Bulk Density

Bulk density is defined as weight of fiber per unit volume, often expressed as gmL−1, and is a good index of structural changes (Sreerama et al., 2009).

From: Pulse Foods (Second Edition), 2021

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Food Powder Properties

Alex López-Córdoba, Silvia Goyanes, in Reference Module in Food Science, 2017

Bulk Density and Porosity

Bulk density is the mass of bulk solid that occupies a unit volume of a bed, including the volume of all interparticles voids. Taking into account that a powder is really a particle gas mixture with both interparticle spaces and intraparticle voids (Fitzpatrick et al., 2013), three classes of bulk density have become conventional: aerated, poured, and tap. Each of these depends on the treatment to which the sample is subjected.

Aerated bulk density is when the volume of the powder is at a maximum, caused by aeration, just prior to complete breakup of the bulk.

Poured bulk density is when the volume is measured after pouring powder into a cylinder, creating a relatively loose structure.

Tapped bulk density is, in theory, the maximum bulk density that can be achieved without deformation of the particles. In practice, it is generally unrealistic to attain this theoretical tapped bulk density, and a lower value obtained after tapping the sample in a standard manner is used.

Porosity indicates the volume fraction of void space or air space inside a material. Volume determination is relative to the amount of internal (or closed) or external (or open) pores present in the powder. Porosity is directly related to bulk density (Eq. 2):

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Milk Powder

S.D. Kalyankar, ... S.S. Deosarkar, in Encyclopedia of Food and Health, 2016


Bulk density is a very complex product property for MP and is of great importance for economical and functional reasons. High bulk density is desirable for reducing shipping and packaging costs. On the other hand, low bulk density, as seen in agglomerated products, influences other powder properties such as flowability and instant characteristics. Bulk density is the weight of a volume unit of powder and is usually expressed in g/cm3, kg/m3, or g/100 ml. Bulk density is usually determined by measuring the volume of 100 g of powder in a 250 ml graduated cylinder after exposure to compaction by standardized tapping. The bulk density of nonfat dry milk has a wide range, from 0.18 to 1.25 g ml 1. Regular spray-dried nonfat dry milk is approximately 0.50–0.60 g ml 1, while roller-dried nonfat dry milk is 0.30–0.50 g ml 1. The bulk density of the final powder is a result of particle density (occluded air and density of the solids) and the interstitial air. Bulk density can be influenced by many different factors, which include density of the solids, amount of air entrapped in the particles (occluded air) or the particle density, and amount of interstitial air (air between the particles). Occluded air is one of the most important factors for controlling bulk density.

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Compost feedstocks

Authors:Robert RynkMary SchwarzContributors:Tom L. RichardMatthew CottonThomas HalbachStefanie Siebert, in The Composting Handbook, 2022

3.4 Bulk density

Bulk density, the mass or weight per unit volume, is a good general index of the quality of a feedstock for composting, with 600 kg/m3 (1000 lbs/yd3) being a good target. Bulk density reflects the feedstock's moisture content, porosity, free air space (FAS), and aeration capabilities (see Chapter 3). The bulk density (like porosity and FAS) of a mixture of feedstocks cannot be predicted with accuracy from individual ingredients because particles of different feedstocks intermingle.1 For instance, the small particles of a dense feedstock fill the voids spaces within a bulky one. Hence, one cannot simply take a weighted average of two feedstocks to calculate the bulk density of their mixture. Still, in sufficient proportions, feedstocks with a low bulk density generally lower the bulk density of a mix and thus improve aeration.

The bulk density of a given feedstock can be highly variable, depending on moisture and its tendency to settle and compact. The compacted material at the bottom of a pile is denser than the material near the top. In addition to the overbearing weight, small particles tend to settle toward the base. The moist material at the center has a higher bulk density than the drier material near the surface. Hence, accurately quantifying the bulk density requires good sampling technique. If the moisture content of a particular feedstock varies considerably, it can be characterized by its dry bulk density (wet bulk density x dry matter content).

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Wetland Soils: Physical and Chemical Properties and Biogeochemical Processes

Courtney Mobilian, Christopher B. Craft, in Reference Module in Earth Systems and Environmental Sciences, 2021

Bulk density and porosity

Bulk density is the mass of dry soil per unit volume, typically expressed as g cm 3. The proportion of mineral versus organic particles, to a large extent, determine bulk density. Organic soils have much lower bulk density compared to mineral soils (Table 1). In organic soils, bulk density ranges from about 0.1 g cm 3 for Fibrists to 0.2–0.3 g cm 3 for Hemists and Saprists. In wetland mineral soils, bulk density ranges from 0.5–1.5 g cm 3.

Porosity is the volume of soil that is filled with either water or air. It is inversely related to bulk density; as bulk density increases, porosity decreases. Soil texture is an important determinant of porosity. Porosity of mineral soils is often around 50% for both sandy and clayey soils. However, the pores of sandy soils are large (macropores) whereas clayey soils have smaller pores (micropores). The macropores of sands promote air and water movement but limits their water holding capacity. Clays, because of their micropores, have excellent water holding capacity but poor air and water movement and, hence poor drainage. Organic soils, because of their low bulk density, tend to have much higher porosity compared to mineral soils (Table 1). The pore space of wetland soils is often filled with water, in contrast to upland soils where the pores are filled with air most of the time.

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Analysis of rice quality

Kshirod R. Bhattacharya, in Rice Quality, 2013

Bulk density

Bulk density (or density in a mass) is the weight of the material including the intergranular air space in unit volume. This is determined with the help of the test weight apparatus (Fig. 13.12). The container comes in a litre or 500 ml capacity. The grains are allowed to fall into the container from a standard height at a standard flow rate through the funnel. The heap above the container is then levelled with zigzag strokes of the blunt ruler. The grain inside the container is then weighed. The bulk density is expressed in grams/litre.

Fig. 13.12. Test weight apparatus.

Photo: courtesy, K. Sabeena

As explained in Chapter 2, the bulk density of a grain is unrelated to its size (grain weight) but is related to its shape. The more slender the grain (higher the L/B or L/T ratio), the less the bulk density. Paddy has much lower bulk density than milled rice, mainly because of the air space inside the husk.

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Legume fiber characterization, functionality, and process effects

Uma Tiwari, Enda Cummins, in Pulse Foods (Second Edition), 2021

7.4.1 Bulk density

Bulk density is defined as weight of fiber per unit volume, often expressed as g mL−1, and is a good index of structural changes (Sreerama et al., 2009). The common method of estimating bulk density of fibers is by placing a known quantity (2 g) of fiber into a graduated syringe and applying sufficient pressure to pack the content in the syringe while recording the final volume (Parott and Thrall, 1978). Chau and Cheung (1999) investigated the effects of the IDFs prepared from Phaseolus angularis, Phaseolus calcaratus, and Dolichos lablab seeds relative to cellulose on control of cholesterol absorption in hamsters. They observed that the bulk density of Dolichos lablab insoluble fiber was significantly (P < .05) higher, whereas the bulk densities of all three insoluble fibers were lower than that of the cellulose (Table 7.4). Further, a linear correlation was identified between HDL:total cholesterol ratio and the bulk density (r = -0.99, P < .05) from the three legume insoluble fibers (Chau and Cheng, 1999). Dalgetty and Baik (2003) concluded that hull and soluble fibers contain higher densities of soluble fiber than insoluble fibers. The bulk density of pea hull and insoluble and soluble fibers were shown to have 0.75, 0.21, and 0.80 g mL−1, respectively. They also noted that the lentils hull and insoluble fibers have the highest bulk density with 0.81 and 0.21 g mL−1, respectively, whilst chickpeas soluble fiber was the densest of the soluble fibers with 0.83 g mL−1. Huang et al. (2009) demonstrated that smaller fiber particles are shown to have a higher bulk density and may lower the ability of the fiber to absorb water and oil. They observed a higher bulk density of 0.64 g mL−1 for mung bean hulls with particle size of <50 mesh, whereas a lower bulk density of 0.45 g mL−1 was observed with a particle size >0.35 g mL−1. In a study, Du et al. (2014) investigated the bulk densities of the various legumes (pinto bean, lima bean, red kidney bean, black bean, navy bean, small red bean, black eye bean, mung bean, lentil, and chickpea). They concluded that the bulk density varied from 0.543 g mL−1 (lentil) to 0.816 g mL−1 (black bean), respectively, indicating higher density of lentils compared to other legumes. Therefore, understanding the bulk density of legumes is important for formulation of foods, including weaning foods.

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Volume 5

Geoffrey W. Smithers, in Encyclopedia of Dairy Sciences (Third Edition), 2022

Bulk Density

Bulk density is regarded as the weight per unit volume and is expressed as kg m−3, and it is a very important property, both from a cost and marketing perspective. Bulk density is currently determined by measuring the volume of 100 g of powder in a 250 mL−1 graduated glass cylinder. The bulk density of milk powders is a very complex property because it is the result of many powder characteristics and is influenced by several processing factors such as feed composition and concentration, feed temperature and foamability, milk preheating, age thickening, type of atomizer, particle temperature history, and particle size distribution, as depicted in Fig. 9.

Fig. 9. Interrelationship of various drying parameters and physical-chemical characteristics.

Adapted from Pisecky (2012) and Masters (2002).

Nozzle atomization results in powder with a higher bulk density than centrifugal atomization. The manufacturing procedure and conditions influence bulk density, primarily because of the effects of occluded air (see below). Consequently, steps to reduce occluded air increase density. Minimizing the air content of the concentrate before drying, increasing the total solids of the concentrate (a higher concentration can be used with centrifugal atomization), reducing the spray pressure, or using a large orifice are examples of processing steps to reduce occluded air. In addition, less uniformity in particle size distribution results in closer packing and a higher bulk density. The shape and the size of the particles also affect the bulk density of powder particles.

The relatively low density of milk powders has several practical implications. It is undesirable as it leads to higher packaging, storage, and transportation costs. By adding certain non-dairy ingredients such as sucrose or additives to milk before drying, the bulk density of the dry product will be affected more and less depending on the true density of each ingredient.

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Volume 2

Ruohui Lin, ... Cordelia Selomulya, in Encyclopedia of Dairy Sciences (Third Edition), 2022

Bulk Density

The bulk density of the powder (Dbulk) contained the density of the particle and the interstitial air (air trapped between the particles). The volume of interstitial air depends on particle packing arrangements, which is significantly affected by various levels of vibrations subject to the powders. The difficulty defining interstitial air leads no universally agreed method to determine the bulk density. In spite of many arguments, the IDF method might be commonly recognized (ISO/IDF, 2005b), providing clear definitions of poured, loose, and bulk density, as shown in Fig. 3. 100 g of powder in a 250 mL measuring cylinder is tapped at room temperature. After 0, 100 and 625 times of taps manually or using apparatus with tap function, the poured bulk density, the loose bulk density, and the bulk density of powders are calculated based on their recorded volumes of the powder, respectively. The particle size distribution, the particle shape, and the degree of agglomeration all determine the amount of interstitial air (Kelly and Fox, 2016), and therefore further influence the results of the bulk density. For example, wider size distribution of non-agglomerated powders would result in higher interstitial air and further lead to lower bulk density.

Figure 3. Demonstration of poured bulk, loose and bulk density based on IDF standard (ISO/IDF, 2005b).

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Particle, Powder, and Compact Characterization

G.E. Amidon, ... D.M. Mudie, in Developing Solid Oral Dosage Forms (Second Edition), 2017 Bulk density

Bulk density is the mass per unit volume of a loose powder bed. The unit volume includes the spaces between the particles, and the envelope volumes of the particles themselves. The method used to fill the material into that volume can affect the degree to which the powder is compressed and can thus influence the bulk density value.14,15 Bulk density can be calculated using Eq. (10.2), where M=mass in grams and Vo=untapped apparent volume in milliliters.


The loose or “aerated” bulk density can be determined by allowing a defined amount of material to fill a container with a known volume under the influence of gravity.16 The amount to which the particles collapse and fill voids between the particles depends on some powder properties, including particle shape, PSD, interparticle friction, and cohesion.

Bulk density is typically measured by gently introducing a known sample mass into a graduated cylinder, and carefully leveling the powder without compacting it. The apparent untapped volume is then read to the nearest graduated unit. As most pharmaceutical powders have densities in the range of 0.1–0.7 g/mL, a 25-mL graduated cylinder filled at least 60% full calls for a sample mass of approximately 2–11 g. (Since this test is nondestructive, the material may be reused.) USP requirements dictate a minimum graduated cylinder size of 25 mL.16 However, if a material is in short supply, a 10-mL graduated cylinder may be used. Although wall effects could be observed, this approach provides a reasonable estimate of the bulk density.

Bulk density is an essential parameter for process development and solid dosage manufacturing. It is used in determining the amount of powder that can fit in a space such as a blender or a hopper on a tablet press or capsule filler. It is also used to determine the amount of powder that can be fitted into a capsule. Previous work has suggested that the effective bulk density of the same material will vary under different dynamics.14,15

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The composting process

Authors:Cary OshinsFrederick MichelContributors:Pierce LouisTom L. RichardRobert Rynk, in The Composting Handbook, 2022

4.7 Bulk density

Bulk density is the mass or weight per unit volume of an accumulation of particulate materials.2 For instance, bulk density applies to a pile of wood chips while a single wood chip is characterized by particle density or simply density. In the realm of composting, bulk density is commonly expressed in kilograms per cubic meter (kg/m3) and pounds per cubic yard (lbs/yd3).

Bulk density is perhaps the best single index of how well a mix of feedstocks aerates because it is influenced by several relevant factors—moisture content, porosity, particle size, and the density of the individual particles. It increases with higher moisture and with lower porosity. Therefore, it also reflects the FAS in a composting material. As the straight lines in Fig. 3.18 suggest, bulk density correlates very well with porosity and FAS. In short, bulk density provides an overall indication for the physical and aeration conditions of a composting mass. Furthermore, it is easily measured in the field. Thus, bulk density serves as a good gauge for combining feedstocks and managing the composting process.

Figure 3.18. Correlation of bulk density with free air space (FAS) and porosity for paper-mill deinking sludge.

Adapted from Day and Shaw (2001).

As a rule of thumb for most composting feedstocks, the starting bulk density of a feedstock mix should be lower than 700 kg/m3 (1200 lbs/yd3), and preferably below 600 kg/m3 (roughly 1000 lbs/yd3). Above 600 kg/m3, aeration becomes increasingly difficult, and beyond 700 kg/m3 it nearly stops. If the bulk density is very low (below 400 kg/m3 or about 700 lbs/yd3), the material may be so porous that heat escapes quickly and the temperatures fail to reach the desired level. Alternatively, the low temperature might be due to abundance slowly decomposing large, woody, or dry feedstocks responsible for the low bulk density. In either case, this problem is rare and can be overcome by building larger piles.

One problem with using bulk density as a management criterion is that it differs throughout a pile or windrow. Because of compression, bulk density increases from the top to the base of a pile. Thus, bigger (taller) piles tend to have a greater overall bulk density and are more difficult to effectively aerate. When the bulk density of a standing pile is measured, samples must be taken at different depths in the pile or at a depth known to represent the average condition. A large difference in bulk density from top to bottom can be corrected by turning, at least temporarily. Methods used to measure bulk density should account for changes in bulk density as samples are removed from the pile. A standard method for field measurement of bulk density is presented in Chapter 4.

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