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Glossary of Biomass Terms 

Here you'll find definitions of commonly used biomass terms. 

A 

acid: A solution that has an excess of hydrogen ions (H+). 

acetic acid: An acid with the structure of C2H4O2. Acetyl groups are bound through an ester linkage to 

hemicellulose chains, especially xylans, in wood and other plants. The natural moisture present in plants 

hydrolyzes the acetyl groups to acetic acid, particularly at elevated temperatures. 

acid detergent fiber (ADF): Organic matter that is not solubilized after one hour of refluxing in an acid 

detergent of cetyltrimethylammonium bromide in 1N sulfuric acid. ADF includes cellulose and lignin. This 

analytical method is commonly used in the feed and fiber industries. (Source: Milne, T.A.; Brennan, A.H.; Glenn, 

B.H. Sourcebook of Methods of Analysis for Biomass Conversion and Biomass Conversion Processes. SERI/SP220-3548. Golden, CO: Solar Energy Research Institute, February 1990.) 

acid hydrolysis: The treatment of cellulosic, starch, or hemicellulosic materials using acid solutions (usually 

mineral acids) to break down the polysaccharides to simple sugars. 

acid insoluble lignin: Lignin is mostly insoluble in mineral acids, and therefore can be analyzed gravimetrically 

after hydrolyzing the cellulose and hemicellulose fractions of the biomass with sulfuric acid. ASTM E-1721-95 

describes the standard method for determining acid insoluble lignin in biomass. 

acid soluble lignin: A small fraction of the lignin in a biomass sample is solubilized during the hydrolysis process 

of the acid insoluble lignin method. This lignin fraction is referred to as acid soluble lignin and may be quantified 

by ultraviolet spectroscopy. (Source Ehrman, T. Determination of Acid-Soluble Lignin in Biomass. NREL-LAP-004. 

Golden, CO: National Renewable Energy Laboratory, September 9, 1996.) 

adsorption: The adhesion, in an extremely thin layer, of molecules (as in gases, solutions, or liquids) to the 

surface of solid bodies or liquids with which they are in contact. 

aerobic: Able to live, grow, or take place only where free oxygen is present. 

aerobic fermentation: Fermentation processes that require the presence of oxygen. 

agricultural residue: Agricultural crop residues are the plant parts, primarily stalks and leaves, not removed 

from the fields with the primary food or fiber product. Examples include corn stover (stalks, leaves, husks, and 

cobs); wheat straw; and rice straw. 

alcohol: An alcohol is an organic compound with a carbon bound to a hydroxyl group. Examples are methanol 

(CH3OH) and ethanol (CH3CH2OH). 

aldehyde: Any of a class of highly reactive organic chemical compounds characterized by the common group 

CHO and used in the manufacture of resins, dyes, and organic acids. 

aldoses: Occur when the carbonyl group of a monosaccharide is an aldehyde. (Source: Voet, D.; Voet, J. G. 

Biochemistry. New York: John Wiley, 1990.) 

algae: Simple photosynthetic plants containing chlorophyll, often fast growing and able to live in freshwater, 

seawater, or damp oils. May be unicellular and microscopic or very large, as in the giant kelps. 

alkali: Soluble mineral salt of alkali metals having characteristically “basic” properties. 

alkaline hydrolysis: The use of solutions of sodium hydroxide (or other alkali) in the treatment of cellulosic 

material (wood) to break down cellulose to simple sugars. 

alkali lignin: Lignin obtained by acidification of an alkaline extract of wood. 

amylase: Family of enzymes that act together to hydrolyze starch to individual glucose and dextran units. 

anaerobic: Living or active in an airless environment. 

anaerobic digestion: Degradation of organic matter by microbes in the absence of oxygen to produce methane 

and carbon dioxide. 

anhydrous: A material that does not contain water, either adsorbed on its surface or as water of crystallization. 

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annual: A plant that completes its life cycle in one year or less. 

aquatic plants: The aquatic biomass resources, such as algae, giant kelp, other seaweed, and water hyacinth. 

Certain microalgae can produce hydrogen and oxygen while others manufacture hydrocarbons and a host of other 

products. Microalgae examples include Chlorella, Dunaliella, and Euglena. 

arabinan: The polymer of arabinose with a repeating unit of C5H804. Can be hydrolyzed to arabinose. (Source: 

Voet, D.; Voet, J. G. Biochemistry. New York: John Wiley, 1990.) 

arabinose: A five-carbon sugar - C5H1005. A product of hydrolysis of arabinan found in the hemicellulose fraction 

of biomass. 

aromatic: A chemical that has a benzene ring in its molecular structure (benzene, toluene, xylene). Aromatic 

compounds have strong, characteristic odors. 

ash: Residue remaining after ignition of a sample determined by a definite prescribed procedure. (Source: 

Domalski, E.S.; Milne T.A., ed. Thermodynamic Data for Biomass Materials and Waste Components. The ASME 

Research Committee on Industrial and Municipal Wastes, New York: The American Society of Mechanical 

Engineers, 1987) 

attainment area: A geographic region where the concentration of a specific air pollutant does not exceed federal 

standards. 

auger: A rotating, screw-type device that moves material through a cylinder. In alcohol production, it is used to 

transfer grains from storage to the grinding site and from the grinding site to the cooker. 

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B 

B20: A mixture of 20% biodiesel and 80% petroleum diesel based on volume. 

bacteria: A small single-cell organism. Bacteria do not have an organized nucleus, but they do have a cell 

membrane and protective cell wall. Bacteria can be used to ferment sugars to ethanol. 

bagasse: Residue remaining after extracting a sugar-containing juice from plants like sugar cane. 

bark: The outer protective layer of a tree including the inner bark and the outer bark. The inner bark is a layer of 

living bark that separates the outer bark from the cambium and in a living tree is generally soft and moist. The 

outer bark is a layer of dead bark that forms the exterior surface of the tree stem. The outer bark is frequently 

dry and corky. (Source: Milne, T.A.; Brennan, A.H.; Glenn, B.H. Sourcebook of Methods of Analysis for Biomass 

Conversion and Biomass Conversion Processes. SERI/SP-220-3548. Golden, CO: Solar Energy Research Institute, 

February 1990.) 

barrel (of oil): A liquid measure equal to 42 U.S. gallons, or typically about 306 lb of oil. One barrel equals 5.6 

ft3; for crude oil, one barrel contains about 5.8 x 106 Btu of energy. 

base: A solution that has an excess of hydroxide ions (OH-

) in aqueous solution.

batch distillation: A process in which the liquid feed is placed in a single container and the entire volume is 

heated. 

batch fermentation: Fermentation conducted from start to finish in a single vessel without addition to or 

removal of a major substrate or product stream, respectively, until the process in complete. 

batch process: Unit operation where one cycle of feedstock preparation, cooking, fermentation, and distillation 

is completed before the next cycle is started. 

beer: A fermented broth that consists of water, ethanol, and small amounts of ether and assorted alcohols. 

benzene: An aromatic component of gasoline, which is a known cancer-causing agent. 

bioconversion: A general term describing the use of biological systems to transform one compound into 

another. Examples are digestion of organic wastes or sewage by microorganisms to produce methane and the 

synthesis of organic compounds from carbon dioxide and water by plants. 

biodiesel: A biodegradable transportation fuel for use in diesel engines. Biodiesel is produced through the 

transesterfication of organically-derived oils or fats. It may be used either as a replacement for or as a 

component of diesel fuel. 

bioenergy: The production, conversion, and use of material directly or indirectly produced by photosynthesis 

(including organic waste) to manufacture fuels and substitutes for petrochemical and other energy-intensive 

products. 

biofuels: Biomass converted to liquid or gaseous fuels such as ethanol, methanol, methane, and hydrogen. 

biogas: A gaseous mixture of carbon dioxide and methane produced by the anaerobic digestion of organic 

matter. 

biomass: Any plant-derived organic matter. Biomass available for energy on a sustainable basis includes 

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herbaceous and woody energy crops, agricultural food and feed crops, agricultural crop wastes and residues, 

wood wastes and residues, aquatic plants, and other waste materials including some municipal wastes. Biomass 

is a very heterogeneous and chemically complex renewable resource. 

biomass processing residues: Byproducts from processing all forms of biomass that have significant energy 

potential. For example, making solid wood products and pulp from logs produces bark, shavings and sawdust, 

and spent pulping liquors. Because these residues are already collected at the point of processing, they can be 

convenient and relatively inexpensive sources of biomass for energy. 

bone-dry-unit (BDU): 2400 lb of moisture-free wood, unless otherwise stated. 

British thermal unit (Btu): The amount of heat required to raise the temperature of one lb of water one degree 

Fahrenheit under one atmosphere of pressure and a temperature of 60-61 degrees Fahrenheit. 

by-product: Material, other than the principal product, generated as a consequence of an industrial process or 

as a breakdown product in a living system. 

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C 

cambium: The layer of reproducing cells between the inner bark (phloem) and the wood (xylem) of a tree that 

repeatedly subdivides to form new wood and bark cells. 

capacity: The maximum instantaneous output of an energy conversion device, often expressed in kW or MW. 

capital cost: The total investment needed to complete a project and bring it to an operable status. 

carbohydrate: Organic compounds made up of carbon, hydrogen, and oxygen and having approximately the 

formula (CH2O)n; includes cellulosics, starches, and sugars. (Source: Milne, T.A.; Brennan, A.H.; Glenn, B.H. 

Sourcebook of Methods of Analysis for Biomass Conversion and Biomass Conversion Processes. SERI/SP-220-

3548. Golden, CO: Solar Energy Research Institute, February 1990.) 

carbon dioxide: (CO2) A colorless, odorless gas produced by respiration and combustion of carbon-containing 

fuels. Plants use it as a food in the photosynthesis process. 

carbon monoxide: (CO) A colorless, odorless, poisonous gas produced by incomplete combustion. 

catalyst: A substance that increases the rate of a chemical reaction without being consumed or produced by the 

reaction. Enzymes are catalysts for many biochemical reactions. 

cellulase: A family of enzymes that break down cellulose into glucose molecules. 

cellulose: The carbohydrate that is the principal constituent of wood and other biomass and forms the structural 

framework of the wood cells. It is a polymer of glucose with a repeating unit of C6H10O5 strung together by ßglycosidic linkages. The ß-linkages in cellulose form linear chains that are highly stable and resistant to chemical 

attack because of the high degree of hydrogen bonding that can occur between chains of cellulose (see below). 

Hydrogen bonding between cellulose chains makes the polymers more rigid, inhibiting the flexing of the 

molecules that must occur in the hydrolytic breaking of the glycosidic linkages. Hydrolysis can reduce cellulose to 

a cellobiose repeating unit, C12H22O11, and ultimately to glucose, C6H12O6. Heating values for cellulose may be 

slightly different based upon the feedstock. Example values are shown below (higher heating value [HHV] at 30°

C, dry basis). (Source: Domalski, E.S.; Milne T.A., ed. Thermodynamic Data for Biomass Materials and Waste 

Components. The ASME Research Committee on Industrial and Municipal Wastes, New York: The American 

Society of Mechanical Engineers, 1987) 

cotton linters: HHV=7497 BTU/LB (4172.0 cal/g, 17426.4 J/g) 

wood pulp: HHV=7509.6 BTU/LB (4165.0 cal/g, 17455.6 J/g) 

Linear chains of glucose linked by b-Glycosidic bonds comprise cellulose 

chips: Small fragments of wood chopped or broken by mechanical equipment. Total tree chips include wood, 

bark, and foliage. Pulp chips or clean chips are free of bark and foliage. 

co-firing: The use of a mixture of two fuels within the same combustion chamber. 

co-generation: The technology of producing electric energy and another form of useful energy (usually thermal) 

for industrial, commercial, or domestic heating or cooling purposes through the sequential use of the energy 

source. 

combustion: A chemical reaction between a fuel and oxygen that produces heat (and usually, light). 

combustion air: The air fed to a fire to provide oxygen for combustion of fuel. 

continuous fermentation: A steady-state fermentation system in which substrate is continuously added to a 

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fermenter while products and residues are removed at a steady rate. 

coproducts: The resulting substances and materials that accompany the production of a fuel product such as 

ethanol. 

corn stover: The refuse of a corn crop after the grain is harvested. 

cracking: A reduction of molecular weight by breaking bonds, which may be done by thermal, catalytic, or 

hydrocracking. Heavy hydrocarbons, such as fuel oils, are broken up into lighter hydrocarbons such as gasoline. 

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D 

dehydration: The removal of a substantial portion of the water from any substance. 

dehydrogenation: The removal of hydrogen from a chemical compound. 

denaturant: A substance that makes ethanol unfit for consumption. 

dewatering: The separation of free water from the solids portion of spent mash, sludge, or whole stillage by 

screening, centrifuging, filter pressing, or other means. 

digester: A biochemical reactor in which anaerobic bacteria are used to decompose biomass or organic wastes 

into methane and carbon dioxide. 

disaccharides: The class of compound sugars that yields two monosaccharide units upon hydrolysis; examples 

are sucrose, maltose, and lactose. 

distillate: The portion of a liquid that is removed as vapor and condensed during a distillation process. 

distillation: The process by which the components of a liquid mixture are separated by boiling and recondensing 

the resultant vapors. The main components in the case of alcohol production are water and ethyl alcohol. 

distillers dried grains (DDG): The dried grain byproduct of the grain fermentation process, which may be used 

as a high-protein animal feed. 

drying: Moisture removal from biomass to improve serviceability and utility. 

dry ton: 2000 lb of biomass on a moisture-free basis. 

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E 

E-10: A mixture of 10% ethanol and 90% gasoline based on volume. 

E-85: A mixture of 85% ethanol and 15% gasoline based on volume. 

effluent: The liquid or gas discharged after processing activities, usually containing residues from such use. Also 

discharge from a chemical reactor. 

elemental analysis: The determination of carbon, hydrogen, nitrogen, oxygen, sulfur, chlorine, and ash in a 

sample. See ultimate analysis. 

energy crop: A crop grown specifically for its fuel value. These include food crops such as corn and sugar cane, 

and nonfood crops such as poplar trees and switchgrass. 

enzymatic hydrolysis: Use of an enzyme to promote the conversion, by reaction with water, of a complex 

substance into two or more smaller molecules. 

enzyme: A protein or protein-based molecule that speeds up chemical reactions occurring in living things. 

Enzymes act as catalysts for a single reaction, converting a specific set of reactants into specific products. 

ester: An ester is a compound formed from the reaction between an acid and an alcohol. In esters of carboxylic 

acids, the -COOH group of the acid and the -OH group of the alcohol lose water and become a -COO- linkage. 

ethanol: (CH3CH2OH) A colorless, flammable liquid produced by fermentation of sugars. Ethanol is used as a fuel 

oxygenate. Ethanol is the alcohol found in alcoholic beverages, but is denatured for fuel use. 

extractives: Any number of different compounds in biomass that are not an integral part of the cellular 

structure. The compounds can be extracted from wood by means of polar and non-polar solvents including hot or 

cold water, ether, benzene, methanol, or other solvents that do not degrade the biomass structure. The types of 

extractives found in biomass samples are entirely dependent upon the sample itself. (Source: Fengel, D.; Gerd, 

W. Wood Chemistry, Ultrastructure, and Reactions. Berlin-New York: Walter de Gruyter, 1989.) 

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F 

fast pyrolysis: Pyrolysis in which reaction times are short, resulting in higher yields of certain fuel products, 

which may range from primary oils to olefins and aromatics depending on the severity of conditions. 

fatty acid: A fatty acid is a carboxylic acid (an acid with a -COOH group) with long hydrocarbon side chains. 

feedstock: Any material used as a fuel directly or converted to another form of fuel or energy product. 

fermentation: A biochemical reaction that breaks down complex organic molecules (such as carbohydrates) into 

simpler materials (such as ethanol, carbon dioxide, and water). Bacteria or yeasts can ferment sugars to ethanol.

fixed bed: A bed of closely spaced particles through which gases move up or down for purposes of gasification or

combustion. 

fixed carbon: The carbon remaining after heating in a prescribed manner to decompose thermally unstable 

components and to distill volatiles. Part of the proximate analysis group. 

flash point: The temperature at which a combustible liquid will ignite when a flame is held over the liquid; 

anhydrous ethanol will flash at 51 degrees Fahrenheit. 

fluidized bed: A gasifier or combustor design in which feedstock particles are kept in suspension by a bed of 

solids kept in motion by a rising column of gas. The fluidized bed produces approximately isothermal conditions 

with high heat transfer between the particles and gases. 

fly ash: Small ash particles carried in suspension in combustion products. 

forestry residues: Includes tops, limbs, and other woody material not removed in forest harvesting operations 

in commercial hardwood and softwood stands, as well as woody material resulting from forest management 

operations such as pre-commercial thinnings and removal of dead and dying trees. 

fossil fuel: A carbon or hydrocarbon fuel formed in the ground from the remains of dead plants and animals. It 

takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels. 

fungi: Fungi are plant-like organisms with cells with distinct nuclei surrounded by nuclear membranes, incapable 

of photosynthesis. Fungi are decomposers of waste organisms and exist as yeast, mold, or mildew. 

furfural: An aldehyde derivative of certain biomass conversion processes; used as a solvent. 

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G 

galactan: The polymer of galactose with a repeating unit of C6H10O5. Found in hemicellulose it can be hydrolyzed 

to galactose. 

galactose: A six-carbon sugar with the formula C6H1206. A product of hydrolysis of galactan found in the 

hemicellulose fraction of biomass. 

gasification: Any chemical or heat process used to convert a feedstock to a gaseous fuel. 

gasifier: A device that converts solid fuel to gas. Generally refers to thermochemical processes. 

gas turbine: Sometimes called a combustion turbine; a gas turbine converts the energy of hot compressed 

gases (produced by burning fuel in compressed air) into mechanical power, which can be used to generate 

electricity. 

global warming: A term used to describe the increase in average global temperatures due to the greenhouse 

effect. 

glucan: The polymer of glucose with a repeating unit of C6H10O5. Cellulose is a form of glucan. Can be hydrolyzed 

to glucose. (Source: Voet, D.; Voet, J. G. Biochemistry. New York: John Wiley, 1990.) 

glucose: (C6H12O6) A simple six-carbon sugar. A product of the hydrolysis of glucan found in cellulose and starch. 

A sweet, colorless sugar that is the most common sugar in nature and the sugar most commonly fermented to 

ethanol. 

glycerin: (C3H8O3) A liquid by-product of biodiesel production. Glycerin is used in the manufacture of dynamite, 

cosmetics, liquid soaps, inks, and lubricants. 

greenhouse effect: The heat effect due to the trapping of the sun's radiant energy, so that it cannot be 

reradiated. In the earth's atmosphere, the radiant energy is trapped by greenhouse gases produced from both 

natural and human sources. 

greenhouse gas: A gas, such as water vapor, carbon dioxide, tropospheric ozone, methane, and low level 

ozone, which contributes to the greenhouse effect. 

grid: An electric utility’s system for distributing power. 

gross heat of combustion: see higher heating value 

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guaiacyl: A chemical component of lignin. It has a six-carbon aromatic ring with one methoxyl group attached. It 

is the predominant aromatic structure in softwood lignins. 

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H 

hardwood: One of the botanical groups of dicotyledonous trees that have broad leaves in contrast to the conifers 

or softwoods. The term has no reference to the actual hardness of the wood. The botanical name for hardwoods 

is angiosperms. Short-rotation, fast growing hardwood trees are being developed as future energy crops. 

Examples include: Hybrid poplars (Populus sp.), Hybrid willows (Salix sp.), Silver maple (Acer saccharinum), and 

Black locust (Robinia pseudoacacia). 

heating value: Higher heating value (HHV) is the potential combustion energy when water vapor from 

combustion is condensed to recover the latent heat of vaporization. Lower heating value (LHV) is the potential 

combustion energy when water vapor from combustion is not condensed. 

hemicellulose: Hemicellulose consists of short, highly branched chains of sugars. In contrast to cellulose, which 

is a polymer of only glucose, a hemicellulose is a polymer of five different sugars. It contains five-carbon sugars 

(usually D-xylose and L-arabinose) and six-carbon sugars (D-galactose, D-glucose, and D-mannose), and uronic 

acid. The sugars are highly substituted with acetic acid. The branched nature of hemicellulose renders it 

amorphous and relatively easy to hydrolyze to its constituent sugars compared to cellulose. When hydrolyzed, the 

hemicellulose from hardwoods releases products high in xylose (a five-carbon sugar). The hemicellulose 

contained in softwoods, by contrast, yields more six-carbon sugars. 

herbaceous plants: Non-woody species of vegetation, usually of low lignin content such as grasses. 

herbaceous energy crops: Perennial non-woody crops that are harvested annually, though they may take two 

to three years to reach full productivity. Examples include: Switchgrass (Panicum virgatum), Reed canarygrass 

(Phalaris arundinacea), Miscanthus (Miscanthus x giganteus), and Giant reed (Arundo donax). 

hexose: Any of various simple sugars that have six carbon atoms per molecule (e.g. glucose, mannose, and 

galactose.) 

higher heating value (HHV): The heat produced by combustion of one unit of substance at constant volume in 

an oxygen bomb calorimeter under specified conditions. The conditions are: initial oxygen pressure of 2.0-4.0 

MPa (20-40 atm), final temperature of 20°-35°C, products in the form of ash, liquid water, gaseous CO2 and N2, 

and dilute aqueous HCl and H2SO4. It is assumed that if significant quantities of metallic elements are combusted, 

they are converted to their oxides. In the case of materials such as coal, wood, or refuse, if small or trace 

amounts of metallic elements are present, they are unchanged during combustion and are part of the ash. Also 

known as gross heat of combustion. 

holocellulose: The total carbohydrate fraction of wood; cellulose plus hemicellulose. 

hybrid: The offspring of genetically different parents The term is applied as well to the progeny from matings 

within species and to those between species. Hybrids combine the characteristics of the parents or exhibit new 

ones. 

hydrocarbon: An organic compound that contains only hydrogen and carbon. In vehicle emissions, these are 

usually vapors created from incomplete combustion or from vaporization of liquid gasoline. Emissions of 

hydrocarbons contribute to ground level ozone. 

hydrocracking: A process in which hydrogen is added to organic molecules at high pressures and moderate 

temperatures; usually used as an adjunct to catalytic cracking. 

hydrogenation: Treatment of substances with hydrogen and suitable catalysts at high temperature and pressure 

to saturate double bonds. 

hydrolysis: The conversion, by reaction with water, of a complex substance into two or more smaller units, such 

as the conversion of cellulose into glucose sugar units. 

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I 

incremental energy costs: The cost of producing and/or transporting the next available unit of electrical energy 

above a previously determined base cost. 

inoculum: Microorganisms produced from a pure culture used to start a new culture in a larger vessel than that 

in which they were grown. 

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K 

Klason lignin: Lignin obtained from wood after the non-lignin components of the wood have been removed with 

a prescribed sulfuric acid treatment. A specific type of acid-insoluble lignin analysis. 

kraft process: Chemical pulping process in which lignin is dissolved by a solution of sodium hydroxide and 

sodium sulfide. 

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L 

landfill gas: Biogas produced from the natural degradation of organic material in landfills. 

lignin: The major non-carbohydrate, polypenolic structural constituent of wood and other native plant material 

that encrusts the cell walls and cements the cells together. It is a highly polymeric substance, with a complex, 

cross-linked, highly aromatic structure of molecular weight about 10,000 derived principally from coniferyl alcohol 

(C10H12O3) by extensive condensation polymerization. Higher heating value (oven dry basis): HHV=9111 BTU/LB 

(5062 CAL/G, 21178 J/G). (Source: Domalski, E.S.; Milne T.A., ed. Thermodynamic Data for Biomass Materials 

and Waste Components. The ASME Research Committee on Industrial and Municipal Wastes, New York: The 

American Society of Mechanical Engineers, 1987) 

lignin ratio of MeO to C9: Lignin empirical formulae are based on ratios of methoxy groups to phenylpropanoid 

groups (MeO:C9). The general empirical formula for lignin monomers is C9H10O2 (OCH3)n, where n is the ratio of 

MeO to C9 groups. Where no experimental ratios have been found, they are estimated as follows: 0.94 for 

softwoods; 1.18 for grasses; 1.4 for hardwoods. These are averages of the lignin ratios found in the literature. 

Paper products, which are produced primarily from softwoods, are estimated to have an MeO:C9 ratio of 0.94. 

lignin pseudo-molecule for modeling: The lignin ratio of methoxy groups to phenylpropanoid groups 

(MeO:C9) is used to calculate an ultimate analysis for the lignin pseudo-molecule. This ultimate analysis is used 

to estimate other properties of the molecule, such as its higher and lower heating values. 

lignocellulose: Refers to plant materials made up primarily of lignin, cellulose, and hemicellulose. 

lower heating value (LLV): The heat produced by combusting one unit of a substance, at atmospheric pressure 

under conditions such that all water in the products remains in the form of vapor. The net heat of combustion is 

calculated from the gross heat of combustion at 20°C by subtracting 572 cal/g (1030 Btu/lb) of water derived 

from one unit mass of sample, including both the water originally present as moisture and that formed by 

combustion. This subtracted amount is not equal to the latent heat of vaporization of water because the 

calculation also reduces the data from the gross value at constant volume to the net value at constant pressure. 

The appropriate factor for this reduction is 572 cal/g. (Source: Domalski, E.S.; Milne T.A., ed. Thermodynamic 

Data for Biomass Materials and Waste Components. The ASME Research Committee on Industrial and Municipal 

Wastes, New York: The American Society of Mechanical Engineers, 1987) 

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M 

mannan: The polymer of mannose with a repeating unit of C6H10O5. Can be hydrolyzed to mannose. (Source: 

Voet, D.; Voet, J. G. Biochemistry. New York: John Wiley, 1990.) 

mannose: (C6H1206) A six-carbon sugar. A product of hydrolysis of mannan found in the hemicellulose fraction of

biomass. 

mash: A mixture of grain and other ingredients with water to prepare wort for brewing operations. 

mass closure (%): The percent by weight of the total samples extracted from the biomass sample compared to 

the weight of the original sample. It is a sum of the weight percent of moisture, extractives, ash, protein, total 

lignin, acetic acid, uronic acids, arabinan, xylan, mannan, galactan, glucan, and starch. This is a good indicator of 

the accuracy of a complete biomass compositional analysis. 

metabolism: The sum of the physical and chemical processes involved in the maintenance of life and by which 

energy is made available to the organism. 

methane: (CH4) The major component of natural gas. It can be formed by anaerobic digestion of biomass or 

gasification of coal or biomass. 

methanol (wood alcohol): (CH3OH) An alcohol formed by catalytically combining carbon monoxide with 

hydrogen in a 1:2 ratio under high temperature and pressure. 

microorganism: Any microscopic organism such as yeast, bacteria, fungi, etc. 

moisture: The amount of water and other components present in the biomass sample that are volatilized at 105°

C. (Source: Ehrman, T. Standard Method for Determination of Total Solids in Biomass. NREL-LAP-001. Golden, 

CO: National Renewable Energy Laboratory, October 28, 1994.) 

moisture free basis: Biomass composition and chemical analysis data is typically reported on a moisture free or 

dry weight basis. Moisture (and some volatile matter) is removed prior to analytical testing by heating the sample 

at 105°C to constant weight. By definition, samples dried in this manner are considered moisture free. 

monosaccharide: A simple sugar such as a five-carbon sugar (xylose, arabinose) or six-carbon sugar (glucose, 

fructose). Sucrose, on the other hand is a disaccharide, composed of a combination of two simple sugar units, 

glucose and fructose. 

municipal solid waste: Any organic matter, including sewage, industrial, and commercial wastes, from 

municipal waste collection systems. Municipal waste does not include agricultural and wood wastes or residues. 

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N 

native lignin: The lignin as it exists in the lignocellulosic complex before separation. 

net heat of combustion: see lower heating value 

neutral detergent fiber: Organic matter that is not solubilized after one hour of refluxing in a neutral detergent 

consisting of sodium lauryl sulfate and EDTA at pH 7. NDF includes hemicellulose, cellulose, and lignin. (Source: 

Milne, T.A.; Brennan, A.H.; Glenn, B.H. Sourcebook of Methods of Analysis for Biomass Conversion and Biomass 

Conversion Processes. SERI/SP-220-3548. Golden, CO: Solar Energy Research Institute, February 1990.) 

nitrogen oxides: (NOx) A product of photochemical reactions of nitric oxide in ambient air, and the major 

component of photochemical smog. 

non-renewable resource: A non-renewable energy resource is one that cannot be replaced as it is used. 

Although fossil fuels, like coal and oil, are in fact fossilized biomass resources, they form at such a slow rate that, 

in practice, they are non-renewable. 

NREL: The National Renewable Energy Laboratory. 

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O 

octane rating (octane number): A measure of a fuel’s resistance to self ignition, hence a measure as well of 

the antiknock properties of the fuel. Diesel fuel has a low octane rating, while gasoline and alcohol have high 

octane ratings suitable for spark-ignition engines. 

organic compound: An organic compound contains carbon chemically bound to hydrogen. Organic compounds 

often contain other elements (particularly O, N, halogens, or S). 

oven dry ton: An amount of wood that weighs 2000 lb at 0% moisture content. 

oxygenate: An oxygenate is a compound which contains oxygen in its molecular structure. Ethanol and biodiesel

act as oxygenates when they are blended with conventional fuels. Oxygenated fuel improves combustion 

efficiency and reduces tailpipe emissions of CO. 

ozone: A compound that is formed when oxygen and other compounds react in sunlight. In the upper 

atmosphere, ozone protects the earth from the sun's ultraviolet rays. Though beneficial in the upper atmosphere, 

at ground level, ozone is called photochemical smog, and is a respiratory irritant and considered a pollutant. 

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P 

particulates: A fine liquid or solid particle such as dust, smoke, mist, fumes, or smog, found in air or emissions. 

petroleum: Any petroleum-based substance composed of a complex blend of hydrocarbons derived from crude 

oil, including motor fuel, jet oil, lubricants, petroleum solvents, and used oil. 

phloem: In plants, the inner bark; the principal tissue in a tree concerned with the transport of sugars and other 

nutrients from the leaves. 

photoconversion: Conversion of light into other forms of energy by chemical, biological, or physical processes. 

photosynthesis: A process used by many plants and bacteria to build carbohydrates from carbon dioxide and 

water, using energy derived from light. Photosynthesis is the key initial step in the growth of biomass and is 

depicted by the equation: CO2 + H2O + light + chlorophyll = (CH2O) + O2. 

polymer: A large molecule made by linking smaller molecules (monomers) together. 

polysaccharide: A long-chain carbohydrate containing at least three molecules of simple anhydrous sugars 

linked together. Examples include cellulose and starch. 

process development unit: An experimental facility that establishes proof of concept, preliminary process 

economics, and engineering feasibility for a pilot or demonstration plant. 

process heat: Energy, usually in the form of hot air or steam, needed in the manufacturing operations of an 

industrial plant. 

proof: The ethanol content of a liquid at 60 degrees Fahrenheit stated as twice the percent by volume of the 

ethyl alcohol. 

proximate analysis: The determination, by prescribed methods, of moisture, volatile matter, fixed carbon (by 

difference), and ash. The term proximate analysis does not include determinations of chemical elements or 

determinations other than those named. The group of analyses is defined in ASTM D 3172. 

protein: A protein molecule is a chain of up to several hundred amino acids and is folded into a more or less 

compact structure. Because about 20 different amino acids are used by living matter in making proteins, the 

variety of protein types is enormous. In their biologically active states, proteins function as catalysts in 

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metabolism and to some extent as structural elements of cells and tissues. Protein content in biomass (in mass 

%) can be estimated by multiplying the mass % nitrogen of the sample by 6.25. (Source: Biofuels Glossary. 

September 1986. Solar Technical Information Program, Solar Energy Research Institute.) 

pyrolysis: The breaking apart of complex molecules by heating in the absence of oxygen, producing solid, liquid, 

and gaseous fuels. 

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R 

reaction: A chemical reaction is a dissociation, recombination, or rearrangement of atoms. 

recombinant DNA: DNA that has been artificially introduced into a cell, resulting in alteration of the genotype 

and phenotype of the cell, and is replicated along with natural DNA. Used in industrial micro-organisms to 

produce more productive strains. 

renewable energy resource: An energy resource that can be replaced as it is used. Renewable energy 

resources include solar, wind, geothermal, hydro, and biomass. Municipal solid waste (MSW) is also considered to 

be a renewable energy resource. 

residues, biomass: Byproducts from processing all forms of biomass that have significant energy potential. For 

example, making solid wood products and pulp from logs produces bark, shavings and sawdust, and spent 

pulping liquors. Because these residues are already collected at the point of processing, they can be convenient 

and relatively inexpensive sources of biomass for energy. 

ROI: Return on investment. 

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S 

saccharide: A simple sugar or a more complex compound that can be hydrolyzed to simple sugar units. 

saccharification: A conversion process using acids, bases, or enzymes in which long-chain carbohydrates are 

broken down into their component fermentable sugars. 

screen analysis: Method for measuring a proportion of variously sized particles in solid fuels. The sample is 

passed through a series of screens of known size openings. Biomass fuel screen sizes usually range from 5 to 100 

openings per inch. 

scrubber: An air pollution control device that uses a liquid or solid to remove pollutants from a gas stream by 

adsorption or chemical reaction. 

slow pyrolysis: Thermal conversion of biomass to fuel by slow heating to less that 842 degrees Fahrenheit (450 

degrees Celsius) in the absence of oxygen. 

softwood: Generally, one of the botanical groups of trees that in most cases have needle-like or scale-like 

leaves; the conifers; also the wood produced by such trees. The term has no reference to the actual hardness of 

the wood. The botanical name for softwoods is gymnosperms. 

starch: A molecule composed of long chains of a-glucose molecules linked together (repeating unit C12H16O5 ). 

These linkages occur in chains of a-1,4 linkages with branches formed as a result of a-1,6 linkages (see below). 

This polysaccharide is widely distributed in the vegetable kingdom and is stored in all grains and tubers. A not-soobvious consequence of the a-linkages in starch is that this polymer is highly amorphous, making it more readily 

attacked by human and animal enzyme systems and broken down into glucose. Gross heat of combustion: Qv

(gross)=7560 Btu/lb (4200 cal/g,17570 J/g). (Source: Domalski, E.S.; Milne T.A., ed. Thermodynamic Data for 

Biomass Materials and Waste Components. The ASME Research Committee on Industrial and Municipal Wastes, 

New York: The American Society of Mechanical Engineers, 1987) 

The polymeric structure of glucose in starch tends to be amorphous 

steam turbine: A device for converting energy of high-pressure steam produced in a boiler into mechanical 

power. This power can then be used to generate electricity. 

stover: The dried stalks and leaves of a crop remaining after the grain has been harvested. 

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structural chemical analysis: The composition of biomass reported by the proportions of the major structural 

components; cellulose, hemicellulose, and lignin. 

substrate: The base on which an organism lives or a substance acts upon (as by an enzyme). 

syringyl: A component of lignin, normally only found in hardwood lignins. It has a six-carbon aromatic ring with 

two methoxyl groups attached. 

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T 

tar: A liquid product of thermal processing of carbonaceous materials. 

thermochemical conversion: The use of heat to change substances chemically to produce energy products. 

total lignin: The sum of the acid soluble lignin and acid insoluble lignin fractions. 

total solids: The amount of solids remaining after all volatile matter has been removed from a biomass sample 

by heating at 105°C to constant weight. (Source: Ehrman, T. Standard Method for Determination of Total Solids 

in Biomass. NREL-LAP-001. Golden, CO: National Renewable Energy Laboratory, October 28, 1994.) 

toxics: As defined in the 1990 Clean Air Act Amendments, toxics include benzene, 1,3 butadiene, formaldehyde, 

acetaldehyde, and polycyclic organic matter. 

transesterification: A chemical process which reacts an alcohol with the triglycerides contained in vegetable oils 

and animal fats to produce biodiesel and glycerin. 

triglyceride: A triglyceride is an ester of glycerol and three fatty acids. Most animal fats are composed primarily 

of triglycerides. 

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U 

ultimate analysis: The determination of the elemental composition of the organic portion of carbonaceous 

materials, as well as the total ash and moisture. See elemental analysis. (Source: Milne, T.A.; Brennan, A.H.; 

Glenn, B.H. Sourcebook of Methods of Analysis for Biomass Conversion and Biomass Conversion Processes. 

SERI/SP-220-3548. Golden, CO: Solar Energy Research Institute, February 1990.) 

uronic acid: A simple sugar whose terminal -CH2OH group has been oxidized to an acid, COOH group. The uronic 

acids occur as branching groups bonded to hemicelluloses such as xylan. (Source: Milne, T.A.; Brennan, A.H.; 

Glenn, B.H. Sourcebook of Methods of Analysis for Biomass Conversion and Biomass Conversion Processes. 

SERI/SP-220-3548. Golden, CO: Solar Energy Research Institute, February 1990.) 

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V 

vacuum distillation: The separation of two or more liquids under reduced vapor pressure; reduces the boiling 

points of the liquids being separated. 

volatile: A solid or liquid material that easily vaporizes. 

volatile matter: Those products, exclusive of moisture, given off by a material as a gas or vapor, determined by 

definite prescribed methods that may vary according to the nature of the material. One definition of volatile 

matter is part of the proximate analysis group usually determined as described in ASTM D 3175. (Source: Milne, 

T.A.; Brennan, A.H.; Glenn, B.H. Sourcebook of Methods of Analysis for Biomass Conversion and Biomass 

Conversion Processes. SERI/SP-220-3548. Golden, CO: Solar Energy Research Institute, February 1990.) 

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W 

wet scrubber: An air pollution control device used to remove pollutants by bringing a gas stream into contact 

with a liquid. 

whole tree chips: Wood chips produced by chipping whole trees, usually in the forest. Thus the chips contain 

both bark and wood. They are frequently produced from the low-quality trees or from tops, limbs, and other 

logging residues. 

willstatter lignin: Lignin obtained from the lignocellulosic complex after it has been extracted with hydrochloric 

acid. 

wood: A solid lignocellulosic material naturally produced in trees and some shrubs, made of up to 40%-50% 

cellulose, 20%-30% hemicellulose, and 20% -30% lignin. 

wort: The liquid remaining from a brewing mash preparation following the filtration of fermentable beer. 

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X 

xylan: A polymer of xylose with a repeating unit of C5H804, found in the hemicellulose fraction of biomass. Can 

be hydrolyzed to xylose. Gross heat of combustion: Qv(gross)=17751.9 Jg-1. (Source: Domalski, E.S.; Milne 

T.A., ed. Thermodynamic Data for Biomass Materials and Waste Components. The ASME Research Committee on 

Industrial and Municipal Wastes, New York: The American Society of Mechanical Engineers, 1987) 

xylose: (C5H10O5) A five-carbon sugar. A product of hydrolysis of xylan found in the hemicellulose fraction of 

biomass. 

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Y 

yeast: Any of various single-cell fungi capable of fermenting carbohydrates. 

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