cooking times, cooking losses and energy used for cooking lamb roasts

COOKING TIMES, COOKING LOSSES AND ENERGY USED FOR COOKING LAMB ROASTS

C. L. GRIFFIN', J. W. SAVELL. G. C. SMITH, K. S. RHEE and H. K. JOHNSON'

Meats and Muscle Biology Section Department of Animal Science

Texas Agricultural Experiment Station Texas A& M University

College Station, TX 77843

Accepted for Publication: May 10, 1984

ABSTRACT

Cooking times and losses were monitored during cooking of ten each of eight kinds of lamb roasts. Roasts were cooked (163OC oven, not preheated) to be rare (6OoC), medium (7OOC) or well done (77OC). Cooking times and cooking losses significantly increased with increasing degrees of doneness. Cooking time recommendations were made based on the data I n a second study, cooking times, cooking losses and energy consumption were monitored during cooking o f 100 each o f boneless legs and boneless shoulder roasts. Ovens were either non-preheated or preheated and roasts were fresh, frozen, thawed 12 h at 21 "C, thawed 24 h at 1 O C or thawed by microwaves. Gas consumption was slightly less for boneless shoulders roasted in non-preheated ovens (21.2 cu. ft.) than for those roasted in preheated ovens (22.6 cu. ft.). Cooking times and losses were lower for fresh boneless shoulders and leg roasts versus those in the frozen or frozen- thawed treatments. Statistically significant differences in gas consump tions for the five treatment groups were observed, but differences in cost of purchased energy were negligible.

'Present address Princeton Packaging Corporation, Flexible Division, 1006 Alma Street, Dallas, TX 75215. *National Live Stock and Meat Board, 444 N. Michigan Ave., Chicago, IL 60611.

Journal of Food Quality Vol. 8 #2/3 (1985). 69-79. All Rights Reserved 0 Copyright 1985 by Food & Nutrition Press, Inc., Westport, Connecticut.

69

70 GRIFFIN, SAVELL, SMITH, RHEE AND JOHNSON

INTRODUCTION

Relationships of cooking times and temperatures to cooked meat palatability were studied in the early 1900s. Much of that research was published in experiment station bulletins but not in refereed scientific journals. In addition, beef was studied more extensively than lamb (National Live Stock and Meat Board 1942). Since those original studies were conducted, advanced technology has resulted in more sensitive temperature-monitoring equipment and different oven styles.

In addition, changing life-styles of consumers and increasing energy costs have led to increased interest in rapid, efficient cooking methods. Drew and Rhee (1978) compared different cooking methods for beef roasts and concluded that roasting in an oven utilized the greatest amount of energy when compared to cooking on a surface unit or in a portable appliance (microwave, slow cooker, etc.). Drew et al. (1980) found that cooking beef roasts from the frozen state used more energy than did cooking from the thawed state, regardless of whether the roast was cooked in a conventional or microwave oven.

Because limited research of this kind has been conducted with lamb, this study was conducted to: (1) update cooking recommendations for lamb roasts, and (2) compare cooking times, cooking losses, energy consumption and shear force values of boneless shoulders and legs of lamb roasted from fresh, frozen or thawed states in ovens which were or were not preheated.

EXPERIMENTAL

General

Two hundred-forty roasts, 30 each of eight different types (Part 1) and 100 each of boneless shoulders and boneless leg roasts (Part 2) were obtained from lamb carcasses weighing 25-30 kg. Carcasses were fabricated according to the procedures outlined in the Lamb Cutting Manual published by the American Lamb Council and the National Live Stock and Meat Board. All roasts were trimmed to a maximum of 6 mm external fat thickness.

Part 1

The eight types of roasts included: whole, bone-in leg; shank-half leg; sirloin-half leg; boneless leg; boneless shoulder; pre-sliced shoulder;

COOKING LAMB ROASTS 71

seven-rib rack; and crown rib. Carcasses were fabricated (about seven days postmortem) and roasts were prepared and held (2OC) for 14-16 h prior to roasting. Each roast was placed with the fat side up on a broiler rack in a non-preheated oven. Ten cuts of each type were roasted to rare (6OoC), medium (7OOC) and well-done (77OC). Internal temperature of each roast was monitored using two thermocouples placed in its approximate geometric center. Copper-constantan thermocouples (40 gauge; 0.008 cm diam), attached to a recording thermometer, were used to avoid influencing cooking time due to heat conduction into the meat (Hostetler and Dutson 1977). All roasts, except the seven-rib rack and crown rib, were cooked in gas ovens at a setting of 163OC.

In a preliminary study, seven-rib rack and crown rib roasts were cooked at each of three oven settings ( 1 6 3 O , 191O and 218OC) to each of three different degrees of doneness (60°, 70° and 77OC). It was noted that in 163OC ovens, the fat on the racks was a creamy white and had an uncooked-like color particularly when racks were cooked to rare (6OOC). At oven temperatures of 218OC, both seven-rib and crown rib roasts appeared charred; this was especially true of the rib ends on the crown rib roasts. Charring was partially prevented by inverting the crown roasts for the first half of the cooking period. Also, at higher oven temperatures, there was considerable fat spattering. Thus, it was decided that the remaining seven-rib rack and crown rib roasts should be cooked at 191oc.

Cooking time was recorded for each roast. Initial and final weight of each roast was recorded and cooking loss was calculated as a percentage of the initial weight.

Part 2

Boneless leg (n = 100) and boneless shoulder roasts (n = 100) were randomly assigned to treatment combinations of a 2 x 5 factorial experiment. Roasts were cooked in a non-preheated or a preheated oven and were either fresh, frozen, thawed (12 h; 2loC), thawed (24 h; IOC) or thawed by microwave (OOC) prior to cooking. Thermocouples were placed in those roasts assigned to be frozen and then the roasts were individu- ally double-wrapped in freezer paper and frozen ( - 10OC). Ten leg and ten shoulder roasts in each treatment combinations were roasted with the fat side up on broiler racks and internal temperatures were monitored as described in Part 1. All roasts were cooked to an internal temperature of 7OOC.

The appliances used for cooking were Kenmore natural gas-range ovens (oven cavity: 62 x 39 x 46 cm). For microwave thawing of frozen roasts,


a counter top Litton microwave oven (115 v; 2,450 MHz; rated power input of 1,500 watts) was used. Roasts were thawed at the “Defrost” power level which was equivalent to 158 watts in output power as measured by the method of Decareau (Van Zante 1973).

Gas consumption was monitored using gas meters with a precision of 0.01 cu. ft. The electricity used to thaw roasts by microwaves was monitored by a digital counter with 0.1 kwh precision. The BTUs of purchased energy were calculated (lkwh=2413 BTU; 1 cu. ft. natural gas= 1031 BTU) according to Drew and Rhee (1978).

Cooking times and thawing times (microwave) were recorded. Cooking losses were calculated as the difference between initial and cooked weight as a percentage of initial weight. Shear force was obtained following a 2-4 h cooling period (after cooking) at room temperature (21OC). Each roast was trimmed of fat, heavy connective tissue and exterior browned surface. The maximum number of 1.27 cm cores possi- ble from each roast was obtained parallel to the orientation of the muscle fibers with a mechanical coring machine. Each core was sheared once by a Warner-Bratzler shear machine.

Table 1. Cooking t i m e ( m i d k g ) for l a m b roasts cooked” to dif ferent degrees of doneness.

Cooking t ime (min/kg)

Degree o f doneness

Rare Med i um We1 1 -done

Type o f roas t ( 60°C) (7OOC) (77°C)

Bone1 ess shoulder Pre-sl i c e d shoulders

Boneless l e g Whole, bone-in l e g

Shank-ha1 f l e g S i r l o i n - h a l f l e g Seven- r i b rack Crown r i b

71.37b 82.16b

66.27b 40.89b

73.29b 65.47b 68.13b 48.66b

87.37C 89.09b

83.51C

49.24C

94.09C 82.27C 88.23C

66.87C

95.21d

107.69C R6.06C

55.62d

109.694

109.16d 94 .u9c

73.84C

aBoneless shoulder; p r e - s l i c e d shoulder; boneless leg ; whole, bone-in leg; shank-half leg , and s i r l o i n - h a l f l e g cooked a t 163OC i n a non-preheated oven; seven-r ib rack and crown r i b roas ts cooked a t 191°C i n a non-preheated oven. n=10 f o r each r o a s t type cooked t o each degree o f doneness.

b*c,dMeans i n t h e same row w i t h a common s u p e r s c r i p t l e t t e r are not d i f f e r e n t (P>0.05).


Statistical Analyses

In the first study, analyses of variance were conducted to determine the effects of degree of doneness on cooking times and losses. In the second study, the main effects of oven temperature and roast treatment prior to cooking as well as the interaction effects on cooking times, cooking losses, energy consumption and shear force were determined by analyses of variance. Because no significant (P > 0.05) interactions were noted, main effect means were separated using Duncan's new multiple range test (Steel and Torrie 1980). All analyses were conducted using the Statistical Analysis System (SAS Institute, Inc. 1982).

RESULTS AND DISCUSSION

Cooking times (min/kg) for the eight roast types cooked to different degrees of doneness are presented in Table 1. In general, as the

Tab le 2. Percentage cooking loss for lamb roasts cooked" t o d i f ferent degrees of doneness.

Cooking l o s s (%) Degree o f doneness

Rare Med i urn We1 1 -done

Type o f r o a s t (60'C) (7OOC) (77'C)

Cooking l o s s (%) Degree o f doneness

Rare Med i urn We1 1 -done

Type o f r o a s t (60'C) (7OOC) (77'C)

Bone1 ess shoulder P r e - s l i c e d shoulder

Boneless l e g

Whole, hone- in l e g

Shank-ha1 f l e g S i r l o i n - h a l f l e g Seven-r i h rack

Crown r i b

23.04h 23.79b

21.37b

15.21h 15.28b 14.42b

iri.nnb

27.28C

28.78C

32.58C

22.79C 20.8lC 23.74C

19.08C

21.85C

35.01d 37.72d

33.95c

29.52d

24.254 32.29d 75.97d

28.n7d

aBoneless shoulder ; p r e - s l i c e d shoulder ; boneless l e g ; whole, bone-in l e g ; shank-hal f l e g ; and s i r l o i n - h a l f l e g r o a s t s cooked a t 163'C i n non-preheated ovens; s e v e n - r i b rack and crown r i b r o a s t s cooked a t 191°C i n non-preheated ovens. n=10 f o r each r o a s t t ype cooked t o each deyree o f doneness.

h,c.dMeans i n t h e same row w i t h a comnon s u p e r s c r i p t l e t t e r a re not d i f f e r e n t (P>0.05).

74 GRIFFIN, SAVELL, SMITH, RHEE AND J O H N S O N

internal temperatures of the roasts increased from rare to well-done, the cooking times increased. No difference was noted between rare and medium for presliced shoulders nor between medium and well-done for boneless leg, seven-rib rack or crown rib roasts. An average increase of 15.6 midkg was required to raise the internal temperature from 60 to 7OoC, while an average of 11.4 minikg was needed to raise the internal temperature from 70 to 77OC. Larger roasts required less time per kg than smaller roasts to reach the same internal temperature. Korschgen et aL (1980) reported cooking times of 96-114 midkg for 1.3-2.5 kg beef rib

Tab le 3. Recommended cooking t imes for lamb roasts*.

Reconended cook ing Degree o f t i m e

Type o f r o a s t donenessb (mi n / kg )

Leg, whole bone- in r a r e (3.2 t o 4.1 kg ) medi urn

we1 1 -done

33-44 44-55 55-66

Leg, bone1 ess (2.3 t o 3.2 kg)

Leg, shank-ha1 f (0.9 t o 1.8 kg)

Leg, s i r l o i n - h a 1 f (1.1 t o 2.3 kg )

r a r e 55-66 med i uin 66-77 we1 1 -done 77-88

r a r e 66-77 med i um 88-99 we1 1 -done 99- 110

r a r e 55-66

we1 1 -done 99- 110 medi urn 77-88

Shoulder, boneless r a r e 66-77 (1.9 t o 2.7 kg) medi um 77-88

we1 1 -done 88-99

Shoulder, p r e - s l i c e d r a r e (0.9 t o 2.3 kg)

Seven-r ib rack (0.7 t o 1.1 k g ) r a r e

medi um we1 1 -done

med i urn we1 1 -done

17-88 88-99 99-110

66-77 77-88 88-99

Crown r i b , n o t s t u f f e d r a r e 33-44 (0.9 t o 1.4 k g ) medi um 55-66

we1 1 -done 66-77

m e a n cook ing t i m e s were used t o determine recomnended cook ing t imes from n=lO f o r each r o a s t t y p e f o r each degree o f doneness. i n a non-preheated oven s e t a t 163°C except f o r seven- r i b rack and crown r i b r o a s t s where t h e oven s e t t i n g was 191'C.

A l l r o a s t s were cooked


roasts cooked to 7OoC in a preheated, electric oven (163OC). Data from this study (not in tabular form) indicate that similar weight lamb cuts required 66-99 midkg to reach 7OoC internally. Variations in time may be attributable to differing sizes and shapes of the roasts as well as whether or not roasts were boneless (Price and Schweigert 1971).

In Table 2, mean cooking losses are presented for various roasts cooked to each of the three degrees of doneness. Cooking losses varied considerably between roasts. However, for all roasts, cooking losses increased as the internal temperature increased from rare to medium to well-done. An average additional loss of 6.4% occurred when the internal temperature was increased from 60 to 7OoC while the average difference between 70 and 77OC was 6.2%. From these data, cooking loss increased 0.5% for every increase of one minute in cooking time which is half that reported for beef loin steaks (Hostetler et aL 1982).

From these data, recommendations for cooking time (midkg) were made using the mean and standard deviations for each lamb roast (Table 3). The differences in cooking time between roasts of different kinds are undoubtedly due to differences in shape, form, content of muscles, bone and fat as well as numbers of muscles per cut which results in differences in heat conductivity. In general, as roasts increased in weight, cooking times per kg decreased.

Table 4. Means" for cooking time, cooking loss, shear force value and gas consumption for boneless shoulders and boneless legs of lamb.

Bone1 ess shoulders Roneless 1 egs Non-preheated Pre-heated Non- p rehea t ed Preheated

oven oven oven oven Trait (11.50) (n=50) (n.50) (n=50)

Cooking time

Cooking loss

Shear force

Gas consumed

( m i n/kg) 95.2b 94.5b R3.2b 84.5b

( 4 6 ) 32.7b 32.2b 34.3b 34.6b

( k g ) 2.0b 2.0b 2.2b 2.2b

(cu. f t . ) 21.2b 2 2 . v 23.2b 24.3b

aMeans averaged across treatment groups; those means within the same roast type i n the same row with a comnon superscript letter are not different (P>0.05) .

76 GRIFFIN, SAVELL, SMITH, RHEE AND J O H N S O N

Part 2

Results of Part 2 of the study are presented in Tables 4-8. Because there were no significant interactions, the main effect means are shown. Cooking times, cooking losses, shear force values and gas consumption means by oven temperature and across roast treatment are illustrated in Table 4. There were no differences (P > 0.05) in cooking times, cooking losses or shear force values between non-preheated and preheated ovens for boneless shoulder or boneless leg roasts. The amount of gas used to roast boneless shoulders in preheated ovens was slightly higher (22.6 cu. ft.) than for those roasted in non-preheated ovens (21.2 cu. ft.). A similar trend for boneless leg roasts was observed but the means were not significantly different.

Mean cooking times by roast treatment across oven temperatures are shown in Table 5. Roasts in the fresh or thawed (microwave) treatment required the least amount of time to reach an internal temperature of 7OoC while shoulder and leg roasts in the frozen treatment required the greatest cooking times.

Mean percentage cooking losses (Table 6) followed a trend similar to that for cooking times. For boneless shoulders, those roasts cooked from the fresh and thawed (microwave) treatments had the lowest cooking losses while fresh boneless leg roasts had the lowest cooking losses.

In Table 7, mean shear force values are presented. Although some differences were detected, the magnitude of differences was small and all

Table 5. M e a n cooking t imes" during roast ing of boneless shoulders and boneless legs of lamb.

Cooking t ime (min/kg) Treatment Boneless shoulders Roneless legs

d

108.0b

80 .fit Thawed (24 h r ; 1OC) 100.8' 83.9'

d

Fresh 8^.!je 71.9

Frozen 111.1

Thawed (12 hr ; 2 loC) 9 1 .o

b

d

Thawed (microwave) 85 .8e 74.9

aMean cooking t imes (min/kg) averaged across non-preheated and pre-heated ovens; n-20 w i t h i n each r o a s t type and treatment group; f i n a l i n t e r n a l temperature 70°C (oven s e t t i n g 163OC).

b9csd*e*Means i n the same column w i t h a common superscr ip t l e t t e r are n o t d i f f e r e n t (P>0.05).


Tab le 6. M e a n percentage cooking losses" for boneless shoulders and boneless legs o f lamb.

Treatment Cooking l o s s (I)

Bone! ess shoulders Boneless l e g s

Fresh 29.gb 30.5b

Frozen 33.2' 3 5 2

Thawed (12 h r ; 21°C) 34.4c 3 5 2

Thawed (24 h r ; 1 O C )

Thawed (microwave)

33 .4c 35 .4c

35.4c b 31.5

'Means averaged across non-preheated and pre-heated ovens; n-20 w i t h i n each r o a s t t y p e and t rea tmen t group; f i n a l i n t e r n a l temperature 70°C (oven s e t t i n g 163OC).

bsCMeans i n t h e same column wi th a common s u p e r s c r i p t l e t t e r are n o t d i f f e r e n t (P>0.05).

Tab le 7. M e a n shear force valuesa fo r boneless shoulders and boneless legs o f lamb.

Treatment Shear f o r c e ( k g )

Boneless shoulders Boneless l e g s

Fresh 2.1b*c 2 .2c

Frozen 1.9d 2 . P

Thawed (12 hr ; 21'C) 2 .oc *d 2.1C

2 .oc d Thawed (24 h r ; 1'C) 1.8

Thawed (microwave) 2.2 b 2 .gb

aWarner-Bratz ler shear f o r c e (kg) necessary t o shear a 1.3 cm d iameter core; means averaged across non-preheated and pre-heated ovens; n.20 w i t h i n each r o a s t t y p e and t rea tmen t group; f i n a l i n t e r n a l t empera tu re 70'C (oven s e t t i n g 163OC).

b*csdMeans i n t h e same column w i t h a common s u p e r s c r i p t l e t t e r a r e n o t d i f f e r e n t (P>0.05).


Tab le 8. M e a n gas consumption" during r o a s t i n g (oven se t t i ng 163OC) of boneless shoulders and boneless legs of lamb.

Treatment Gas consumption (cu. f t . )

Boneless shoulders Boneless l e g s

Fresh

Frozen

Thawed (12 hr ; 21OC)

Thawed (24 h r ; 1°C)

Thawed (microwave)

~~

b 18.0d 23.2 b 2!1.8~ 24.6

23.6' 25.2b

23.4' 26 .Ob

18 .8~ 19.8' ~ ~~

'Mean gas consumption i n cu. ft.; means averaged across non-preheated and pre-heated ovens; n=20 w i t h i n each r o a s t t y p e and t rea tmen t group; f i n a l i n t e r n a l temperature 7OoC (oven s e t t i n g 163°C).

bsc*dMeans i n t h e same column w i t h a common s u p e r s c r i p t l e t t e r a re n o t d i f f e r e n t (P>0.05).

roasts were acceptable (Field et al. 1967) in tenderness. Roast treatments prior to cooking produced few practical differences in tenderness as indicated by shear force values.

Gas consumption means are shown in Table 8. Boneless shoulder roasts in the frozen treatment used the most gas while fresh shoulder roasts and those thawed by microwaves required the least gas. However, boneless leg roasts in the thawed (microwave) treatment required the least gas while no differences in the other four roast treatments were detected. If the total purchased energy is calculated (including BTU of electricity used for microwave thawing), then the total BTUs of purchased energy ranged from 18,558 to 26,800 with the least amount being used for fresh shoulder and leg roasts and the most BTUs used for frozen roasts. However, if the fuel cost is calculated ($O.O048/cu. ft. gas; $0.054/kwh electricity), then the cost range is $O.O86/kg to $0.123/kg to cook roasts treated as those in this study prior to cooking. Perhaps the total preparation time as well as the cooking losses are more important to the consumer than energy costs for cooking roasts from the fresh versus frozen or frozen and thawed state.

This study determined the average times necessary to cook various lamb roasts. Because the roast treatments and oven temperatures (non- preheated versus preheated) had minimal effects on energy costs of roasting, the effects of these variables on preparation time and cooking loss becomes more important in choosing a method most suitable for roasting lamb. Greater cooking losses were noted when roasts were cooked to higher degrees of doneness and when roasts were frozen rather than fresh prior to cooking.


ACKNOWLEDGMENTS

Technical article from the Texas Agricultural Experiment Station. This study was partially supported by the National Live Stock and Meat Board, Chicago, IL, the American Sheep Producer’s Council, Denver, CO and the Natural Fibers and Food Protein Commission of Texas, Dallas.

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