11
OUR INDUSTRY TODAY Cheddar Cheese Yields in New York ABSTRACT Cheese yields and yield efficiency were monitored in four large Cheddar cheese plants in New York state. The yearly average theoretical Cheddar cheese yield for all four plants was 9.88 kgllOO kg of milk while the actual moisture and salt adjusted yield was 9.42 kg/100 kg. Major cheese yield losses were due to low fat recovery. Average milk fat recoveries in the cheese for the four cheese plants were 87.2, 86.3, 85.2, and 82.8%. Fat re- coveries were well below the 93 % fat recovery predicted by the Van Slyke formula. Primary factors related to poor cheese yields were low casein content of the milk, low ratio of casein to fat, and excessive mechanical breakage of cheese curd in the vats. A practical approach for estimating fat loss during cheese manu- factu re is described. INTRODUCTION Cheddar cheese yield is important to deter- mine the price of cheese. Accurate deter- minations of milk and cheese compositions are critical for calculating cheese yields. Differences in analytical techniques, record keeping meth- ods, and manufacturing conditions are a few of the problems encountered in collecting yield data from more than one plant . Casein and fat in milk and their ratio have profound influences on cheese yield that can be obtained under ideal manufacturing conditions. In the 1890's, L. L. Van Slyke (I7) studied the relationship of Cheddar cheese yield and milk composition in New York state. His formula relating yield to milk composition has been used since, in spite of sweeping changes of cheese manufacturing techniques. Received July 25.1983. D. M. BARBANO and J. W. SHERBON Department of Food Science Cornell University Ithaca, NY 14853 Our objectives were to quantitate Cheddar cheese yields in New York and to determine if fat and casein recovery in modern cheese factories are similar to those observed by Van Slyke at the turn of the century. MATERIALS AND METHODS Sampling Sam pies were collected at four Cheddar cheese factories in different geographic areas of New York State over 2 yr. Sampling procedures were designed specifically for each cheese plant so that results would be comparable between plants. To reduce plant variation, all sample analysis and record keeping were at the uni- versity. Table 1 indicates the number of study days in each plant for cheese yield and number of vats of cheese sampled in each of the four plants. A complete sampling routine was followed on a study day. Milk without starter, whey JUSt prior to draw, and cheese samples were taken from each vat. Other ingredients, by-products, and wastes were sampled and analyzed. Milk A"-alysis Each individual vat milk sample was tested for fat and protein with a Milko-Scan 300 calibrated against Babcock and Kjeldahl total nitrogen (TN) x 6.38 (3). In addition, a com- posite milk sample representing all vats each sampling day was tested by Babcock and Kjeldahl ro confirm the accuracy of the Milko- Scan results. These composite samples also were tested for casein content. Casein con tern was taken as TN minus noncasein nitrogen (NCN) x 6.38 (2, 9). Milk NCN was determined by our delivering 50 ml of milk at 20°C from a vol- umetric pipet into a clean dry screw-cap plastic vial. Milk was tempered to 40°C in 10 min, 1.5 ml of 33.3% (wt/vol) acetic acid solu tion was added, gently mixed, and then held at 40°C for 10 min. Next, 1.5 ml of 3.33 N sodium acetate was added, gently mixed, and held at 40°C for 1984 J Dairy Sci 67,1873-1883 1873

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OUR INDUSTRY TODAY

Cheddar Cheese Yields in New York

ABSTRACT

Cheese yields and yield efficiency were monitored in four large Cheddar cheese plants in New York state. The yearly average theoretical Cheddar cheese yield for all four plants was 9.88 kgllOO kg of milk while the actual moisture and salt adjusted yield was 9.42 kg/100 kg. Major cheese yield losses were due to low fat recovery. Average milk fat recoveries in the cheese for the four cheese plants were 87.2, 86.3, 85.2, and 82.8%. Fat re­coveries were well below the 93 % fat recovery predicted by the Van Slyke formula. Primary factors related to poor cheese yields were low casein content of the milk, low ratio of casein to fat, and excessive mechanical breakage of cheese curd in the vats. A practical approach for estimating fat loss during cheese manu­factu re is described.

INTRODUCTION

Cheddar cheese yield is important to deter­mine the price of cheese. Accurate deter­minations of milk and cheese compositions are critical for calculating cheese yields. Differences in analytical techniques, record keeping meth­ods, and manufacturing conditions are a few of the problems encountered in collecting yield data from more than one plant .

Casein and fat in milk and their ratio have profound influences on cheese yield that can be obtained under ideal manufacturing conditions. In the 1890's, L. L. Van Slyke (I7) studied the relationship of Cheddar cheese yield and milk composition in New York state. His formula relating yield to milk composition has been used since, in spite of sweeping changes of cheese manufacturing techniques.

Received July 25.1983.

D. M. BARBANO and J. W. SHERBON Department of Food Science

Cornell University Ithaca, NY 14853

Our objectives were to quantitate Cheddar cheese yields in New York and to determine if fat and casein recovery in modern cheese factories are similar to those observed by Van Slyke at the turn of the century.

MATERIALS AND METHODS

Sampling

Sam pies were collected at four Cheddar cheese factories in different geographic areas of New York State over 2 yr. Sampling procedures were designed specifically for each cheese plant so that results would be comparable between plants. To reduce plant variation, all sample analysis and record keeping were at the uni­versity. Table 1 indicates the number of study days in each plant for cheese yield and number of vats of cheese sampled in each of the four plants. A complete sampling routine was followed on a study day. Milk without starter, whey JUSt prior to draw, and cheese samples were taken from each vat. Other ingredients, by-products, and wastes were sampled and analyzed.

Milk A"-alysis

Each individual vat milk sample was tested for fat and protein with a Milko-Scan 300 calibrated against Babcock and Kjeldahl total nitrogen (TN) x 6.38 (3). In addition, a com­posite milk sample representing all vats each sampling day was tested by Babcock and Kjeldahl ro confirm the accuracy of the Milko­Scan results. These composite samples also were tested for casein content. Casein con tern was taken as TN minus noncasein nitrogen (NCN) x 6.38 (2, 9). Milk NCN was determined by our delivering 50 ml of milk at 20°C from a vol­umetric pipet into a clean dry screw-cap plastic vial. Milk was tempered to 40°C in 10 min, 1.5 ml of 33.3% (wt/vol) acetic acid solu tion was added, gently mixed, and then held at 40°C for 10 min. Next, 1.5 ml of 3.33 N sodium acetate was added, gently mixed, and held at 40°C for

1984 J Dairy Sci 67,1873-1883 1873

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1874 BARBANO AND SHERBON

TABLE 1. Number of sampling days in each cheese plant and total number of va ts of cheese in the yield evaluation.

Number of Number of Plant study days vats sampled

1 85 1,118 2 31 427 3 33 726 4 37 714

3 min . (Total volume of reagents added was 6% of the milk volume to offset reduction of milk volume from removal of casein and fat pre­cipitate.) The curd plus whey mixture was filtered through a fluted Whatman 1 filter, and that filtrate was passed through a Whatman 42 filter into a clean dry flask . This filtrate was clear and free from particles. Duplicate 5-g samples of this undiluted milk NCN filtrate were weighed for modified Kjeldahl analysis (9).

Composite milk samples were tested for nonprotein nitrogen (NPN) content by 5 g of milk weighed into an Erlenmeyer flask and 5 ml of 24% trichloroacetic acid (TCA) added. After 30 min at room temperature, the mixture was filtered through a Whatman 42 filter. The original flask was rinsed twice with 10-ml samples of 12% TCA. The TCA rinses were added to the filter and collected with die original clear and particulate free filtrate . The total filtrate was transferred quantitatively to a macro-Kjeldahl flask. Kjeldahl analysis (3) was titrated with .01 N HCI instead of .1 N HC!.

Cheese Sampling and Analysis

One block of cheese was sampled from the middle of the run from each vat on each day. Three days after manufacture, six cores (10 cm x 1.5 cm) were taken from each sample block in a specified pattern to reduce sampling error. All six cheese cores were cooled to refrigerator temperature and ground together in a blender to obtain a particle size of about 2 to 3 mm . Samples were packed in 56.7-g plastic universal milk sample containers (without head space) to minimize moisture loss from the cheese during storage (up to 4 days at SoC). All cheese samples were analyzed fresh during the same week they were taken.

Journal of Dairy Science Vol. 67 , No.8, 1984

Cheese from each vat was anal yzed in duplicate for moisture, fat, protein, and salt . Moisture was determined by 2-g cheese samples dried for 24 h in a forced air oven at 100°C and weight loss ascertained (1) . Fat content of cheese was determined by a modified Babcock test (1) with New York state-certified 50% cream test bottles, 9-g sample, 10 ml of boiling water , regular Babcock sulfuric acid, and glymol red. Kjeldahl TN determinations (3) for each vat of cheese were converted to protein basis (N x 6.38). Salt content of each vat of cheese was determined by the Volhard pro­cedure (1).

Whey Sampling and Analysis

Whey samples were taken from vats JUSt before draw. Samples were frozen immediately and held for analysis. Freezing stopped acid production by starter organisms and proteolysis by proteolytic enzymes in whey . Whey from each vat was analyzed in duplicate for fat content by a modified Babcock procedure (1)

in skim test bottles. This procedure gave results that compared well with the Roese-Gottlieb ether extraction method (1) for whey samples taken from cheese vats (>. 15% fat). The modified Babcock procedure for whey gave low results in comparison with the Roese-Gottlieb method on samples of whey taken from a cream separator.

Cheese Manufacturing Plants

All four cheese plants used between 225,000 and 460,000 kg of milk per day to manufacture Cheddar cheese. Three cheese ~Iants made cheese from heat treated milk (65 C for 21 s). The other plant used fully pasteurized milk part of the year and heat treated milk the rest of the year. Manufacturing conditions varied from plant to plant, but all cheese making procedures were about 5 h from starter addition to milling. All plants used conventional bulk starter cultures and (50 :50) rennet:porcine coagulants. The general type of equipment in each plant was as follows.

Plant 1. Equipment was 16,364-kg capacity closed top circular vats with built in cu tting and stirring, automatic cheddaring, and au tomatic salting.

Plant 2. Equipment was 16,364-kg capacity open rectangular vats with one traveling agitator, cheddaring tables, and salting tables.

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OUR INDUSTRY TODAY 1875

Plant 3. Before renovation, equipment was 8,182-kg capacity open rectangular vats with three traveling agitators per vat, automatic cheddaring, and salting tables. After renovation, it was 16,364-kg capacity closed top circular vats with built in cutting and stirring, automatic cheddaring, and sal ting tables.

Plant 4. Equipment was 16,364-kg capacity open rectangular vats with one traveling agitator, automatic cheddaring, and salting tables.

Yield Determination

Actual cheese yield was determined by weighing each individual block of cheese to the nearest .045 kg. Total kilograms of cheese per vat and per day were calculated. Cheese weights were determined after pressing (day 1).

The amount of milk in each vat was determined by calibrated sticks. Accuracy of milk and cheese weights was verified by the Federal Order Number 2 Market AdminiStrator's Office.

Theoretical cheese yield was calculated by the Van Slyke cheese yield formula: Theoretical yield = [.93 Fat + (Casein - .1)) 1.09/[1 -(Desired cheese moistureIIOO)]. Theoretical

yields were calculated on a desired cheese moisture content of 37%. The 1.09 factor in the theoretical yield formula assumes a 1.7% salt content in the cheese. Actual yield is based on milk weight in the vats (does not include starter, coagulant, color, CaCI 2 , or water used to disperse these additives) and weight of cheese after pressing. Composition-adjusted yield is a mathematical calculation of the weight of cheese that would have been obtained if moisture was 37% and salt was 1.7%. Com­position-adjusted yields allow direct com­parisons of yields from day to day, plant to plant, or to theoretical yield for equal com­position.

RESUL TS

Milk Composition

Milk received at New York state Cheddar cheese plants showed the expected seasonal variation of milk fat content (Figure 1). Day­to-day variability of milk fat (Table 2) averaged .5% throughout the year.

summer winter summer winter

MONTHS Figure I. Seasonal variation in the fat content of milk received at four Cheddar cheese plants in New York.

Journal of Dairy Science Vol. 67, No.8, 1984

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1876 BARBANO AND SHERBON

TABLE 2. Ave rage annual fat and casein content of :nilk received at four Cheddar cheese plants in New York.

Plant

1 2 3 4

Observations

(days)

85 31 33 34

Fat

(%)

X SEa

3.69 . 11 3.58 .14 3.57 . 14 3.66 . 11

Fat rangea

.47

.44

.54

.46

Casein

X

2.44 2.38 2.46 2.46

SEa

.06

.08

.09

.06

(% )

Casc in rangea

.27

.32

.36

.25

aStandard errors and ranges reflect variability and high/low diffe rences, respectively, in daily means, not vat-to-vat variation within day.

Casein content of milk showed seasonal (Figure 2) and plant-to-plant differences (Table 2). These cheese plants averaged .3% difference in casein content of their milk supply, seaso·nally. Casein as a percent of total true protein (TN -NPN) varied from 76.5 to 82 .4% and averaged close to 80% for all plants (Table 3). Proper

. ratio of casein to fat in milk is important for obtaining optimum cheese yields. Average yearly ratios of casein to fat differed from

3.

Z 2.

plant-to-plant as in Table 4. Optimum ratio of milk casein to fat is .7 for Cheddar cheese manufacture (17). However, the four cheese plants had milk supplies that were below .7 ratio of casein to fat.

Cheese and Whey Composition

Average cheese composition for four cheese plants is in Table 5. Differences in cheese moisture and salt content from plant to plant

W summer winter en summer winter

« 2. <.)

~ 2. -' ~

2.

2.

MONTHS Figure 2. Seasonal variation in the casein content of milk received at four Cheddar cheese plants in New

York.

Journal of Dairy Science Vol. 67 , No . 8, 1984

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OUR INDUSTRY TODAY 1877

TAIlLE 3. Yearly average milk casein as a percent of total rrue prorein.

Casein as a percenr of rrue

Planr Days prorein Range"

X SEa ( 'Yo )

!IS 79.!I% .7 77.7 ro 81.7 2 31 79.2%· 1.0 76.S to !l0.7 3 33 80.4% 1.1 78.4 to 82.4 4 34 80.2% .8 78.3 to 81.8

"SrandarJ errors and ranges reflecr variability "nJ hi)o!h / low Jifferences. respecrively . in Jaily mean casein as a percent of toral rrue protein (toral nirro­gen - nonprotein nitro)o!cn), not vat-to -var variatiOn within a Jay.

demonstrated that mathematical adjustment of actual yield data to an eljual moisture and salt basis was nccessary for valid comparisons of l'iclJ. As expected. moisture was near 37% and fat on a dry basis (F 0 B) was over 50%. Sal twas near 1.7% in three plants but only 1.43 in the fourth plant. Considerable day-to-day variation of salt in rhe aqueous phase of the cheese was observed . This variation may be one of the major reasons for differences in flavor develop­ment and cheese texture during aging.

Cheesc protein on a dry basis (POB) is not measured commonly or reported for cheeses; however. substantial differences in POB werc observed betwcen plants. Fresh grou nd cheese samples with a high POB had a firmer texture and drier appearance than low PDB cheese even when moisture assays were the same.

Failure to achieve theoretical yields. based on actual milk casein and fat content. imrlies

that some casein and fat were lost during

ttt n\~\I\lb.c.t\lt\\I% \ltocess. \l'\t\a. \osses oc.c.uneo. • .1 c \o'ou\es, s()\u\)k t\\L)ffi'a.i.\C.

'd.~ c.\:,?useu tat g f . and filterab\e ducts 0 caseIn. .

breakdown pro . b th fat and caseInS curd fines that contalll h

O Table 6 lists the

were expeJ\ed into thef

wh

ey ~hey ar draw for f t ontent 0 t e

average a c of whey fats were h Plant Averages each c eese· like small

3 and .4% _ These seem between. b uantitatively they represent differenceS. ur q . ld Generally

Cheese Yields

ACLUal. moisture-adjusted and salt-adjusted. and theoretical cheese yields for all four plants are in Table 7. These yields are based on total milk and cheese for the day rather than upon individual vat data. There were plant-to-plant differcnces in theoretical yields as would be expected from obscrved differences in milk composition (Table 2). Average composition adjusted Cheddar cheese yield for all four plants in this study was 9.42 kg / IOO kg of milk, whereas average Van Slyke rheoretical Cheddar cheese yield for all four plants in the same time period was 9.88 kgllOO kg of milk. The four plants averaged 95.3% of theoretical yield predicted by the Van Slyke equation.

The Van Slyke cquation assumes that a Cheddar cheese plant should be able to recover 93% of the original milk fat in the finished checse. All cheese plants averaged below 93% fat recovery in the finished cheese (Table 8). Van Slyke estimated that casein recovery in the cheesc would be the milk casein minus 1% which would be about 96%. Observed ~asdin recoveries averaged Ilear this value (Table 8) but showed considerable variability from dav to dav. Casein recovery in the cheese. actually' includes J small amount of whey protein that is in the aqueous phase of the cheese. If cheese cOlltains 37% moisture and that moisture contains about .7% soluble whey protein. then there would be about .26% of whcy protein present in normal Cheddar cheese, which is about 1% of the total protein in the cheese. Therefore. the true casein recovery in cheese is abou t 1 % less than the recovery

Plant Days Ca,einffat ratio Rangea

X Sf

.662 .016 .08 1 85

.019 .07 .667 2 31 .026 .10 .689 3 33 .018 .07

4 34 .674

anJ ranges reflect variability anJ T losses of cheese Yle .

sign! lcant f ilk casein to fat within a plant when ratlOS 0 m f the whey at draw decreased. fat content 0

"StanJaru errors . ' Jail mean /I differences, respectively. In. Y h'

high ow rat'los. not vat-to-vat variation WIt III a casein/fat uay.

increased.

Journal of Dairy Science Vol. 67, No.8. 1984

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1878 BARBANO AND SHERBON

TABLE 5. Yearly average Cheddar cheese composition in New York.

Plant

Plant I, Plant 2, Plant 3, Plant 4, 85 days 31 days 33 days 34 days

X SEa X SE X SE X SE

Moisture 37 .13 .94 37.35 .49 36.63 .50 37.28 .39 Fat 33 .32 .68 32.67 .59 32.81 .56 32.24 .33 Protein 24.02 .67 24.41 .46 25.11 .58 24.86 .53 Salt 1.43 .20 1.65 .18 1.77 .12 1.72 .08 Fat on a dry basis 52.99 .68 52.14 .82 51.77 .64 51.39 .41

Protein on a dry basis 38.19 .86 38.97 .61 39.63 1.07 39.68 .80

MNFS b 55.68 1.02 55.47 .64 54.51 .51 55.02 .45 Salt in

moisturec 3.85 .59 4.41 .50 4.85 .35 4.60 .97

aStandard errors reflect variability in daily means for all vats, not vat-to-vat variability. b .

MNFS = Moisture as a percent of nonfat subsrance.

cSalt in the aqueous phase of the cheese was determined by dividing cheese percent salt by percent moisturc.

reported in Table 8. When the whey protein content of cheese was considered, the average casein recovery for all cheese plants was esti­mated to be 93.9%.

Total fat and casein was accounted for in each cheese plant each sampling day. All plants had a disappearance rate of fat of 1 to 2%. Exact determination of fat losses on equipment surfaces in large cheese plants was not easy. However, significant fat losses were observed on surfaces of the 18-kg stainless steel hoops and

in the fabric of the cheese press cloths. In one plant it .was estimated that as much as .5% of the ongmal milk fat could be lost on these

surfaces and not accounted fa . h . f r In t e Input/

bou tpu t at records. Total casein recoveries were

etween 100 and 1020/, C . o. aseln recoveries

great~r ~han 100% maybe due to the whe protein Included in the cheese as d 'b dY Acc 'lk eSCrI e

urate ml weigh t determinations ar~ Important. for determ ining fat and casein accountabIlIty. The market d . . '. a mmlstrator's

au~It and JUStification of farm milk wei h agamst mIlk utilized for cheese making hel

g ~ detect errors in milk weight dete . . pe h rmmatlon at

t e cheese plants.

Data from actual fat and casem recovery showed that the greatest losses of theoretical

Journal of Dairy Science Vol. 67, No.8, 1984

cheese solids were from milk fat. However, both types of losses are significant, and the magnitude and relative importance of these losses may differ both seasonally and from plant-to-plant . The average ratio of milk casein to fat and the seasonal variation in this ratio are important determinants to recovery of fat and casein in cheese.

TABLE 6. Yearly average far conrenr of Cheddar cheese whey at draw.

Plant Days % Fat Minimum a Maximum b

X SEa (%) 85 .31 .04 .23 .40 2 31 .41 .06 .36 3 .59 33 .34 .04 .27

4 34 .42 .40 .03 .35 .49

a b L~west daily average whcy fat.

HIghest daily average whey far. c

. Standard errors reflect variabiliry in daily means tor all vats, not vat-rO-var variabiliry .

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OUR INDUSTRY TODAY 1879

TABLE 7 . Average yearly actual, moisture and salt adjusted, and theoretical percent y ields of Cheddar cheese in New York.

Plant Actual yielda Adjusted yieldb Theoretical yield C

2 3 4

X

9.64 9.43 9 .25 9.40

SEd

.27

.33

.35

.15

Rangee X SE

1.19 9.64 .24 1.22 9.38 .33 1.33 9.28 .38

.71 9.36 .16

Range X SE Range

1.11 9.98 .26 1.04 1.18 9.72 .33 1.04 1.37 9 .81 .34 1.33

.82 10.00 .25 .91

aActual yields were determined for the day by dividing total kilograms of cheese by total kilograms of milk used multiplied by 100.

b Adjusted yields were determined by mathematically correcting kilograms of cheese for each vat for the day to a 37% moisture and 1.7% salt. Total adjusted weights from all vats divided by total milk used in all vats equals total adjusted yield.

cTheoretical yields were based on milk fat and casein content of the milk on the same days as actual and adjusted yields were measured. The Van Slyke formula was used with a 93% fat recovery and 37% moisture .

dStandard errors reflect variability in daily mean yields not vat-to-vat variability. Total number of days per plant is the same as in Table 1.

eRange equals difference in yield between the day with the highest yield and the day with the lowest yield.

DISCUSSION

Cheese Yield Potential

Cheese manufacturing companies need to be conscious of their product yield. Management needs to know both the theoretical cheese yield potential and composition-adjusted cheese yield to evaluate plant performance. Low yields can result from milk with low "cheese" solids con-tent (i.e., casein and fat), poor recovery of casein and fat, or a combination of both of these factors.

The yield potential of milk is a factor over which management has little control. Ad-

justments of milk composition by standardiza­tion can be accomplished, but may not be cost effective. There were substantial plant-to-plant differences in theoretical cheese yields due to differences in milk composition (Table 7). All four plants had mean theoretical cheese yields well below the 10.1 kg/IOO kg milk that usually is referred to as "average" in the United States. Differences in yield potential from plant to plant are important when attempting to compare one factory with another.

Determination of cheese yield potential of a milk requires representative sampling and accurate analytical procedures for casein

TABLE 8. Average annual fat recovery and estimated casein recovery in Cheddar cheese made in New York.

Plant Days Fat recovery Casein recoverya

X SEb X SE

1 85 87.16 2.03 95.28 2.22 2 31 86.29 2.13 96.06 2.35 3 33 85.18 2.90 94.50 3.14 4 34 82.83 2.26 93.57 2.30

aInciudes a small amount of whey protein that is soluble in the aqueous phase of the cheese. Therefore, the casein recovery data shown above may be an overestimate by about 1 %.

bStandard errors reflect variability in daily mean recovery in the cheese.

Journal of Dairy Science Vol. 67, No.8, 1984

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1880 BARBANO AND SHERBON

and fat . Determination of milk fat is a highly regulated and scrutinized activity in the dairy industry. Accura te casei n determina t io ns are just as important, but analytical methods fo r casein have not been refined to th e same exte nt as methods for milk fat.

The method used to measu re casein ill milk can influence the result. Results of Van Slyke (17), Herrington et a1. (8), and our results for milk casein in th e :-Jew York milk supply are an illustration of this problem. Van Slyke (17)

observed milk casein of 2.47,2.47, and 2.41 % in 1892, 1893, and 1894. Herrington et al. (8) found New York milk casein was about 2.27% in 1959 to 1960. In our study, the average milk casein was about 2.44%. Van Slyke did not report his method for measuring casein with his data on cheese yield. However, in anoth er publication by Van Slyke (16), he desc'ribes a method for determining casein content of milk. This method was an acetic acid precipitation of casein and determination of T N of the casein precipitate by the Kjeldahl method. A 6.25 factor was u sed to convert nitrogen to casein. The procedure described by Herrington et al. (8) for casein determillation was precipitation o f casein with rennet (rather than acid) and subtracting the rennet whey TN from milk TN. Rennet proteolyzes K -casein to form a milk coagulum and, therefore, would be expected to

. give lower casein results than acid precipitation of casein. This e x p lains most of the difference between Herrington'S results and those from the other two studies. Herrington et al. (8) defended their method by pointing ou t that it was more analagous to Cheddar cheese manu­facture.

There is a variety of methods available fo r casein analysis . The Association of Official Analytical Chemists (3) allows for measure­ment of casein nitrogen directly in whey free acid curd (method 1) or by subtracting NCN from TN (method 2). Filtrates that are free of precipitate are easier to obtain than precipitates free of filtrate. The International Dairy Federa­tion method (9) for casein determination subtracts NCN from TN in the original milk and compensates for the volume of the milk casein plus fat precipitate. The basis for the acid precipita tion methods is the Rowland (12) scheme for fractionation of the nitrogenous components of milk. Milk samples intended for casein analysis should be as fresh as possible.

Journal of Dairy Science Vol. 67, No .8, 1984

Proteolysis, which occurs in all milk during storage , c;tuses underestimation of milk casein.

Dye bIlldi ng methods have becn used for estimation o f prote in and casein content of bovinc milk (7,11,13). Because the dye binding capacity of whey protein and cascin arc significan tly di ff >re nt, it is assumed that all milks have the sam e relative proportions of caseins and whey proteins. Results indicate that there is su bstantial seasonal variabil it)' of this ratio (Table 3). This limits accurac y of dye binding meth od s for casein determ ination.

Cheese Yield Efficiency

Man y studies have documented similar seasonal variation of milk composition (8, 15 , 19) and milk protein variability (5, 7) Sea­sonal variation of milk fat anJ case in content is the major reaso n for seasonal variation of cheese yields (4, 6, 10, 14). Seasonal variation of milk composition influences both cheese yield pote Iltial and manufacturing effici ency.

Manufacturing plant performance is based upon how efficiently that plant is coIlverting theoretical cheese solids from its milk supply into actual cheese yield. If data fro m Table 7 are used to calculate a moisture and salt adjus ted yield as a percent of theoretical yielJ, plants 1, 2,3, and 4 had cheese yield efficiencies of 96.6, 96.5, 94.6, and 93.6%. Plant 4 had th e highest theoretical yield potential but was th e most inefficient a t converting this into actual cheese yield. This particular plant had high fat losses in whey, thus lim ited fat recovery in the cheese (Tables 6 and 8). Plant 4 also had more whey fine s collected per day (lower case in recovery in the cheese). Plant 2 had about the same amount o f fat loss in the whey up to draw (Table 6) as plant 4. But plant 2 did not lose as many fines because it \Vas using a different type of cheddaring equipment. Thus, plant 2 had higher cheese yield efficiency than plant 4. Generally, both plant 1 and 3 had lower fat losses in whey than plants 2 and 4. These differences in fat loss were related to differences in agitator design of the cheese vats.

Seasonal variations of ratio of milk casein to

fat and total casein plus fat in the milk make it difficult for a cheese manufacturer to: 1)

optimize process conditions to obtain maximum recovery of theoretical cheese solids and 2) control finished cheese composition. Cheese composition data (Table 5) underscore the

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difficulty of composItIon control in cheese manufacturing. Compositional variation from vat to vat (not shown) was much greater than the day-to-day variation in Table 5. Variability of cheese composition can result in lower yields and extreme variation of flavor and quality of finished product. Methods of cheese manu­facture that result in more consistent product composition and quality are needed .

Overall, the Van Slyke equation did well predicting magnitude and dircction of changes of cheese yield. However, all plants had moisture and salt-adjusted cheese yields below those predicted by the Van Slyke equation. Fat recoveries were wcll belo w 93%. Casein re­coveries were lower than casein minus .1 but were closer to theoretical than fat rccoveries. Thc 1.09 factor in the Van Slyke equation allows a cheese salt content of about 1.7% plus some minerals and whey solids that will bc retaincd in the cheese. If data on cheese com­position (Table 5) are used to back calculate this factor (salt content adjusted to 1.7%), we found that thc factor would be 1.098 averaged across all factories in this study. The difference between the factor calculated from our ob­servations and Van Slyke's would not be significant because of extreme variability normally cncountered in Cheddar cheese composition. The Van Slyke formula remains an extremely useful tool for predicting the­oretical cheese yield for optimizing Cheddar cheese manufacturing practices .

Practical Method of Relative Fat Loss Estimation

Most cheese plants do not have laboratory facilities to measure routinely milk casein and perform the type of theoretical cheese yield monitoring that was done in our study. In all four cheese plants, low efficiency of fat recovery in the cheese was a major reason why com­position-adjusted cheese yields were not equal to theoretical cheese yields . Fat content of cheese whey at draw is a good practical index of loss of cheese yield . A reasonably simple yet reliable method of accurately estimating the relative percent fat recovery in a cheese plant from day to day is described. a) Measure the total weigh t of milk in each vat and percent milk fat to calculate an estimate of total milk fat available per day . b) Subtract kilograms of cheese obtained from each vat from kilograms

of milk used for each vat. This will give a rough bu t consistent index of total kilograms of whey for each vat. Determine the fat percent of the whey at draw from each vat, and multiply it by the estimated weight of whey to obtain the total kilograms of fat in the whey. c) The kilograms of fat in the original milk minus kilogram of fat estimated in the whey divided by the kilograms of fat in the original milk gives a relative evaluation of fat recovery up to draw. This can be used to monitor manufacturing performance from day to day. To obtain the theoretical yield of cheese, the fat recovery estimated at draw should be about 95% . In practice this is not achieved with unstandardized milk when the ratio of casein to fat is signifi­cantly below .7. Generally, our experience has been that as fat recovery decreases, casein recovery may decrease depending on the particular cheese making equipment .

This method has several advantages over using kilograms of fat in the cheese divided by kilograms of fat in the milk. Most of the fat lost during Cheddar cheese making is lost into the whey by the end of cooking (18). The fat test on whey and milk can be determined to the nearest .01 % by testing methods commonly used in a cheese plant, whereas the fat test on cheese by routine Babcock procedure estimates fat only to the nearest .5%. If milk and whey samples are taken from the vat during mixing, sampling error will be small. Estimating the amount of whey by subtracting the weight of cheese from the weight of milk causes an absolute error in weight of milk to cancel out of the calculation. Weight of whey calculated in this manner includes whey losses at su bsequent steps and overestimates the amount of whey at draw by about 1 to 2%. In spite of this limita­tion, this simple approach identifies relative changes of fat recovery as milk composition changes or when changes are made in the cheese making procedure prior to draw. A much faster turn around of information can be achieved by this approach than that obtained from cheese analyses that usually are completed several days after the cheese was manufactured . Fat recovery estimations based on total kilograms of fat in the cheese will be much more variable than those by the method described, but they also should be done routinely to determine if there are any unexpectedly large losses of fat during the cheese manufacturing process after draw .

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1882 BARBANO AND SHERBON

Many factors contribute to poor cheese yield efficiency. First, with respect t o milk com­position, low casein plus fat, low ratio of casein to fat, and variability of both of these factors makes it difficult to adjust cheese manufacturing procedures to obtain good cheese yield ef­ficiency. Second, differences in cheese making equipment design and equipment oper.ation can result in substantial differences in cheese yield efficiency. Fat losses in the whey were lower in plants 1 and 3 with closed top circular vats as compared to coventional rectangular vats with one traveling agitator as used in plants 2 and 4 . All of the same basic principles of good Cheddar cheese making procedures apply today as they did in the 1890's when Van . Slyke studied Cheddar cheese yield. Use of modern equip­ment designs, new cheese making procedures, and substitute ingredients must be done with a recognition of the principles of good cheese making . Third, cheese making skill is definitely a factor at all times , but the previous two factors will impose upper limits of recovery efficiency.

CONCLUSIONS

Average yearly theoretical Cheddar cheese yields (9.88 kg / lOO kg) and actual composition adjusted Cheddar cheese yields (9 .42 kgllOO kg) in New York State are both well below a 10.1 yield used as a basis in some pricing formulae .

A major reason for low actual cheese yields was excessive loss of fat during cheese making. Some of the differences in cheese yield ef­ficiency were related to differences in equ ip­ment design.

The Van Slyke cheese yield formula predicts higher cheese yields than the actual composition­adjusted cheese yields in New York, but the Van Slyke formula is still useful for improving in-plant cheese yield. Van Slyke theoretical cheese yields still may be obtainable with well designed modern cheese making equipment, if the ratio of milk casein to fat is .7 and an excellent milk coagulation is obtained.

Information obtained in this study benefited all companies in this research project. Since the end of this research project, all four companies have made substantial improvements in their efficiency of theoretical cheese solids recovery. This research project is an example of how

Journal of Dairy Science Vol. 67, No.8, 1984

university and dairy industry personnel from several different companies can work together while at the same time respecting the proprietary aspects of certain portions of cheese making technology of individual companies.

ACKNOWLEDGMENTS

Au thors thank Margaret Jacobs, Robert Merrill, Laura Dorfmann, Maureen Chapman, and George Hough ton for their technical assistance in sample and data analysis. We sincerely appreciate the cooperation and input of personnel from the various cheese plants. We thank the audit team and the Milk Market Administrator, Federal Order Number 2, for their aid in documenting milk utilization and cheese inventories. Analytical support and aid in refrigerated transport of samples by the New York Dairy Herd Improvement Cooperative was valuable to this study. Financial support from members of the New York Cheese Manu­facturers' Association and Dairy Research Inc. is acknowledged gratefully.

REFERENCES

1 American Public Health Association . 1978. Stan· dard methods for thc examination of dairy pro­ducts. 14th edition. Am . Pub!. Health Assoc., Wash­ington, DC.

2 A~chaffenburg, R., and J. Drewry. 1959. New procedure for the routine determination of the various non-casein proteins of milk . XV Int. Dairy Congr. 3(Sec. 5): 1631.

3 Association of Official Analytical Chemists. 1980. Official Methods of Analysis - 13th edition. Assoc. Offic. Anal. Chem., Arlington, VA 22209.

4 Banks, J. M., W. Banks, D. D. Muir, and A. G. Wilson. 1981. Cheese yield - composition does matter. Dairy Ind. 1m. 46(5): IS .

S Barnard, S. E., and G. L. Hargrove. 1975. Protein content of raw and fluid milk products. J. Milk Food Technol . 38:380.

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7 Grappen , R., V. S. Packard , and R. E. Ginn. 1981. Variability and interrelationships of various herd milk components. J. Food Prot. 44 :69.

8 Herrington, B. L. , J W. Sherbon. R. A. Ledford, and G. E. Houghton. 1972. Composit ion of milk in New York State. New York's food Life Sci. Bul!. 18: 1.

9 International Dairy Federation. 1964. Deter· mination of the casein content of milk. Int. Dairy Fed. Stand. No. 29. Int. Dairy Fed., Bruxelles, Belgium_

10 Lundstedt, E. 1979. Factors affecting the yield of cheese. Dairy Ind . Int. 44(4):21.

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11 McCann , T.C .A., A. Math iasscn , anu J . A. O'Con­nell. 1972. Applicat ions of the Pro-Milk MKII. Part III. Rapid est imation of casein anu protein in milk and whey. Lab. Prac. 2L628.

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13 Sherbon. J. W. 1975 . Collaborative study of the Pro-Milk mcthou for the determ ination of protein in milk. J. Assoc. Offic . Anal. Chern. 58 : 770.

14 Spurgeon. K. R., J. J. Yee, and J . II. Martin. 1981. Selection of milk for maximum yield of cheese and other uairy prouucts. Cult . Dairy Prou . J. 16(3):5.

15 Szijarto, L., D. A. Biggs, anu D. M. Irvine. 1973. Variability of casein, serum protein , anu non-protein

nitrogen in plant m ilk supplies in Ontario. J. Dairy Sci. 55 :45 .

16 Van Sly ke, L. L. 1893 . The determination of the casein content in cow's milk . H. W. Wiley, ed. Page 109 Ell USDA Div. Chern. Bull. No . 38. '

17 Van Slyke. L, L. 1894. Investigation relating to the manufacture of cheese . New York Agric. Exp. Sen. Bull. 65 .

18 Wilster, G. H. 1974. Practical cheesemaking. Oregon State Univ. Book Stores, Corvallis, OR.

19 Yee, J. J., and K. R. Spurgeon. 1979. Seasonal and regional differences in the composition of cow's milk in South Dakota. South Dakota State Univ. Tech. Bull. 46. Brookings.

Journal of Dairy Science Vol. 67, No.8, 1984