Journal of
Archaeological
SCIENCE
Journal of Archaeological Science 30 (2003) 1077–1084
http://www.elsevier.com/locate/jas
Small fragments make small differences in efficiency when rendering
grease from fractured artiodactyl bones by boiling
Robert R. Church, R. Lee Lyman *
Department of Anthropology, 107 Swallow Hall, University of Missouri, Columbia, MO 65211, USA
Received 6 August 2002; received in revised form 20 December 2002; accepted 8 January 2003
Abstract
Part of the conventional wisdom of modern zooarchaeology is that in order for grease to be efficiently rendered from bones by
boiling, skeletal elements must be broken into very small pieces. Experimental boiling of fresh long bones (humeri, femora, tibiae)
of white-tailed deer (Odocoileus virginianus) reduced to various sizes indicates this is not necessarily true. No significant difference
was found in the efficiency (rate) of rendering grease from bone fragments generated by hammerstone breakage (fragment maximum
dimension %5 cm) or from bones cut into pieces of 4, 2, or 1 cm maximum dimension. All produced over 80% of their renderable
grease in 2–3 h of boiling. Long bones cut into three pieces comprising the complete diaphysis and two epiphyses were the least
efficiently boiled; 80% of their grease was rendered in 5 h. The small amount of grease rendered suggests that the extraction of
fat-soluble trace nutrients other than lipids may be an additional reason that bone fragments were boiled.
2003 Elsevier Science Ltd. All rights reserved.
Keywords: Bone grease; Grease rendering; Bone fragment size; Bone boiling; Efficiency
1. Introduction
The belief that sets of numerous small fragments of
bone found within archaeological contexts are indicators
of the rendering, by boiling, of bone grease may have
originated in North America with Peale [21], who
described the extraction of marrow and grease by various North American Indian peoples. This seminal
account received later support from Leechman’s [10]
description of the rendering of bone grease from caribou
(Rangifer tarandus) and moose (Alces alces) long bones
by Canadian people. Zierhut [30] and Bonnichsen [3]
echoed Leechman’s descriptions when they documented
the grease-rendering methods used by the Calling Lake
Cree. Vehik [27] reviewed and summarized ethnographic
literature, e.g. Refs. [26,28] regarding bone fracturing
and grease rendering by Plains people. She observed that
“bone grease and/or soup seemed to be the only reason
that bone was finely crushed” and that “bone was
* Corresponding author. Tel.: +1-573-882-9850; fax: +1-573-8845450
E-mail address: [email protected] (R.L. Lyman).
broken into small pieces primarily to obtain grease” [27,
p. 169]. At the same time, Binford [2, pp. 157–163] and
Yellen [29, pp. 291–293] published ethnoarchaeological
data on bone fragmentation and grease rendering that
seemed to confirm earlier observations. As a result,
intensively and extensively fragmented bone [13], perhaps with an abundance of associated fire-cracked rock
and less often an associated pit or hearth-like feature,
effectively became the taphonomic signature of bonegrease rendering. This interpretive algorithm today
forms a part of zooarchaeology’s conventional wisdom,
e.g. Refs. [4–8,11,19,20,23,25].
The reasoning underpinning the interpretive algorithm is that grease is efficiently extracted by boiling if
the bone fragments are small. Peale [21, p. 391] stated
that bones to be boiled for grease rendering are “broken
into small fragments” and “comminuted”; Leechman
[10, p. 355] and Zierhut [30, p. 35] used virtually
identical wording. Probably because of these and later
observations by others, it is thought that grease is
extracted most efficiently from small fragments because
of the greater surface area to volume ratio of small
pieces relative to that ratio as evidenced by large pieces.
0305-4403/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0305-4403(03)00010-4
1078
R.R. Church, R.L. Lyman / Journal of Archaeological Science 30 (2003) 1077–1084
Ignoring for the moment the question of how small
‘small’ fragments are, this key notion is often implicit in
the literature. Speth and Spielmann [25, p. 19], for
example, indicate that hunter-gatherers “smash” bones
and then boil “the small pieces of bones in water until
the grease is extracted”. The key notion that grease is
most efficiently rendered from small fragments is apparent in Brink’s [4, p. 260] excellent, if brief, description of
grease rendering: “Recovery of [bone grease, which
literally impregnates bone tissue] requires smashing
bones into small fragments, cooking bone chips in
heated water for an extended period of time, and
skimming fat off the surface of the water” (emphasis
added). The key notion is explicit in Lupo and Schmitt’s
[12, p. 143] statement that “bones are broken into small
pieces to facilitate grease extraction” (emphasis added).
Although the key notion that grease is more efficiently rendered from small fragments of bone than
from large fragments makes sense intuitively, we are
unaware of empirical research substantiating it. It is
perhaps for this reason that the size of small fragments is
seldom reported in explicit terms. Leechman’s [10,
p. 355] Native American informant indicated that bones
were broken into pieces “as big as finger nails” prior to
boiling. Vehik [27, p. 176] reported that most of the
archaeological specimens she believed had been boiled
“were smaller than 2 cm2”. Chomko and Gilbert [6,
p. 681] indicated that the fragments of archaeological
bone they studied had a “mean size range of 5–7 cm,”
which we assume reflects the maximum dimension of the
pieces. Fragments in an ethnoarchaeological context
that Yellen [29, pp. 302–303] measured averaged about
8 cm in length. Apparently, it is believed by some that
the size of small fragments may vary taxonomically;
Smith and McNees [23] report archaeological data indicating most specimens of bison (Bison bison) were
3–6 cm long whereas most specimens of pronghorn
antelope (Antilocapra americana) were %3 cm long.
Virtually all researchers who have written about the
topic indicate that bones must be broken into small
fragments if grease is to be rendered from them by
boiling. The literature cited in this paragraph indicates
that ‘small’ may be as small as 1 cm2 or as large as
7–8 cm in maximum dimension. We return to this issue
later and here simply note that the literature we cited
here served as a guide when we designed our research.
In this paper we describe our efforts to determine
experimentally if small fragments are better than large
fragments in terms of the efficiency of extracting grease
by boiling, and to determine how small ‘small’ fragments
must be. We also suggest that the traditional explanation that bone boiling was geared toward grease
rendering because of the lipid (fat) content of the grease
[12,27] may be only part of the explanation given the
relatively small returns relative to the costs of production. The grease rendered may have provided critically
Table 1
Frequencies of processed bones by skeletal element and experimental
lot
Lot
Humerus Femur Tibia
1.
2.
3.
4.
5.
10
9
10
10
10
11
11
10
10
11
12
12
11
11
12
33
32
31
31
33
49
53
58
160
Hammerstone broken
Diaphysis and epiphysis
4 cm
2 cm
1 cm
Total
Total
important trace nutrients as well as caloric energy in the
form of lipids.
2. Materials and methods
Based on her extensive review of the ethnographic
literature for North America, Vehik [27, p. 172] concluded that “long bone ends seem generally not to have
been used in making bone grease”, something apparent
in Zierhut’s [30] terse description as well. However,
literature that we examined and some references Vehik
cites suggest long-bone ends were in fact boiled for
grease extraction. Some analysts have therefore broken
epiphyseal ends as well as diaphyses of long bones
during experimental rendering of grease, e.g. Refs.
[5,12]. In his experiments, Brink [5] rendered most grease
from the proximal and distal ends of long bones;
he extracted relatively little grease from diaphysis
fragments. We followed the lead of others in our
experiments and boiled all portions of long bones.
We obtained fresh, complete humeri, femora, and
tibiae of white-tailed deer (Odocoileus virginianus) from
butchers during the annual autumn deer season in
Missouri. Healthy, non-pathological skeletal specimens
of adult size were chosen; in all cases epiphyses were
fully fused or nearly so. Specimens of each skeletal
element were divided into five lots of approximately
equal numbers of each skeletal element (Table 1). As
much soft tissue (muscle, fat, etc.) as possible was
removed manually with a sharp knife. For all bones in
all lots, upon reduction of an individual skeletal element
(=complete anatomical unit) into pieces, all marrow was
removed manually so that only bone fragments were
boiled. We did not manually remove soft tissue trapped
in the trabecular-bone tissue of the ends (epiphyses) of
long bones.
Lot 1 bones were laid on a basalt anvil stone and
broken with a granite hammerstone into pieces %5 cm
in maximum dimension to simulate prehistoric conditions. Lot 2 bones were cut with a saw into three
pieces—the two epiphyseal ends and the diaphysis. Cuts
were made at the approximate location of the metaphyseal suture, and the three pieces were boiled. Lot 3
R.R. Church, R.L. Lyman / Journal of Archaeological Science 30 (2003) 1077–1084
1079
Table 2
Descriptive data for the average cumulative proportion of grease extracted for each hour in each lot of bones
Hours boiled
Lot 1 (Broken)
Lot 2 (Diaph and Epiph)
Lot 3 (4 cm)
Lot 4 (2 cm)
Lot 5 (1 cm)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
48.56
76.40
83.42
89.79
90.97
92.21
95.07
97.51
98.31
99.24
99.78
99.90
100.00
100.00
29.05
42.06
57.94
72.89
83.40
90.41
92.98
99.06
99.29
99.35
99.46
99.89
99.95
100.00
41.41
72.66
89.22
92.05
93.78
94.65
95.99
97.81
98.01
99.04
99.64
99.87
100.00
100.00
56.53
79.45
85.56
90.78
92.76
94.89
95.78
97.02
98.25
99.02
99.79
100.00
100.00
100.00
63.31
80.13
87.13
91.26
94.06
95.52
96.22
97.23
98.24
99.25
99.57
100.00
100.00
100.00
bones were cut into pieces 4 cm in maximum dimension.
Diaphysis pieces were 4 cm long and comprised the
complete circumference of the diaphysis; similarly, epiphyses were cut into pieces with a maximum dimension
of 4 cm. Lot 4 bones were cut into pieces 2 cm in
maximum dimension. Diaphysis pieces were then cut in
half parallel to the long axis of the bone such that half
the circumference of the diaphysis was represented by
each piece. Lot 5 bones were cut into 1 cm long segments, then each diaphysis piece was cut in quarters
parallel to the long axis of the bone such that each piece
comprised one fourth of the diameter of the diaphysis.
During all stages of reduction, all adhering soft tissue
and marrow was removed manually, but again, none
was removed from trabecular bone. All pieces of each
individual skeletal element were boiled independently of
all other skeletal elements in a lot.
For all lots, bone pieces resulting from reduction were
rinsed to remove bone dust, marrow, and other residue,
and were then dried. Each set of fragments comprising a
skeletal element in each lot was then placed in a
stainless-steel wire basket and placed in boiling water in
a stainless-steel pot. After each hour of boiling, the wire
basket and fragments were removed, and the water–
grease mixture was poured from the pot into a separation flask. The pot was rinsed of all residue into the
separation flask. Water was subsequently drained, and
the remaining grease was measured to the nearest 0.5 ml.
The boiling procedure was then repeated with the bone
fragments for another hour, the water–grease solution
separated, and the grease measured. This protocol was
repeated until bone pieces no longer produced measurable oils or grease, and then was done one more time to
ensure there was no more extractable grease or oil.
For purposes of this study, efficiency is defined in
terms of the time necessary to extract all grease and
oil from a set of bone fragments. The less the requisite
boiling time, the greater the efficiency of grease
extraction. This definition is possible because all but one
of the several other experimental variables were held
constant. The taxon used, the skeletal elements used in
each lot, the boiling protocol followed, the temperature
of the boiling water, and the heat source were constant
across all boiling events. The only variable that differed
was the size of the bone fragments that were boiled.
Because we are interested in part in comparing the
efficiency of grease extraction across sets of bone fragments of different size, irrespective of the amount of
grease extracted, we use cumulative frequency distribution curves to display the average rate of grease
extraction from each lot irrespective of skeletal elements
within the lots. We presume that a rapid rate of grease
extraction is more efficient than a slow rate.
Kolmogorov–Smirnov two-sample D statistics are used
to assess whether differences in rate and efficiency are
statistically significant.
3. Results
3.1. Small fragments make small differences
Descriptive data on the average cumulative proportion of grease extracted per hour of boiling for each lot
are summarized in Table 2 and graphed in Fig. 1. These
data suggest several things. First, as might be expected
given conventional wisdom, grease was rendered more
slowly—and thus less efficiently—from the Lot 2 specimens (diaphysis and epiphyses) than from the specimens
comprising any other lot. Lot 2 specimens produced
80% of their grease after 5 h of boiling whereas all other
lots, comprising smaller specimens, produced 80% of
their grease after 2–3 h of boiling. Statistically, the Lot 2
specimens are not significantly less efficient than the Lot
3 specimens of 4 cm maximum dimension, but they are
significantly less efficient than the Lot 4 specimens of
2 cm maximum dimension, the Lot 5 specimens of 1 cm
1080
R.R. Church, R.L. Lyman / Journal of Archaeological Science 30 (2003) 1077–1084
Table 4
Absolute amount of grease (ml) rendered per lot after 1 h of boiling
Lot 1
Mean 4.41
SD
1.31
Range 2.04–7.54
Fig. 1. Cumulative frequency curves of average proportion of grease
extracted per bone per hour of boiling for each lot of bones. Data from
Table 2.
Table 3
Kolmogorov–Smirnov two-sample D statistics between pairs of bone
lots
Lot
1
2
3
4
2
D=0.3434
p<0.05
Hour 2
D=0.0715
p>0.05
Hour 1
D=0.0797
p>0.05
Hour 1
D=0.1475
p>0.05
Hour 1
D=0.3128
p>0.05
Hour 3
D=0.3739
p<0.05
Hour 2
D=0.3807
p<0.05
Hour 1
D=0.1512
p>0.05
Hour 1
D=0.2190
p>0.05
Hour 1
D=0.0678
p>0.05
Hour 1
3
4
5
Lot 1, hammerstone broken; Lot 2, diaphysis and epiphyses; Lot
3, 4 cm; Lot 4, 2 cm; and Lot 5, 1 cm. ‘Hour’ is total elapsed time of
boiling when difference between lots is greatest.
maximum dimension, and the Lot 1 specimens produced
by a hammerstone and anvil (Table 3).
More interestingly, although the tendency is for
grease to be rendered more quickly as fragment size
decreases across Lots 3, 4, and 5 (Fig. 1), not one of
these lots is significantly different statistically from any
other one in terms of efficiency (Table 3). That is,
whether specimens are 4, 2, or 1 cm they have a statistically insignificant influence on the efficiency of grease
rendering. Fig. 1, however, suggests just what conventional wisdom predicts. After 1 h of boiling, the 1-cm
fragments (Lot 5) have produced 63% of their grease, the
2-cm fragments (Lot 4) have produced 56%, the 4-cm
fragments (Lot 3) 41%, and the hammerstone broken
fragments (Lot 1) have produced 48%. We believe Lot 1
produced more grease during the first hour than Lot 3
because the former comprised many fragments <4 cm
maximum dimension.
Lot 2
Lot 3
Lot 4
Lot 5
2.74
0.73
1.95–4.35
4.01
0.82
2.49–6.41
5.47
0.56
4.22–6.46
5.76
0.65
4.23–6.87
The notable difference between Lots 3 (4 cm), 4
(2 cm), and 5 (1 cm) and the Lot 1 specimens is evident
after 1 h of boiling (Fig. 1), but it is statistically insignificant (Table 3). That statistic is, however, based on
the cumulative proportion of grease extracted. The
absolute abundance of grease produced per lot after 1 h
of boiling suggests something else (Table 4). First, note
that the mean amount of grease rendered increases from
a low in Lot 2 (epiphyses–diaphysis) to Lot 3 (4 cm), to
Lot 1 (hammerstone broken), to Lot 4 (2 cm), to Lot 5
(1 cm). This is what conventional wisdom predicts.
Second, the mean amount of grease rendered per bone in
Lot 2 is significantly lower than the mean of any other
lot (Student’s t>6.3, p<0.0001 for all). The mean amount
of grease per bone produced in Lot 1 is not statistically
different from the mean of Lot 3 (t⫽1.47, p⫽0.14), but it
is significantly less than the means for Lots 4 and 5
(t>4.1, p<0.0001 for both). Finally, the means for Lots 4
and 5 are only weakly significantly different (t⫽1.86,
p⫽0.07).
Another interesting aspect of our results is that,
irrespective of fragment size, between 70 and 80% of all
grease was rendered after 2 h of boiling, and after 3 h
between 85 and 90% of the grease in specimens comprising Lots 3, 4, and 5 was extracted. These data suggest
not only that boiling for no more than 2–3 h would be
sufficient in most cases, but that long bones need to be
broken into pieces smaller than complete diaphyses and
epiphyses, perhaps %5 cm maximum dimension, to be
relatively efficiently boiled for grease extraction. There is
no evidence in our data suggesting that ‘finely crushed’
[27, p. 169] or ‘pulverized’ [2, p. 158; 23, p. 81] bone is
required. Further, as we noted above, the available
ethnoarchaeological data indicate that bone fragments
that were boiled ranged between 1 and 8 cm maximum
dimension.
Three important observations emerge at this point.
First, small fragments do make a difference in terms of
efficiency of grease rendering by boiling, but those
differences are small. Second, there seems to be little
reason to boil bone fragments beyond an hour or two.
Third, our experiments indicate that the requisite size of
‘small’ pieces is %5 cm maximum dimension. None of
these observations requires a change in the conventional
wisdom of zooarchaeology, but we suggest that they do
require that our conventional wisdom be qualified.
R.R. Church, R.L. Lyman / Journal of Archaeological Science 30 (2003) 1077–1084
1081
Table 5
Efficiency of grease extraction from different skeletal elements of the
hammerstone broken lot
Hours boiled
Femur
Humerus
Tibia
1
2
3
4
5
6
7
8
9
10
11
12
13
14
No of elements
47.15
78.47
84.75
90.35
91.20
92.36
94.78
96.76
97.21
98.62
99.67
99.83
100
100
11
46.66
72.64
82.86
90.12
91.40
92.38
95.19
97.09
98.57
99.41
99.83
99.93
100
100
10
51.62
77.29
82.48
88.92
90.38
91.90
95.29
98.64
99.26
99.75
99.86
99.94
100
100
12
Mean of grease extracted (ml)
SD of grease extracted (ml)
Range of grease extracted (ml)
10.04
8.57
8.65
2.35
2.05
1.43
6.74–14.65 6.15–12.12 6.65–11.74
Fig. 2. Cumulative frequency curves of average proportion of grease
extracted per skeletal element per hour of boiling for hammerstone
broken Lot 1 bones. Data from Table 5.
Table 6
Descriptive statistics for amount (ml) of grease extracted per bone
per lot
3.2. Different skeletal elements make no difference
We used the same three skeletal elements in each lot,
but we wondered if there might be some difference
between the lots given the slight differences in frequencies of each skeletal element included in each lot. To
determine if the skeletal elements included might be
influencing the differences in efficiency across lots, we
compared the efficiency of grease rendering from each
skeletal element within hammerstone broken Lot 1.
Descriptive data are given in Table 5 and are graphed in
Fig. 2. There is no statistically significant difference
between the efficiency of extracting grease from any
single skeletal element over either of the other two
skeletal elements (p>0.1 for all pairs). Further, we note
that the average amount of grease extracted from any
one skeletal element is not significantly different from
the average amount of grease extracted from either of
the other two skeletal elements (Student’s t<1.7,
p>0.09 for all pairs). In fact, any one lot is no different
from any other lot in terms of efficiency of extracting
grease from particular skeletal elements, just as might be
expected from Table 3.
3.3. Amounts of grease
Recalling that marrow was removed manually prior
to boiling, it is important to note that, on average, any
single bone in any given lot of bones produces little
grease (Table 6). If the left and right humeri, left and
right femora, and left and right tibiae from an average
animal were boiled, about 28–29 ml of grease would be
produced. We found that 1 ml of wet grease weighs
Lot
Mean Standard
deviation
No of
bones
Range
Coefficient of
variation
1
2
3
4
5
9.09
9.39
9.68
9.68
9.09
33
32
31
31
33
6.15–14.65
7.39–12.39
7.40–12.58
7.20–11.59
6.81–10.73
22.22
15.34
12.81
10.33
10.56
2.02
1.44
1.24
1.00
0.96
1.25 g; the standard measure of energy yield for dry
marrow fat of deer is 9.37 kcal/g [15]. Using these two
conversion factors to calculate energy yield of bone
grease, 35–36 g of grease representing about 330–
335 kcal would be produced by a pair of average humeri,
femora, and tibiae. Madrigal and Capaldo [14] found
that the same set of bone pairs (two humeri, two femora,
two tibiae) from white-tailed deer would, on average,
produce about 614 kcal from the marrow grease. Even
realizing that the energy yield we calculated for bone
grease is only approximate, we have to wonder why
anyone would break deer bones into small pieces to
extract grease by boiling?1
A possible explanation for the small size of bone
pieces is suggested by the variation in the average
amount of grease extracted per bone. Considering only
Lots 2–5, as bone fragment size decreases, the coefficient
of variation in the amount of grease extracted per bone
1
Extracting grease from bones of larger animals such as bison or
moose would probably produce more grease, but we suspect that the
cost of extracting that grease—energy to break bones, fuel to heat
water, etc.—would also be greater. We do not know if the increased
costs and increased benefits would cancel each other out.
1082
R.R. Church, R.L. Lyman / Journal of Archaeological Science 30 (2003) 1077–1084
Table 7
Descriptive statistics for amount (ml) of grease extracted per skeletal
element per lot
Lot
Humerus
Femur
Tibia
1. Mean
Standard deviation
Range
Coefficient of variation
8.57
2.05
6.15–12.12
23.92
10.04
2.35
6.74–14.65
23.41
8.65
1.43
6.65–11.74
16.53
2. Mean
Standard deviation
Range
Coefficient of variation
10.20
1.61
7.75–12.39
15.78
9.09
1.40
7.39–12.22
15.40
9.06
1.19
7.72–11.87
13.13
3. Mean
Standard deviation
Range
Coefficient of variation
9.59
1.28
7.40–11.37
13.35
9.80
1.41
7.74–12.58
14.39
9.65
1.16
8.29–11.64
12.02
4. Mean
Standard deviation
Range
Coefficient of variation
9.50
0.93
8.19–10.97
9.79
9.82
1.32
7.20–11.59
13.44
9.71
0.76
8.27–10.94
7.83
5. Mean
Standard deviation
Range
Coefficient of variation
9.26
0.98
7.21–10.73
10.58
8.72
1.10
6.81–10.72
12.61
9.29
0.77
8.00–10.41
8.29
also decreases (Table 6). This reduction in variation also
occurs across each of the three individual skeletal elements included in the lots (Table 7). These data suggest
that small fragments more consistently have most of
their grease efficiently rendered than do large fragments.
Perhaps this is why small fragments rather than large
ones are ethnoarchaeologically documented when grease
is rendered by boiling, but it leaves unattended the
question of why someone would boil bones to render
grease. We turn to that question next.
4. Discussion
We extracted small amounts of grease from any given
bone in any given lot. This begs a question: Why, given
these seemingly miniscule returns, would anyone boil
bone fragments in the first place? The grease might be
considered an ‘unearned resource’ if (i) the animal were
procured mainly for other resources such as meat, hides,
sinew, and bone, and (ii) bones were broken for marrow
extraction, thereby reducing the cost of breaking them
for grease extraction. Speth and Spielmann [25, p. 19]
state that rendering bone grease by boiling is “labor
intensive,” but the cost of building and maintaining
a fire for several hours to extract most (ca. 80%; Fig. 1)
of the grease from a set of bone fragments is unknown.
Lupo and Schmitt’s [12] experimental data and
Binford’s [2] ethnoarchaeological data indicate that the
cost of grease rendering by boiling is high relative to the
amount of grease collected. Binford [2, p. 159] indicates
“7 oz” of grease was obtained from an unknown number
of long-bone ends after 110 min of “almost continuous
activity” of two women, not including the time required
to cut and gather firewood. We initially suspected that
one would obtain more fat from marrow, at less cost,
than were one to boil bone fragments to render grease.
McCullough and Ullrey [15] found, however, that of the
total fat in white-tailed deer, an average of 2.3% occurs
in the marrow whereas an average of 4% occurs in bone
tissue. Perhaps our suspicion is wrong, but to determine
this we need data we do not have on the cost of
extracting marrow and the cost of extracting grease by
boiling bone fragments.
Lipids and fats (carbohydrates) are critical to a
nutritious diet [4,25]. Lupo and Schmitt [12] suggest that
“cooking” bone fragments with meat—either loose or
still adhering to the bone pieces—enhances the nutritional quality of lean meat because the grease rendered
from the bone tissue permeates the meat, see also Ref.
[29]. But is the fat in extracted grease the reason to boil
bones? Vehik [27, p. 172] was the first to note that the
fatty lipids of bone grease are a source of “vitamins A,
D, E, and K and can exert a thiamine, protein, and liver
glycogen sparing action [1, pp. 203–204]”. This point
seems to have largely been overlooked by subsequent
researchers. Speth [24, p. 330], for example, merely
noted that “fatty foods carry important fat-soluble
vitamins” as he and other researchers came to focus on
lipids as an energy source provided by grease. We
suspect the latter resources are where an additional,
seldom acknowledged benefit of grease rendered by
boiling of bone fragments resides. Roberts et al. [22]
found that boiling of bone tissue not only renders the
grease (collagen) but it decreases the nitrogen content of
the tissue. Our preliminary research indicates that nitrogen, calcium, phosphorus, and magnesium are all
depleted in boiled bone. Some portion of these elements
may be dissolved in the water and another portion in the
grease. Grease rendered from bones by boiling thus
contains not just calories in the form of lipids, which
may be a small benefit by itself, but also trace nutrients
in the form of vitamins and minerals.
Fat is differentially distributed throughout the body
of a white-tailed deer. McCullough and Ullrey [15,
p. 436] found that, on average, 69% of the total fat was
in “separable adipose deposits, 19% was in muscle tissue,
and 6.9% in viscera.” This distribution may cause one to
wonder why marrow fat and bone grease would be
pursued, given that together they make up a mere 6–7%
of total body fat. The reason that bones are broken open
for marrow and that bone fragments are boiled to
extract grease is related to the physiology of deer and
many other animals. As documented by biologists
(cited in Ref. [17]), subcutaneous fact is mobilized first,
then intermuscular fat, intramuscular fat is third, body
R.R. Church, R.L. Lyman / Journal of Archaeological Science 30 (2003) 1077–1084
cavity fats fourth, and finally marrow fat. The last is
metabolized beginning with proximal limb elements and
ending with distal limb elements. It is unknown whether
fats in interstitial spaces of bone tissue are eventually
mobilized [4]. Ungulates in northern areas with seasonal
climates are good sources of fat during the fall but their
value is low during season(s) when they are under
nutritional stress. Bone boiling for purposes of grease
extraction could be a potential indicator of season of
resource use [4,11], if it can be recognized taphonomically, which it may not be [21]. But more important in
the context of this paper is the potential that, as Brink
[4] has suggested, grease within the interstitial spaces of
bone tissue may be the last tissue that is depleted of fats,
and we would add non-lipid trace nutrients, when the
animal is under nutritional stress. Such nutrients include
fat-soluble vitamins, essential fatty acids, and trace
minerals such as iron and calcium [18]. Fatty acids are
particularly important with respect to growth, development, and overall nutrition [9,16]. Thus bone boiling
may be an important way to obtain otherwise scarce or
hard to procure nutrients.
5. Conclusions
We have not explored the non-lipid avenue further as
yet, because our experiment was originally designed to
test one small part of the conventional wisdom of
zooarchaeology. That wisdom holds that in order to
extract grease efficiently—defined as minimum boiling
time—from artiodactyl bones those bones must be
broken into very small pieces; they must be pulverized.
Our experiments confirm this but to an unexpectedly
limited degree. On the one hand, simply breaking a long
bone into two ends and the shaft would not result in
efficient extraction of grease because 5 h of boiling are
required to extract 80% of the grease. In terms of the
total grease that might be extracted from bones, there is
no statistical difference in efficiency if long bones are
broken into pieces of 5, 4, 2, or 1 cm in maximum
dimension. The average amount of grease extracted
during the first hour of boiling, on the other hand, is
greatest for the smallest fragments. Further, variation in
the amount of grease rendered decreases as fragment
size decreases, and this may be part of the reason why
bone fragments to be boiled are broken into small
pieces. But our data align with ethnoarchaeological data
and indicate that bones need not be pulverized in order
that their grease be efficiently rendered by boiling. Our
data indicate that about 80% of the extractable grease
can be rendered in 2–3 h from fragments %5 cm maximum dimension. We conclude that small fragments
make small differences in the rate or efficiency of grease
extraction. An important question that remains concerns whether or not the fat in extracted grease is the
only resource being pursued.
1083
Acknowledgements
We thank M.J. O’Brien for comments on an early
draft, and K. Ames for encouragement. J. Brink and
J.D. Speth provided particularly insightful and helpful
comments that prompted us to reconsider several key
issues.
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