farm,

it is essential that it must be filtered or clarified in the milk plant. Such

being the case there is no necessity of filtering milk on the farm. Fur-

thermore, if milk is well filtered on the farm it is impossible for the

milk inspector to examine a given lot of milk to determine the sanitary

conditions surrounding its production. The presence of a portion of

the sediment that has found its way into milk serves as a guide to the

milk inspector in locating unsanitary conditions.

METAL EQUIPMENT FOR STRAINERS

The number of straining funnels now on the market is too large for

any individual dairyman to ever hope to try more than a small part of

them. This fact is illustrated in Fig. 1 which shows all of the metal

straining equipment used in the last series of tests. There are 22 dif-

ferent funnels illustrated, and they represent but part of those used

during the course of the experiments.

Well reinforced and heavily tinned iron is generally used in con-

structing strainers. Some strainers have been made of aluminum, but

this metal in thin sheets is somewhat soft and tends to dent very badly

according to experiences in straining the Station's milk supply. Some

strainers are too lightly constructed. The funnel need not be of ex-

cessive capacity if the milk passes thru it with sufficient rapidity. The

usual capacity of 12 to 16 quarts is ample. It is desirable that the

strainer should be seamless and free from indentations or irregularities

of any sort on the inside, illustrated in Fig. 2. A number of the strain-

ing devices are so constructed that they are rather difficult to wash.

This applies particularly to funnels with irregular internal surfaces,

8

'Sitó

Fig. 1.—These Strainers are all Different and Were Used in the Last

Series of Tests Made in the Winter of 1929-30.

with seams, with close woven wire grids, and discs that have openings

that are rather difficult to wash, particularly when the disc is soldered

into the bottom or is an integral part of the funnel. The most simply

constructed funnel and equipment that operates well is the best.

Every straining funnel ought to be so equipped that the dairyman

can use it with cotton or with cloth because there is a marked difference

in preference for cloth or cotton in various sections of the country.

Strainers ought to be constructed to give a maximum straining sur-

face for the can in which the strainer is used. Thruout the Middle

West the predominating 10-gallon can has a neck 6*4 inches in

diameter. For a can with a neck of this size a strainer with an outlet

or foot that is 5^4 inches overall represents the maximum size that can

be satisfactorily employed. Thru the North Atlantic states the pre-

dominating 10-gallon can has a neck that is l1/^ inches in diameter.

B

D

Fig. 2.—A Strainer that Illustrates Certain Principles in Design.

The funnel B (inside View) is absolutely smooth inside and has no seam. The

clamp A is used only when cloth is attached to the outside of the funnel. The

wire grid D is the under support to hold cotton from breaking or washing and

to hold cloth from stretching. The wires in the grid are not interwoven but

one row lays on the other and are electrically welded and tinned. The conical

perforated disc C fits so tightly into the foot of the funnel B that it will hold

a cloth in place without the use of the wire grid D and it prevents leakage of

milk around the disc. The disc is convex so that there is a clearance of from

Ys to % inch between the disc and wire grid to give room for expansion of

the cotton when wet.

For a can of this type it is possible to use a strainer that is about 6%

inches in diameter. This extra size of the foot greatly increases the

capacity of the strainer.

The equipment which goes with the straining funnels is exceedingly

numerous and varied. It is fortunate that certain principles can be

stated that hold for all types of straining equipment.

Cotton pads must be placed upon some support and the stream of

milk cannot be poured directly upon the cotton or the pad will become

irregular in thickness. It is also essential that the cotton must not be

packed so that a conical or raised upper disc must be employed. The

equipment must fit together well to prevent milk from flowing around

the cotton. These points are illustrated in Figs. 2 and 3.

Calculations showing the influence of the diameter of the foot and

10

*.

Fig. 3.—The Strainer Shown in Fig. 2 Being Put Together with Cotton

Which is Gauze Faced on One Side.

It is put together upside down. The gauze and perforated disc are now on the

underside of the cotton. Cloth can be used in place of cotton and the wire

grid may be omitted with cloth as the disc fits snugly in the funnel.

various devices for supporting the cotton are shown in Table 1. The

first three strainers fit the small-necked can and the last three fit the

large-necked can. These calculations were made to explain the marked

variations which were experimentally encountered in the capacity of

various strainers. A study of the table will show that a disc for sup-

porting the cotton perforated with large holes gives the smallest

capacity. A perforated disc with a large number of small holes gives

approximately double the capacity that is present in the large-holed

t

11

Table 1.—The Influence of Size of the Strainer Outlet and the Support

for the Cotton on the Capacity of the Strainer.

Foot diameter

Holes

Area in square

Strainer

IN INCHES

Type of cotton

support

inches

no.

Size

Strain-

Inside

Outside

in

inches

Number

Total

foot

ing

(holes)

1

434

S

Bottom perforated

Va

98

17.72

4.07

2

5

534

Perforated disc

A

302

19.64

8.34

3

5

534

Wire grid

—

19.64

18.11

4

S'A

Bottom perforated

4

181

23.76

7.52

5

Sil

àVs

Perforated disc

A

446

26.53

12.32

6

51t

Wire grid

654t

—

26.53

26.48

*Inside dimensions of ring holding wires. Total area 20.63 square inches. Total

length of wires 50^2 inches, diameter of each wire 1/20 inch. Wires placed 8 strands to 3

inches to make 5/16 inch square openings to support cotton. Area of wire 2.52 square

inches.

tlnside dimensions of ring holding wires. Total area 30.68 square inches. Total

length of wires 84 inches, diameter of each wire 1/20 inch. Wires placed 8 strands to 3

inches to make 5/16 inch square openings to support cotton. Area of wire 4.2 square inches.

disc. When the perforated disc is eliminated and a wire grid is used to

support the cotton, then the capacity of the strainer is approximately

double that which is given by the small-holed perforated disc. These

calculations agree very closely with those experimentally obtained in

straining milk. It is interesting to note that the perforated disc in the

strainer with the large foot does not give as much capacity as the small

strainer with the wire grid. The maximum capacity is of course given

by the strainer which has the foot of largest diameter and in which the

cotton is supported by a wire grid.

Some objection may be raised against the wire grid, Figs. 2 and 3,

on the basis that it is difficult to wash. It is true that it is more difficult

to wash than a flat surface, but it can be readily cleaned. No piece of

dairy equipment will remain in a sanitary condition without proper

washing and sterilizing. It is difficult to wash the metal around the

openings in a perforated disc, yet few milk inspectors have objected to

this equipment. The Drew wire grid does not have interwoven wire so

that the ease of washing is aided. Experience at this Station indicates

that this wire grid is as easily washed as the perforated disc.

The conical disc which is placed on top of the cotton should be bent

sufficiently so that it will never press upon the cotton even after it be-

comes soaked with milk. A flat perforated disc can be used if it is held

about Y%to%. inch above the wire grid. Experiments have shown that

there is little merit in the various methods of perforating the upper

conical disc to force milk to flow upon the cotton from different angles.

12

When the disc was perforated with 100 to 125 holes which were 3/16 of

an inch in diameter, the speed of the strainer was just as rapid as with

any other method of perforating the disc. Holes of this type permit the

use of a disc which is strong and easily washed.

Irrespective of the type of equipment employed, cotton without rein-

forcing, which is so universally used, will wash badly. It is essential

to the securing of uniformly good results that a thin gauze should pro-

tect the cotton on the top where milk strikes it. Single or double cloth

faced cotton should be used. It is true that plain cotton does give more

capacity than gauze-faced pads and that it is less expensive. However,

the formation of thin areas in the cotton by the washing of the milk

gives uncertain straining efficiency so that the best results are not always

secured. It is to be hoped that a strainer will eventually be devised in

which plain cotton can be used with uniform results.

The equipment which gives best satisfaction for supporting the cotton

pad, Fig. 3, also gives the maximum capacity with the cloth when placed

inside the strainer funnel and it can be satisfactorily used when more

milk needs to be strained than will pass thru cotton. A smaller cloth

is satisfactory with the inside equipment, thus slightly reducing the cost

of cloths as compared with the outside attachment, if one cloth is suf-

ficient to strain the milk.

The cloth is more rigid than the cotton and can stand pouring of milk

directly upon it and it needs no support underneath. Numerous tests

have been made on cloths with and without supports. These tests have

invariably shown that the capacity of the cloth is almost doubled when

there is no supporting grid. This means that the average thin outing

flannel generally employed for straining milk will handle about three

cans of milk in the winter months when it is used inside the straining

funnel with a supporting wire grid, but it will strain about five cans of

milk if it is attached to the outside of the strainer, as shown in Fig. 4.

The increased capacity is much greater than the increase in the cost of

the cloth due to the extra size required to make the outside attachment.

It is also interesting to note that this same flannel when supported on

the inside of the strainer with a perforated disc, instead of the wire grid,

will strain only one, or occasionally two, cans of milk without clogging.

These figures were secured experimentally, but the quantities will vary

tremendously depending primarily upon the temperature of the milk at

the time of straining.

Perhaps the most satisfactory outside clamp for holding the cloth is

a plain band drawn tight to the funnel by an eccentric clamp, Fig. 4,

13

Fig. 4.—The Use of Flannel Attached to the Outside.

The band is pushed down over the cloth and the clamp is then turned snugly

against the strainer to tighten the band. The reinforcing on the extreme outer

edge of strainer, shown in Fig. 3, holds the cloth and band from slipping

off. This clamp comes in contact with milk only if the cans are overfilled.

the cloth and clamp being held in place by the reinforcing at the foot of

the strainer. If reasonable care is used in placing the cloth and clamp

on the strainer there is no danger that they will ever slide off. The

eccentric clamp shown in Fig. 4 is not very sanitary, due to difficulty

in washing the holes in which the crooked wire is held, but it comes in

contact with milk only when the can is overfilled. Cloths can be held

14

satisfactorily by inside tight fitting equipment, but for the greatest

capacity there should be no under support.

SINGLE-SERVICE CLOTH AND COTTON

Most dairy farmers in the sections using single-service straining

media employ cotton pads. This is probably due to the fear of milk

inspectors and milk plant operators that cloth may be used several times

before being discarded and to sales pressure by cotton manufacturers

rather than to the choice of dairymen. Repeated use of cloth can be

avoided by milk plants selling cloths to dairymen in regular amounts,

thereby avoiding any reason for not discarding the cloth after each

milking. Difficulty with capacity of cotton pads is almost universal

since most strainers using cotton seldom strain more than one can of

milk and often clog before 40 or 50 pounds of milk have been strained.

Observations on dairy farms support the belief that when ample ca-

pacity is secured with cotton it is due either to thin areas being formed

by washing the cotton with the milk or the milk flows around the

cotton due to poor adjustment of the cotton to the straining funnel.

In other words, capacity is generally secured by failure of all of the

milk to pass uniformly thru the cotton.

During the course of these experiments scores of cotton pads of

various types have been tried and in no instance up to 1930 has any

cotton pad ever been secured which, when placed in the usual strainer,

would strain one 10-gallon can of Jersey milk during the winter months.

Under these conditions it is practically impossible to state other than

that the use of cotton pads has generally been very unsatisfactory due

to lack of capacity.

In recent months the capacity of cotton pads has been increased by

improved manufacturing methods. These newer cotton pads can be

used in the new large foot strainer described in this bulletin to strain

one or two cans of milk in the winter months and about three cans of

milk in the summer. Since cotton is most efficient in removing sediment,

it can be satisfactorily used on small dairies without changing the cotton

during milking. The larger dairies ought to use two or three funnels to

make it unnecessary to change the cotton during milking. Cotton has

a special place in grade A dairies, particularly those selling grade A raw

milk which is not filtered or clarified at a milk plant.

The simplest and easiest manner of increasing the capacity of cotton

pads would be to decrease their thickness. They are now much thicker

than necessary for satisfactory straining. Most cotton pads of 6j4-inch

IS

diameter weigh from 170 to 220 grams (about 6 to 8 ounces) per 100.

If the amount of cotton was reduced to 120 to 150 grams per 100 a

much more satisfactory and serviceable straining medium would be

secured. Manufacturers of cotton discs or squares have experienced

difficulty in spreading cotton so thinly without leaving very thin areas.

Due to methods of manufacture, there may be differences in the capacity

of cotton pads of uniform weight.

Whenever farmers encounter difficulty with the capacity of cotton

pads they are generally advised that the failure of the cotton pad to

strain the milk is due to the dirt in their milk. There is little justifica-

tion for this statement except in very extreme cases. Cotton pads

generally clog due to the retention of the large clusters of fat globules

which are present in the milk under most circumstances, particularly

when cold. The cotton pads used for straining Jersey milk during the

winter months usually contain a milk-cream mixture which tests from

8.0 to 12.0 per cent of fat. The fat content of the fluid remaining in the

strainer cotton is easily secured by placing the cotton in a closed glass

container, heating to 130 or 140°F and squeezing out the liquid by

hand. It can then be tested for fat in the usual way. When Holstein

milk is strained the fat content of the milk remaining in the cotton

varies from 4.0 to 8.0 per cent, depending primarily upon the tempera-

ture and amount of milk strained. Ordinarily, the colder the tempera-

ture the richer the fat content of the milk remaining in the cotton. In

some experiments the fat content of the fluid remaining in the cotton

after straining skimmilk testing 0.01 per cent by the Babcock method

was found to be between 2.0 and 3.0 per cent. These results clearly in-

dicate that cotton pads clog and fail to give ample capacity due to the

retention of butter fat.

Further evidence supports this contention. If a cotton pad clogged

with fat is cleaned by pouring hot water thru it, the capacity of the

cotton will be restored to approximately one-half of that which it

originally had. These results can be secured even when precautions are

taken to avoid jarring the cotton or washing thin spots in it with water.

The total weight of fat lost in each cotton pad is small because of the

small amount of liquid which it holds. The fat in each cotton after

clogging is about 3 grams or 0.1 of an ounce. When the cotton pads

are discarded before they become clogged or when cloths are used, the

fat losses are only one-fourth or one-third those just given. These facts

emphasize the importance of ample capacity to save butterfat as well

as the cost of extra cottons or cloths.

16

The rapidity with which a cotton clogs with fat is illustrated by

Fig. 5. Jersey milk free from visible sediment was poured continuously

thru the cotton at 90°. The amount of milk strained each minute was

recorded. The cotton strained the first 10-gallon can of milk in less

than 2 minutes, but it could not finish another 10 gallons of milk.

Flannel cloths attached to the outside of the funnel have been found

to be so satisfactory that they have been employed regularly at this

institution for nearly three years. There are a considerable number of

thin bleached outing flannel cloths that are quite satisfactory for milk

rStraining purposes. Dairy farmers should not purchase cloths at stores

and cut them to a proper size because straining material must be uni-

form in thickness and of known sanitary quality. These cloths should

be a thin grade of outing flannel with a noticeable nap. Tests have

3 A S <5

M ír\ufes

3

IÓ li

Fig. 5.—The Rate at Which the Capacity or a Cotton Pad Decreases

with Use.

This is shown by the records of the total weight of milk which passed thru a

cotton pad at one-minute intervals. Jersey milk, free from sediment, at

90° was used.

17

shown that three to five cans of Jersey milk can be strained thru

one cloth flannel of the type mentioned. Such capacity makes it pos-

sible for the average large dairy farmer *to use one cloth per milking,

thereby eliminating the necessity of changing the cloth during the

milking process.

Some question is always raised concerning the relative merits of cloth

and cotton for straining purposes from the standpoint of the removal of

sediment. It is generally true that the slower the rate of straining the

more completely the sediment will be removed. When cotton is used

which will strain only one can of milk in 5 minutes when the funnel is

kept filled, nearly all of the visible sediment is removed. Similarly, if

a dense filter cloth with long nap is used that has a capacity equal to

that of the cotton, then practically all visible sediment will be removed.

On the other hand, when a thin flannel cloth is used the capacity is

markedly increased and the efficiency of removing sediment is de-

creased. The reason for such results is self-evident.

When milk is produced in a reasonably sanitary manner, straining

thru flannel will remove most of the sediment and will yield milk which

is sufficiently clean to be placed in the highest class by most milk in-

spectors. The milk may show a few specks on the sediment test disc

and will show a few specks in the bottom of a milk bottle after 24 hours'

standing, but the amount of this material is not sufficient to classify the

milk as unclean. Straining with this degree of thoroness ought to be

generally satisfactory. It is considerably more thoro than straining

milk thru a brass screen of 100 mesh, but it is not thoro enough to re-

move sediment from very dirty milk so completely that it will be classed

as clean. It is debatable whether a strainer should be used on the farm

that will produce an apparently clean milk from one that is actually

dirty. Furthermore, since all milk must be filtered or clarified in the

milk plant, there is no necessity for the complete removal of sediment

from milk on the farm.

Exception should be made to these statements where raw milk for

special trade is produced which will not be subjected to subsequent

filtration or clarification. Under such circumstances, a dense flannel

or special filter cloth or a cotton pad ought to be used to remove as

much visible sediment as possible. The straining material will clog after

straining from one to three cans of milk and there is no danger of wash-

ing sediment thru the cloth or cotton by continued use as long as it is

free from tears, holes, etc.

18

TEMPERATURE AND FAT CONTENT OF MILK AFFECT

STRAINING

The condition of milk at the time of straining influences the capacity

of a strainer to a great extent. The factor of most importance is tem-

perature. In the summer months milk is generally poured into the

strainer at a temperature varying from 90° to 95 °F, but during the

winter the temperature ranges from 75° to 85°F.

A series of tests have been made on Jersey and Holstein milk to show

the influence of temperature on capacity of straining. The results se-

cured with Jersey milk are shown in Fig. 6. Strainer No. 6 as shown

in Table 1 and in Figs. 2,3, and 4, was used in the tests. It was used

both with cotton and with flannel. It will be observed from the graph

6

/A í r% u t <2 3

FIG> 6,—The Length of Time Required to Strain Milk at Various Tempera-

tures and the Amount of Milk that Passed thru the Cotton Pads or

Cloths Before Clogging.

The tests were made with a strainer having a 6%-inch foot. The cloth was

fastened outside the funnel, while the cotton was supported on a wire grid.

w

19

that this strainer, using cotton, handled only one can of milk when the

temperature was 80° and less than one can at 75°. At 90° it was pos-

sible to strain four cans of milk satisfactorily. These results agree well

with experiences in straining milk at the dairy barn at this Station

during the winter and summer months and clearly illustrate that a

strainer may handle several cans of milk during the summer months

but might be entirely too slow during the winter.

One test is also shown on the graph illustrating results secured with

a flannel cloth straining milk at 80°. This cloth strained six to 10 cans

of milk without clogging, an amount which included the entire supply

available at the beginning of the test. It is evident that this straining

funnel when used with flannel which is not supported underneath will

strain any reasonable quantities of milk during either the winter or

summer months.

Altho it is hardly feasible to recommend the process for general

practice, it is interesting to note that the capacity of a strainer can be

greatly increased by a slight shaking after it has become clogged. It is

true that such shaking does not seem to affect the efficiency of straining

nor does it break the cotton when the cotton is properly supported with

good equipment in the straining funnel. The shaking consisted of

raising the strainer about 3 inches from the can and dropping it down

upon the can for three consecutive times. If the cotton should break

as a result of this treatment or the cloth should be torn loose, it would

be necessary to re-strain the entire can of milk into which the milk had

flowed after the accident occurred. It is for this reason that shaking

should not be practiced.

Cold milk strains much slower than warm milk due to the solidifica-

tion of the fat and to the formation of large clusters of fat globules. It

is these clusters of fat globules which form in cold milk that rapidly

clog the strainer.

Other things being equal, it would be expected that rich milk would

be strained with much more difficulty than thin milk. The capacity of

the strainer for handling milk is not decreased proportionately to the

increase in the fat content. For example, an increase in the fat con-

tent of milk produced by average Holstein cattle to that produced by

Jerseys will result in a decrease of approximately one-third in the total

capacity of the strainer.

WIRE GAUZE STRAINER

Wire gauze strainers have been extensively employed in former years

20

for straining market milk and are still used in some places. They have

come into disrepute largely because of the difficulties which have been

encountered by dairymen in properly washing and sterilizing them. tyj

Aside from this point, they have considerable merit because they have

great capacity and the effectiveness of removing sediment can be con-

trolled by the mesh of the gauze. The finest gauze that ordinarily can

be purchased is 125 mesh and this size does not remove sediment as sat-

isfactorily as flannel cloth. On account of the serious objection to wire

gauze by inspectors and plant operators, it is very doubtful whether it

will ever again become popular on the dairy farm in market milk areas.

It is but fair to state that brass wire gauze of 125 mesh was used at

the Station for about four months with entire satisfaction from a sani-

tary standpoint. The wire can be washed and sterilized, but it re-

quires extra precautions to keep the wire in good sanitary condition.

SUMMARY

The essential factors involved in milk straining on the farm may be

summarized as follows:

1. Milk ought to be produced under satisfactory sanitary conditions

irrespective of subsequent efficient straining. Straining has little

value in improving the sanitary qualities of milk.

2. Milk is strained primarily to improve its appearance and market-

ability. Complete removal of all visible sediment from milk on

the farm may discourage proper sanitary precautions and make it

difficult for inspectors to recognize dirty milk.

3. There is need for strainers of ample capacity to avoid the necessity

of changing cloths or cotton pads for each can of milk. Contami-

nation from hands in a wet strainer is very undesirable. It is

better to have an extra strainer than to change the cloth or cotton

during milking.

4. It is difficult to filter milk on the farm. Good straining is satis-

factory for ordinary milk because all milk must be filtered or

clarified in the milk plant where excellent facilities are available

for doing the work. Grade A raw milk or other milk sold raw

without clarification or filtration in a milk plant ought to be ¿j

strained thru cotton or heavy filter cloth to remove all sediment ^

possible.

•

21

5. A good milk strainer should embody the following factors:

a. Single-service cloths or cotton pads manufactured explicitly

for straining milk.

b. Easy washing and freedom from inside seams or outside

crevices, etc.

c. A capacity of at least two 10-gallon cans of milk without

clogging in the winter. This requires an outlet of maximum

size to fit the neck of the milk can for use with cotton.

d. Removal of most of the visible sediment.

e. Economical as to original cost, durability, and cloth or cotton

requirement.

6. Single-service cloths, according to the opinion of the author, are

more satisfactory for general use than cotton pads.

The advantages of cloths are as follows:

a. Greater capacity.

b. More easily fastened in or on the outside of the funnel.

c. Greater uniformity in results.

d. Less costly due to more milk strained per cloth.

e. Do not remove all of the very fine sediment, thus mak-

ing it easier for the milk inspector to detect dirty milk.

f. Hold less butterfat than cotton when clogged.

The disadvantages of cloths are as follows:

a. Less efficient removal of sediment than with cotton.

b. Greater cost per unit.

c. Possibility of re-using.

7. The cloth should be attached in or to the funnel, to give maximum

capacity and efficiency, as follows:

a. No milk should pass around the cloth.

b. There should be no support underneath when maximum

capacity is required.

c. Where less capacity is required the cloth can be used by

supporting it in the funnel like a cotton pad.

d. For outside attachment the cloth should be about 3 inches

larger in diameter than the outside diameter of the foot of

the funnel. Thus the Sy2-mch strainer requires an 8-inch

cloth, while the 6%-inch size requires a 10-inch cloth. If

the inside attachment is used, the size of the cloth should be

6y2 or 8 inches, respectively. In some funnels the cloth

should just fit the opening.

8. The cotton requires extra precautions for best results as follows:

a. No milk should pass around the cotton.

22

b. The cotton needs protection on the upper surface against

washing by the milk by both a cloth facing on the cotton and

a perforated conical or flat raised disc. If uniformly good f

straining is not essential, the plain cotton will prove satisfac- "™

tory and cheaper than cloth faced cotton.

c. The cotton needs to rest upon a coarse wire grid. There is

also a possibility of using a double cloth faced cotton pad

without support underneath, but the straining is less uniform

due to washing of the cotton.

d. Cotton is generally used with inside equipment, so for a Sl/¿-

inch strainer the cotton should be 6}4 inches, but the ca-

pacity of this size is usually too small. The 8-inch cotton

ought to be used in the 6%-inch strainer. One type of

strainer requires a small cotton that just fits into the strain-

ing funnel, while another type requires an outside fastening

with larger discs or squares of cotton.

9. The capacity of a milk strainer becomes less as the milk cools and

with increased percentages of fat. Cotton or cloth eventually clogs

with butter fat. This fact makes it very important to strain milk

as soon as each cow is milked.

10. The strainer shown in Figs. 2,3, and 4, illustrates certain desirable

features in milk straining. This strainer may be used with cloth

or cotton discs or squares on the inside of the funnel or with cloth

on the outside to give extra capacity for large dairies.

11. Strainers need to be thoroly washed and sterilized after each milk-

ing. They should be rinsed with cold water, then scrubbed with a

brush, using warm water and a mineral washing powder, rinsed with

or immersed in boiling hot water until thoroly heated and inverted

to dry. When steam is available they should be sterilized with it

in the usual way. A neglected strainer will become a source of

bacterial contamination no matter how well it is constructed from

a sanitary viewpoint.