Caballero B. (ed.) Encyclopaedia of Food Science, Food Technology and Nutrition. Ten-Volume Set

Подождите немного. Документ загружается.

may also occur during distillation and maturation.

Saturated and unsaturated chains are found, ranging

from one to 16 carbon atoms. Short-chain alcohols

such as propanols, butanols, and pentanols are the

most abundant. Nonaliphatic alcohols include 2-

phenylethanol and 2,3-butanediol. The principal or-

ganic acid is acetic acid, accounting for between 50

and 90% of the total content of volatile acids. Octa-

noic, decanoic, and dodecanoic acids are quantita-

tively important, though lower-molecular-weight

acids such as butanoic and pentanoic acids may

have more sensory impact. The most abundant esters

are the ethyl esters of the acids named, their concen-

trations reflecting the relative abundance of the acid.

Any other combination of the acids and alcohols

present may occur. After ethyl esters, the most abun-

dant are acetate esters such as isoamyl acetate and

phenylethyl acetate. The esters of hydroxy acids, such

as lactic acid, and of dicarboxylic acids, such as suc-

cinic acid, can be distilled along with alcohol and

steam and so occur in whisky.

Aliphatic Carbonyl Compounds

0007The majority of carbonyl compounds are produced

by the metabolic actions of the yeast. However, their

formation by oxidation of unsaturated fatty acids or

Strecker degradations has been shown to occur at

almost any stage of production. Acetaldehyde is the

most common and is often used to determine total

aldehydic content. Many other aldehydes, ketones,

and acetals have also been identified. For aldehydes

andketones,aliphaticchainlengths,bothsaturatedand

unsaturated, range from two to 14 carbon atoms.

Due to the high alcoholic strengths of the distillate,

G. Woody

H. Sweet

. Stale

. Sulfury

. Cheesy

. Oily

. Primary taste

. Peaty

. Grainy

. Grassy

. Fruity

. Floral

. Feints

1. stagnant

2. metallic

1. cardboard

4. woody

3. floral

2. fruity

1. buttery

12. vinegary

11. musty

10. mothball

9. caramel

8. previous use

7. spicy

2. meaty

3. vegetable

4. sour

5. acrid

6. rubbery

1. rancid

2. sweaty

1. soapy

2. buttery

3. lubricant

4. fat

1. bitter

2. salt

3. sour

4. sweet

1. astringent

2. coating

3. warming

1. pungent

2. drying

1. burnt

2. smoky

3. medicinal

1. cereal

2. malt

3. mash

1. fresh

2. dried

1. orchard

2. tropical

3. citrus

4. berries

5. dried

6. chemical

1. natural

2. artificial

1. grainy

2. cheesy

3. oily

4. sulfury

1. sap

2. cedar

3. oak

4. pine

5. nutty

6. vanilla

fig0001 Figure 1 Whisky flavor wheel. From Lee KYM, Paterson A, Piggott JR and Richardson GD (2001) Origins of flavour in whiskies and a

revised flavour wheel: a review. Journal of the Institute of Brewing 107: 287, with permission.

WHISKY, WHISKEY, AND BOURBON/Composition and Analysis of Whisky 6179

aldehydes exist in equilibrium with the corresponding

acetal and hemiacetal. The most frequently reported

acetal is 1,1-diethoxyethane, though a range of alde-

hydes up to six carbon atoms have been shown to

form acetals.

Sulfur and Nitrogen Compounds

0008 Yeasts have the ability to utilize inorganic sulfur,

sulfur-containing amino acids, and vitamins, and

from these sources, volatile sulfur-containing com-

pounds are produced. The range of compounds

detected includes heterocycles, such as thiazoles and

thiophenes, and aliphatic mono-, di-, and trisulfides.

Formation of sulfur compounds has also been shown

to occur during distillation, and concentrations are

highest in new spirit. Wood extract and traces of

elemental copper are important in the degradation

of such compounds during maturation (Table 2).

Heterocyclic nitrogen compounds such as pyrazines,

pyrroles, and pyridines are formed via the Maillard

reaction during cooking, mashing, distillation, and

barrel charring. As they have relatively low odor

thresholds, they may well make a contribution to

the aroma of whisky. (See Browning: Nonenzymatic.)

Phenols

0009 A wide range of phenolic compounds are found in

whisky. Simple phenols such as phenol, the isomeric

cresols, xylenols, ethyl phenols, and guaiacols arise

through the thermal degradation of benzoic acid

derivatives from malt and from peat smoke. Phenolic

aldehydes such as vanillin, syringaldehyde, conifer-

aldehyde, and sinapaldehyde are formed from the

breakdown of wood lignin during cask charring and

maturation. Their corresponding acids and ethyl

esters have also been detected. Polyphenols extracted

from the wood include ethanol-soluble lignin and

tannins derived from both gallic and ellagic acids.

(See Phenolic Compounds; Tannins and Polyphenols.)

Heterocyclic Oxygen Compounds

0010The main types of these compounds found in whisky

are furaldehydes and lactones. Furfural (2-furalde-

hyde) is formed from pentoses and 5-hydroxy-

methyl-2-furaldehyde from hexoses via the Maillard

reaction during mashing, distillation, and cask char-

ring. Lactones are formed by the dehydration of

aliphatic hydroxy acids, and most are derivatives of

2(3H)-furanones. The most abundant of these are the

cis and trans isomers of 5-butyl-4-methyldihydro-

2(3H)-furanone, the oak or whisky lactones, which

are formed and extracted from oak casks during

maturation.

Variations with Processing

0011Though there are only four basic processes in whisky

production; local, regional, and national variations in

these processes are responsible for the large number of

whiskies available. Each stage of production, from the

production of a fermentable extract, through to fer-

mentation, distillation, and maturation, can affect the

character of the final product. However, each stage is

interlinked, and identifying one, as the most important

for a particular type of whisky, is often impossible.

tbl0001 Table 1 Chromatographic analysis of three samples of a

Scotch malt whisky new distillate

Period (accounting period) 4 4 4

Charge (batch number) 12 14 16

Strength (% v/v) 63.5 71.5 69.4

Acetaldehyde 3.2 3.8 6.8

Ethyl acetate 23.7 25.5 27.0

Diethyl acetal 1.7 1.2 2.2

Methanol 5.1 4.6 5.3

Propanol 40.8 42.7 41.9

Isobutanol 79.8 80.8 80.5

Amyl alcohol

47.7 44.7 49.5

Isoamyl alcohol 142.5 145.5 142.5

Total higher alcohols 331.1 313.7 314.4

Ethyl lactate 4.7 2.5 4.1

Ethyl octanoate 1.6 1.9 1.7

Furfural 3.3 3.9 4.2

Ethyl decanoate 5.7 5.6 4.5

b-Phenethyl acetate 5.7 7.5 5.9

Ethyl laurate 2.1 2.6 2.1

b-Phenylethanol 3.8 0.6 0.6

Ethyl myristate 0.6 1.1 0.6

Ethyl palmitate 2.7 3.3 2.6

Ethyl palmitoleate 1.5 1.9 1.4

Concentrations are grams per 100 liters of alcohol.

Optically active.

From Nicol D (1989) Batch distillation. In: Piggott JR, Sharpe R and Duncan

REB (eds) The Science and Technology of Whiskies, pp. 118–149. Harlow,

UK: Longman Scientific and Technical, with permission.

tbl0002Table 2 Concentrations (micrograms per liter at 100% alcohol)

of sulfur compounds in malt whiskies of various ages

Compounds Age (years)

0 1 2 3^5 6^10

Dimethyl disulfide 359 345 272 149 91

Dimethyl trisulfide 12 16 15 19 14

3-(Methylthio)propanal 7 t 0 0 0

Dihydro-2-methyl-3(2H)-thiophenone 77 53 3 0 0

Ethyl 3-(methylthio)propanoate 21 11 t 0 0

3-(Methylthio)propyl acetate 274 139 3 0 0

2-Thiophenecarboxaldehyde 66 83 49 60 54

3-(Methylthio)propanal 8 0 0 0 0

5-Methyl-2-thiophenecarboxaldehyde 15 15 10 16 16

Benzothiophene 39 27 27 31 38

Benzothiazole 18 16 14 15 32

t, trace.

From Masuda M and Nishimura K (1981) Changes in volatile sulfur

compounds of whisky during aging. Journal of Food Science 47: 104, with

permission.

6180 WHISKY, WHISKEY, AND BOURBON/Composition and Analysis of Whisky

Production of a Fermentable Extract

0012 The cereal grains in common use are wheat, corn

(maize), rye, and barley, though the choice of cereal is

often legally restricted. Flavor differences between

cereals arise from two quite separate sources. The

choice of cereal can also indirectly affect the flavor of

the final product. The composition of the fermentable

extract varies with cereal used and can influence the

metabolism of the yeast. Factors such as pH, amino

acid concentration, and levels of insoluble material are

known to affect the levels of fusel alcohols, acids, and

esters produced, which may influence the flavor of the

final product. Between cereals, differences also exist in

the levels of precursors for a number of classes of flavor

compounds. Examples are compounds formed by the

chemical and enzymatic oxidation of fatty acids, the

reaction of free amino acids and reducing sugars (Mail-

lard reaction), and the thermal degradation of bio-

synthesized precursors like S-methylmethionine and

benzoic acid derivatives. However, the breakdown of

these compounds frequently occurs during fermenta-

tion and distillation and is affected by variations in

these processes. Consequently, no flavors in the final

product have been unequivocally linked to compon-

ents of the original cereal.

Fermentation

0013 Fermentation is responsible for the primary pro-

duction of a large number of flavor compounds in

whiskies. Factors that are known to alter the produc-

tion of these compounds are the strain or mix of

yeasts used, design and level of aeration in the fer-

menter, the duration of the fermentation, and the

presence of contaminating bacteria. These factors

alter according to distillery design and the raw

materials employed and so may be important in pro-

ducing regional and national differences in whiskies.

Distillation

0014 In batch distillation using pot stills, the selection of

the cut points in the still run has a marked influence

on the flavor of the product. Generally, aldehyde and

short-chain ester concentrations are determined by

the primary cut from foreshots to spirit, while the

concentration of fusel alcohols and acids is deter-

mined by the cut from spirit to feints. Other factors,

which affect the physical process of separation during

distillation, are still design parameters such as the

still height, the angle and length of the lyne arm,

and the type of condenser used. In addition, a number

of chemical reactions can occur when the wash or low

wines are heated for distillation. This is particularly

true for batch distillation in pot stills where the heat

impact is greater. Examples include the formation

of sulfur compounds from sulfur-containing amino

acids, the breakdown of unsaturated fatty acids

to carbonyl compounds, and the dehydration of

b-hydroxypropionaldehyde to acrolein. Copper

catalyzes many of these reactions.

0015In continuous stills, congener concentrations are

determined by the design, operation, and efficiency

of the still. The range of reactions described for pot

stills can still occur but becomes progressively less

important as the distillate strength increases. Collec-

tion of spirit at high ethanol concentrations (> 90%)

results in low levels of congeners in the spirit.

Maturation

0016During the maturation period, the new distillate be-

comes highly modified as a result of its contact with

the cask (Figure 2). The composition of the cask

wood has a major effect on the extent of this modifi-

cation and varies with the species of oak used, the

pretreatment applied to the wood, and the previous

use of the cask. In general, American oak (Quercus

alba) yields higher concentrations of vanillin and cis

oak lactone, whereas Spanish oak (Quercus robur)

gives higher concentrations of tannins. Charring in-

creases the levels of lignin breakdown products and

lactones extracted during maturation, whereas previ-

ous use of a cask greatly reduces the amount of

extractable lignin breakdown products and lactones.

The use of sherry casks results in raised levels of

tannins and sugars. The cask is the major determinant

of mature quality, but other factors such as filling

proof, climate, and warehouse conditions also affect

the course of maturation. Higher temperatures pro-

duce greater evaporation rates and also increase

extract levels and some reaction rates, but do not

necessarily produce a more mature product.

Correlation of Chemical Composition with Sensory

Data

0017The flavor of whisky is dependent upon a complex

mixture of components that originate from, and are

modified by, different stages of production. Although

improved analytical methods have revealed much

about the chemistry of whisky, this has not resulted

in a better understanding of the chemical basis of

whisky flavor and quality. Frequently, chemical dif-

ferences can be related to variation in production

processes, but identifying the actual compounds

responsible for the flavor differences has been much

more elusive.

0018The extent to which volatile compounds from

cereals survive fermentation, distillation, and matur-

ation is the hardest to establish. Whisky prepared

WHISKY, WHISKEY, AND BOURBON/Composition and Analysis of Whisky 6181

from heavily peated malt retains a characteristic

flavor that is strongly correlated with the total phenols

content of the malt and of the whisky. However, the

range and concentration of phenols present are

greatly altered by mashing, fermentation, and distil-

lation, and whether the phenols fully explain the

‘peated’ flavor is still uncertain. Likewise, some

whiskies (especially Canadian) have a characteristic

‘spicy’ or ‘minty’ flavor, which is possibly related to

the use of rye in the mash, but no compound has been

identified as responsible.

0019 Various flavors in new distillates have been correl-

ated with sulfur compounds. Polysulfides are present

in whisky at levels around and above their sensory

thresholds (3–6ngg

1

for dimethyl trisulfide), and

the data available suggest that these compounds are

correlated with ‘sulfury’ and ‘heavy’ characters in

fresh distillates. Other sulfur-containing compounds

are thought to be important contributors to flavor,

and their formation is dependent on the levels of

precursors present in different cereals/cultivars. How-

ever, such compounds are frequently formed during

fermentation and distillation and then degraded

during maturation. Each stage has its own impact

on the concentration in the final product, making it

harder to establish their role in whisky flavor.

0020 The products of fermentation and distillation make

a substantial contribution to whisky flavor. However,

these compounds, except when present in excess,

appear to form what has been described as the

‘integrated whisky complex,’ and their individual

contributions have not been determined. It does

appear that relatively constant proportions of some

of these compounds must be present for a recogniz-

able ‘whisky’ character, though substantial changes

can occur with only minor changes in flavor.

0021Compounds considered to be important in matur-

ation are vanillin, eugenol, and cis oak lactone. These

have been correlated to ‘vanilla’ and ‘clove-like’

flavors in some whiskies matured in new casks. How-

ever, cask reuse causes a general decrease in wood

extractives, and their importance in whisky matured

in refill casks is still uncertain.

0022Attempts to create a model of whisky flavor have

been largely unsuccessful. Attempts were based on

compositional analyses of the liquid. Research has

since shown that there are complex relationships

governing the release of flavor compounds from

whiskies. Major factors identified include alcoholic

strength and the nonvolatile content of the whisky

matrix. Dilution of spirits for sensory assessment,

to reduce the pungency of ethanol, can greatly alter

the release of aroma compounds more soluble in

ethanol than in water. Dilution also increases the

capacity for matrix effects that suppress the release

of ethyl esters and other aroma compounds. Matrix

effects may occur through competition for release at

the liquid surface or changes in solubility of flavor

components. Changes in solubility can be related

to the physical structuring of the ethanol–water

120

160

200

240

280

320

360

2 3 4 5 6 7 8 9 10 11 12

Congener concentration (g per 100 proof liters)

Age (years)

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Color (absorbance at 430 nm per 100⬚ Proof)

Color

Total solids

Total acids Tannins Esters Aldehydes

fig0002 Figure 2 Congener changes during maturation of whisky. From Reazin GH (1981) Chemical mechanisms of whisky maturation.

American Journal of Enology and Viticulture 32: 283, with permission.

6182 WHISKY, WHISKEY, AND BOURBON/Composition and Analysis of Whisky

mixture. Differential scanning calorimetry, light scat-

tering, and mass spectrometry have all demonstrated

that physical changes occur during maturation,

adding another layer of complexity to whisky flavor

and reinforcing the uniqueness of each individual

product.

See also: Browning: Nonenzymatic; Chromatography:

High-performance Liquid Chromatography; Gas

Chromatography; Flavor (Flavour) Compounds:

Structures and Characteristics; Mass Spectrometry:

Principles and Instrumentation; Phenolic Compounds;

Sensory Evaluation: Taste; Tannins and Polyphenols

Further Reading

Campbell I (ed.) (1990) Proceedings of the Third Aviemore

Conference on Malting, Brewing and Distilling.

London: Institute of Brewing.

Campbell I (ed.) (1999) Proceedings of the Fifth Aviemore

Conference on Malting, Brewing and Distilling.

London: Institute of Brewing.

Campbell I and Priest FG (eds) (1986) Proceedings of the

Second Aviemore Conference on Malting, Brewing and

Distilling. London: Institute of Brewing.

Campbell I and Priest FG (eds) (1995) Proceedings of the

Fourth Aviemore Conference on Malting, Brewing and

Distilling. London: Institute of Brewing.

Nyka

nen L and Lehtonen P (eds) (1984) Flavour Research

of Alcoholic Beverages. Helsinki: Foundation for Bio-

technical and Industrial Fermentation Research.

Nyka

nen L and Suomalainen H (1983) Aroma of Beer,

Wine and Distilled Alcoholic Beverages. Dordrecht:

Reidel.

Piggott JR (ed.) (1983) Flavour of Distilled Beverages:

Origin and Development. Chichester, UK: Ellis Hor-

wood.

Piggott JR and Paterson A (eds) (1989) Distilled Beverages

Flavour: Recent Developments. Chichester, UK: Ellis

Horwood.

Piggott JR, Sharp R and Duncan REB (eds) (1989)

The Science and Technology of Whiskies. Harlow, UK:

Longman.

Priest FG and Campbell I (eds) (1983) Current Develop-

ments in Malting, Brewing and Distilling. London:

Institute of Brewing.

WILD RICE

O W Archibold, University of Saskatchewan,

Saskatoon, Canada

Background

0001 Wild rice is an aquatic grass that grows naturally in

shallow lakes and slow-moving rivers (Figure 1) in the

Great Lakes region of North America. It is North

America’s only native cereal, and until very recently

had not been improved by breeding and selection.

Lake-grown wild rice is unique amongst commercial

crops in that it is grown and harvested on water and,

once established, will reseed itself indefinitely. Wild

rice was an important staple of the indigenous

peoples of the Great Lakes region and remains part

of many legends and ceremonies. The range of the

species was initially extended by the early European

voyagers who took wild rice with them to establish

food supplies along the waterways that they traveled.

Recent commercial exploitation has greatly increased

production and extended the crop well beyond its

native range. Most of the wild rice is now produced

in artificial paddies and combines have replaced

the traditional hand-harvesting methods. Vigorous

marketing and product development have created

global markets for this highly nutritious crop.

Taxonomy and Tradition

0002The contemporary common name ‘wild rice’ applies

to annual species of Zizania, emergent aquatic grasses,

which are native to eastern and central North Amer-

ica. Four forms are generally recognized on the basis

fig0001Figure 1 Shallow bays supplied with nutrients from slow-

moving streams provide the ideal wild rice habitat.

WILD RICE 6183

of morphology, range, and habitat. The exclusively

riparian species Z. aquatica L. includes the variety

aquatica (Hitch.) Fassett (southern wild rice) and the

variety brevis (Fassett) Dore (estuarine wild rice). A

second species, Z. palustris L. is comprised of the

variety palustris Dore (northern wild rice) and the

variety interior (Fassett) Dore (interior wild rice).

Zizania palustris is the most widespread species; it is

also the species of commercial value, owing to its

large seed size. Northern and interior wild rice are

found in the upper Mississippi–Great Lakes region,

extending into the boreal forest. These two varieties

are sympatric over much of their ranges, although a

latitudinal gradation in dominance is acknowledged.

0003 Wild rice grows naturally in shallow lakes and

streams, and is a traditional crop of the native peoples

of the upper midwestern USA and central Canada.

The grain was a staple diet for these seminomadic

peoples, and was a cherished resource that was vigor-

ously guarded for food and trade. French explorers

noted the resemblance of wild rice to tares, a trouble-

some weed of wheat, and during this period it was

known as ‘folle avoine.’ Indeed, the scientific name

chosen by Linnaeus comes from the Greek zizanion –

a weed of Mediterranean grainfields. By the early

nineteenth century, English-speaking explorers called

the grain ‘wild rice’ or ‘Indian rice’ because its aquatic

habitat reminded them of Asiatic white rice (Oryza

spp.). Wild rice, and the French Canadian equivalent

‘riz sauvage,’ remain the common names for the

species. By the end of the nineteenth century, non-

Native Americans started to become interested in the

potential of wild rice as a commodity, first as brokers

assuming control of wild rice processing and sale,

then as planters and farmers, ultimately gaining con-

trol of the industry. Records of treaty negotiations

show repeatedly the attempts by native Americans

to explain the importance of their natural resources.

Various federal and state laws have been passed which

recognize the traditional value of the crop, and specify

the type of equipment that can be used and the amount

of wild rice that can be collected. Consequently, most

of the lake-grown wild rice in Minnesota and Wiscon-

sin is under control of Native Americans. Legislation

in Canada similarly provides for aboriginal involve-

ment in wild rice production in the pristine northern

lakes. However, increased commercial demand and

high commodity prices in the late 1970s resulted in

the rapid establishment of artificial paddies which

now account for most of the production.

Life Cycle of Wild Rice

0004 Wild rice is an annual plant that grows each year

from seed and requires approximately 120 days to

mature. Under natural conditions ripe seeds shatter

into the lakes. The seeds do not germinate until they

have been subjected to an afterripening period of

several months at low temperatures. Dormancy is

broken naturally during the long boreal winters

while the seeds lie embedded in the mud beneath the

frozen lake. Freezing does not harm the seeds and

germination begins in late spring, when water tem-

peratures rise to about 5



C. For the first 3 or 4 weeks

of growth the young plants are under water, then

long, thin leaves reach the surface as the plant enters

the floating-leaf stage. By the end of June the stem

and leaves begin to emerge from the water and the

plant enters the aerial-leaf stage. Additional stems

(tillers) may arise from the lower part of the stem

and increase the density of the stands.

0005Flowering commences in mid-July, with separate

male and female florets forming a branching panicle

up to 50 cm in length, although considerable vari-

ation in panicle size occurs within and between nat-

ural stands. The flowers mature from the top down.

The female (grain-producing) flowers nearest the top

are the first to bloom, and it can take several weeks

for all of the flowers to mature. Wild rice is wind-

pollinated. The female flowers remain receptive to

pollen for only a few days and so receive pollen from

the male flowers on other plants; this insures cross-

pollination and high genetic diversity. The grains take

4–6 weeks to mature following pollination. During

this time the maturing grain passes through the soft-

textured milk and dough stages until it becomes firm

and greenish-black in color within the encasing hull.

The first seeds usually ripen by the end of August, and

must be harvested quickly because they shatter read-

ily. However, seeds will continue to ripen over a

period of several weeks until the plant is killed by

frost. Seed loss, even in harvested stands, is normally

sufficient to maintain stands from year to year.

Environmental Conditions in Natural

Stands

0006Wild rice growing in unmanaged habitats is sensitive

to the vagaries of the weather. In the early stages of

growth, water depth and wind are critical because the

young plants can be drowned or uprooted by wave

action. The ideal water depth is 75–100 cm. Mature

grains can be lost under windy conditions, and in

some areas the harvest period is often cut short be-

cause of frosts. Wild rice production is also influenced

by numerous site-specific environmental factors.

Wild rice does not grow well in acidic water that is

low in essential nutrients; neither will it grow well in

alkaline and saline water. Total alkalinity ranging

from 40 to 80 mg l

1

and pH values ranging from

6184 WILD RICE

6.9 to 7.4 are considered optimal, although the rela-

tionship between sediment chemistry and wild rice

production is tenuous. Wild rice will grow on a var-

iety of sediments, but the most productive stands are

typically associated with soft organic materials that

are easily permeated by the coarse fibrous roots. The

state of oxidation of the sediment is an important

factor affecting production, and many lakes seeded

to wild rice seem incapable of nurturing the crop

when E

(redox) values are below 200 mV.

0007 Wild rice growing in lakes does not compete well

with taller, emergent perennials such as spike-rush

(Eleocharis palustris) and cattails (Typha latifolia),

which renew growth early in the spring. Similarly,

floating-leaved aquatics such as water lilies (Nym-

phaea spp. and Nuphar spp.) and bur reed (Sparga-

nium spp.) can also be problematic. In paddies

common water-plantain (Alisma trivale) and various

aquatic grassy weeds are of concern as no herbicides

have been cleared for their control. Intraspecific com-

petition for light and nutrients can also occur in very

dense stands of wild rice and some paddies are

thinned to increase in production.

0008 Lake-grown wild rice is relished as a food source by

waterfowl, muskrats, beavers, and moose, while red

wing blackbirds (Agelaius phoeniceus) and crayfish

(Orconectes virilis) are pests in the paddies. Insect

depradation and losses from fungal, bacterial, and

viral diseases have also been reported. Most damage

is attributed to the riceworm (Apamea apamiformis)

which feeds on the developing grain and the rice stalk

borer (Chilo plejadelus) which feeds on the lower

stems, making them susceptible to breakage or caus-

ing incomplete development of the grain. Reduced

yields are also attributed to leaf spot, smut, and

similar microbial pathogens. Ergot has long been

associated with wild rice.

Agronomic Development

0009 The natural range of wild rice has been extended

through deliberate introduction, but early expansion

of the industry was hampered by unreliable yields

from stands in natural lake environments. The first

attempts to domesticate the crop began in the 1950s

when wild rice was grown in Minnesota in dyked

paddies where a water depth of about 30 cm could

be maintained during the growing season. A further

significant development occurred in 1968 when the

nonshattering Johnson cultivar was introduced. In

Minnesota this has largely been replaced by earlier-

maturing cultivars such as K2, Voyager, and Franklin.

Shattering resistance requires the crop to be harvested

by specially modified combines and grain losses have

been significantly reduced. The paddies are drained

prior to harvest and must be reseeded to wild rice in

much the same way as other grain crops.

0010Agrochemicals are also used to maximize paddy

production. Ammonium phosphate or urea is com-

monly incorporated into the upper few centimeters of

the soil during seedbed preparation together with

phosphate and potash; nitrogen topdress applications

may be desirable as the stem begins to elongate.

Fungicides may also be needed. Weeds are usually

controlled by water management, while pests, such

as blackbirds and crayfish, may also need to be con-

trolled. Such agronomic developments have reduced

the problem of unpredictable yields, thereby facilitat-

ing expansion of commercial markets for wild rice.

0011By 1978 more than 4000 ha of paddies had been

established in Minnesota, and production approached

1.0 million kg of processed wild rice compared to

0.46 million kg from lakes. This year is significant

because in 1978 paddy wild rice cultivation com-

menced in California. By 1986 production in Califor-

nia exceeded 4 million kg (processed) compared to

2.3 million kg in Minnesota. Paddy acreage in Min-

nesota is now about 6500 ha compared to about

3200 ha in California, with combined production cur-

rently about 5.0 million kg; this accounts for more

than 90% of the world’s supply. Approximately 0.4

million kg is produced annually in Canada, mainly

in Saskatchewan, Manitoba, and Ontario. The re-

mainder comes mostly from Idaho, Wisconsin, and

Oregon. Although trials have been conducted in Fin-

land, at present wild rice is not grown commercially

outside North America.

Harvest

0012In traditional harvests wild rice is collected by

knocking the grain into canoes using two sticks. It is

then dried in partial shade to avoid mildew, picked

over to remove pieces of stem and leaves, then

parched by smoke drying or scorching in kettles.

Each kernel is enclosed by a hull comprised of a

scabrous lemma and palea which is difficult to

remove until it has been heated. Once detached

from the seed by treading or threshing, the chaff is

removed by tossing in the air with large winnowing

trays. The kernels left in the tray are then ready for

cooking or storage. The traditional stages of process-

ing have been adopted by the commercial plants that

handle the massive increase in yield harvested mech-

anically from the paddies. Dyked and ditched fields

allow water levels to be closely regulated at all stages

of production, and fertilizers and pesticides are

applied as necessary to optimize yields. In August

the paddies are drained to allow access by modified

combine harvesters. After a period of drying to help

WILD RICE 6185

eliminate weeds, the soils are prepared for seeding the

next year’s crop. Paddies in Minnesota are planted in

the fall and reflooded the following spring. In Cali-

fornia the seed must be kept in cold storage to break

dormancy prior to planting in the spring.

0013 Lake-grown wild rice differs from other crops be-

cause it is grown and harvested on water. Unlike the

nonshattering paddy cultivars, lake-grown plants

must be harvested regularly to minimize grain losses.

Wild rice kernels mature gradually, beginning in

August and continuing for 15–30 days, depending

on weather conditions. About 3–6% of the potential

yield matures each day. Maximum production can

therefore be achieved if harvesting is repeated regu-

larly during the ripening stage. A wild rice plant can

develop many stems, particularly in shallow-water

sites. These tillers are capable of producing the

same-quality grain as the main stem. However, tillers

generally come into flower later than the main stems.

Maximum yields can only be achieved if the area is

harvested several times. Normally, harvesting is

repeated every 4–7 days. Most of the lake-grown

wild rice now comes from Canada and is harvested

by propeller-driven airboats. The most widely used

design consists of a blunt-bowed, flat-bottomed alu-

minum hull about 3.6 m long and 1.5 m wide fitted

with a collecting tray, popularly known as a speed-

head (Figure 2). The sides and rear of the speedhead

frame are covered with window-screening material.

The speedhead has no moving parts; the kernels are

dislodged through the impact of the wild rice plants

against the leading edge and they fall into the tray.

Processing and Grading

0014 Freshly harvested wild rice for processing must be

delivered to the plant as soon as possible. The grade

and appearance of the finished product depend a

great deal on how the wild rice is handled. Careful

storage is important in that it helps begin the curing

process. Not all of the wild rice is at the same stage of

maturity, and it is necessary to pile it in windrows to

allow it to cure. The windrows are watered regularly

to prevent self-heating and drying. They must also

be turned daily to prevent decay. It is during this

4–10-day period that the wild rice acquires its famil-

iar black color and flavor, and the hulls also begin to

loosen. When the grain is properly cured it passes into

the parching ovens. Parching removes moisture from

the kernels and toughens them so they will not break

as easily. Smaller batch parchers will hold up to

275 kg of wild rice, and the drum is rotated to prevent

the grain from burning. Larger processing plants use

continuous-flow parching. It takes about 2 h for the

grain to pass through the parcher at temperatures of

145



C in these automated systems. Wild rice can be

loaded into continuous-flow parchers at a rate of up

to 400 kg h

1

0015The primary purpose of parching is to reduce the

moisture content of the kernel to about 7% without

fracturing. In addition, the hull is loosened, pigmen-

tation of the pericarp is completed, and the flavor of

the grain is brought out. Steam retention in closed

parchers helps to give a glassy, translucent appear-

ance to the grain by gelatinization of the starchy

endosperm. After parching, leaf and stem fragments

are removed by screening, and ferrous metals are

trapped by magnets on the conveyors. The hot kernels

immediately pass into the hulling machines where the

dry hulls are removed. The kernels are dehulled by

passing through a roll huller which consists of two

closely spaced, rubber-faced rollers which rotate to-

wards each other at different speeds. This strips the

hulls off and makes the kernels look black and shiny.

Some processing plants use a barrel huller in which

rubber cogs rotate at high speed. The hulls and the

kernels fall into an aspirator that sucks off the lighter

chaff. Once the hulls are removed, the wild rice is

cleaned by passing over vibrating screens to separate

unhulled grain, stones, and other heavy materials.

Once broken kernels have been sorted, the intact

kernels are graded by size on a gravity table prior to

inspection and packaging. Most plants use 45-kg

sacks to bag the final product for storage.

0016Various grades of wild rice have been proposed by

the Processors Committee of the International Wild

Rice Association, mainly on the basis of size. The

longest kernels command the highest market prices,

as they are preferred by the gourmet culinary trade.

For long-grain wild rice (grades 1 and 2), kernel

length is greater than 1.03 cm, medium-grain wild

rice (grade 3) is 0.79 cm, short-grain wild rice (grades

fig0002 Figure 2 Propeller-driven airboat used to harvest lake-grown

wild rice.

6186 WILD RICE

4 and 5) is 0.40 cm, with smaller kernels classed as

small and broken wild rice (grades 6 and 7). These

grades are further defined according to the percent-

ages of kernels of each size. Long-grain wild rice

requires a minimum of 85% long grains, and a max-

imum of 10% medium, 7% short, and 3% broken

grains. Medium-grain wild rice contains a minimum

of 80% medium grains and a maximum of 10% long

grains, 10% short grains, and 7% broken; short-grain

wild rice contains a minimum of 80% short grains,

a maximum of 10% broken, 5% long, and 10%

medium kernels. The average kernel weighs approxi-

mately 50 mg.

0017 Four quality grades of wild rice are recognized –

premium, choice, good, and standard – on the basis of

foreign materials such as dust and chaff, unhulled

grain, or weed seeds, damaged kernels, and percent

moisture. Color, taste, and odor also affect product

quality. Blackish-brown kernels are favored and qual-

ity is reduced if the thin bran peels off and exposes the

white endosperm. The kernels also lose some of their

color when some of the bran is removed through

scarification. However, this is necessary to hasten

cooking time and allows wild rice to be used in

blended-rice products. Improperly processed rice

which contains green kernels that have not been

fully fermented or which lacks the preferred toasted

flavor or has a musty odor is not acceptable. Moisture

content is reduced to less than 7% during processing.

This facilitates long-term storage, but stress cracks

which develop due to excessive heat during parching

make it susceptible to damage during subsequent

handling.

0018 Wild rice is considered a specialty by retailers and

is often sold in regional airports and tourist resorts in

attractive transparent packages or ornamental con-

tainers. Appearance is an important aspect of quality

and customer appeal and broken kernels render the

product less desirable. Lake-grown wild rice is nor-

mally larger than paddy-grown cultivars and so com-

mands higher prices, but they are indistinguishable in

terms of nutritional value.

Composition and Food Quality

0019 In the traditional native diet, wild rice was more

nutritious than other naturally available fruit, grain,

or animal food sources. The wild rice kernel is similar

in structure to other cereals. It consists of an embryo,

a starchy endosperm, and an aleurone layer encased

in a tough, impermeable pericarp. Wild rice has good

nutritional value; it is rich in carbohydrates and high

in protein and minerals, but low in fats and oils

compared to other cereals. Starch accounts for ap-

proximately 75% of the dry weight of the kernels,

protein averages about 13%, dietary fiber 7%, sugars

2%, minerals 2%, and oils and fats 1% (Table 1).

Many amino acids are present at concentrations that

are adequate to meet daily human requirements.

Lysine, threonine, and methionine, important indica-

tors of nutritional quality of cereals, are typically

present at higher concentration in wild rice than in

other grains (Table 2). Very little amino acid is lost in

processing, whereas essential minerals (Table 3) are

mainly present in the pericarp, and a considerable

reduction occurs when wild rice is scarified or pol-

ished. Vitamin A is absent from processed wild rice,

but it is a good source of dietary B-vitamins, espe-

cially niacin and thiamin (Table 4). Linoleic and lino-

lenic acids are comparatively abundant and together

make up about 70% of the total fatty acid content in

wild rice. Although this is desirable from a nutritional

standpoint, it can lead to problems of rancid odor if

oxidation occurs because of improper storage. How-

ever, properly cured and stored wild rice remains

wholesome for several years.

0020Wild rice has also attracted the interest of the

food-processing industry because it contains the

antioxidant phytate (myoinositol hexaphosphate).

Additions of 15% by weight of cooked wild rice to

beef patties has been shown to reduce rancidity by

reducing the production of thiobarbituric reactive

substances by as much as 50%. This has a significant

potential in microwavable precooked meat products,

especially as studies have shown consumer taste pref-

erences for meat patties blended with wild rice. In

addition, nutritive properties are enhanced, choles-

terol and fat percentages are reduced, and cooking

yields are augmented. Similar antioxidant properties

were found with extracts from wild rice hulls; these

are presently discarded at the processing plants. Wild

rice starch has been shown to have a low degree of

retrogradation and this may be useful in the paper,

textile, and adhesive industries where changes in

prepared batches of pastes are undesirable.

tbl0001Table 1 Typical composition of wild rice and other cereals

(g 100 g

1

of dry product)

Wild rice Brownrice Yellow

corn

Hard

wheat

Oat

groat

Starch 74.0 78.0 71.5 66.5 62.0

Protein (N 5.7) 13.5 8.7 9.0 14.5 15.5

Dietary fiber 6.8 5.3 9.5 11.5 11.0

Sugars 1.7 1.3 2.3 1.7 1.4

Oils and fats 0.8 2.6 4.7 1.8 6.5

Ash 1.8 1.5 1.5 2.0 2.0

After Anderson RA (1976) Wild rice: nutritional review. Cereal Chemistry

53: 949–955, with permission.

WILD RICE 6187

0021 Contamination of the wild rice habitat has

prompted concern about elevated levels of toxic

metals in the kernels which might pose a health

hazard. Copper concentrations as high as 14.4 mg

1

and lead and cadmium levels as high as 6.2 and

6.7 mgg

1

respectively have been reported in some

samples of parched and dehulled wild rice. Locally

elevated metal concentrations have been attributed

to atmospheric deposition from smelters, and it

has also been reported that lead derived from

shotgun shells can be taken up by wild rice. Concen-

trations of lead (0.5–11.5 g 100 g

1

dry weight), cad-

mium (1.0–10.2 g 100 g

1

dry weight), and arsenic

(0.6–14.2 g 100 g

1

dry weight) have been found in

wild rice sold in the USA.

Concluding Remarks

0022Interest in wild rice from companies like Uncle Ben’s

and General Foods has spurred the development of

the industry. Blended products containing 12–18%

wild rice mixed with long-grain white or brown rice

have increased on the supermarket shelves. The

smaller grain sizes developed by breeders have elim-

inated the problems of lengthy cooking times and,

coincidentally, increased the number of grains per

package, thereby making it more attractive to con-

sumers. With increasing acceptance of wild rice, a

variety of products began to emerge, including stuff-

ings, frozen casseroles, bread and pancake mixes, and

puffed rice snacks, as well as a myriad of cookbooks

and recipes. However, natural lake-grown wild rice

continues to be the preferred choice of the gourmet

and health-food markets. In an effort to maintain

some control of the market, native growers were

successful in getting legislation requiring that paddy-

grown rice be so labeled, thus distinguishing it from

the traditional product. Attempts by Native Ameri-

can organizations to compete or cooperate with the

larger companies have not been overly successful. In

effect, the white-monopolized industry has caused a

reversion of wild rice to its traditional role as a sub-

sistence item in the Native American economy.