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

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subsurface floating structure. Alternatively, oysters

may be held just off the bottom on a series of trays

and frames. The most common systems employ a

longline, a rope, up to 250 m or longer, supported

by floats and anchored to the seabed at several points

to ensure stability. From this main rope are hung

vertical droppers that hold animals directly, e.g., bys-

sally attached mussels, or, for ear-hung scallops, the

shell is pierced and attached via nylon line.

0012 More commonly, a cage or net holds animals. Lan-

tern nets are a collapsible net stocking with multiple

horizontal platforms holding shells, individual pearl

nets have a rigid frame, and vertical panel nets con-

tain numerous pockets in which individuals are

placed. For lower-intensity operations, or for some

particular species, such as the South-East Asian Rudi-

tapes and Meretrix clam species, and the American

hard clam (Mercenaria mercenaria), growout is based

on seeding of suitable sandy/mud nearshore areas.

The juveniles may be produced in the hatchery or

collected in the wild.

Production Methods (Gastropods)

0013 The main gastropods under cultivation are abalone,

and, although production systems are still under

development, their high value and declining wild

harvest give them significant potential. Production

now comes from China, Chile, South Africa, Austra-

lia, New Zealand, and the USA. The principal culture

methods include a suspended lantern net system,

using larger and more structurally complex cages

than for bivalves, and raceway culture in long,

narrow glass fiber or concrete tanks, within which

flat plates are inclined to provide shelter and a surface

for growth of algal feed. Tidal pond culture is also

practiced in China, though less frequently than other

methods.

0014 Abalone culture relies on hatchery-produced

juveniles, and broodstock are spawned using similar

methods to bivalves. The larval development of

abalone is similar, though shorter at 7 days or less,

and nonfeeding, so provision of algae is not necessary.

At settlement, the larvae metamorphose into the

bottom-living form. This transitional phase from

larvae to settled juveniles remains the period of

highest mortality. At settlement, larvae are induced

to attach to corrugated plastic or tiles, which have a

surface growth of algal and bacterial cells. The juven-

iles feed on these films and, as growth continues,

are transferred to nursery and growout systems.

The options of open-water ranching or restocking

depleted areas have also been attempted and have

the advantage of no management input, but the dis-

advantage of little control over stock.

Current Issues and Future Prospects

0015As with most aquaculture, there is a tendency away

from wild seed collection, for sustainability and

supply reasons, but also for benefits from hatchery

production. These include genetic selection (e.g.,

faster growth rates, disease resistance) and genetic

manipulation to develop polyploid animals, i.e.,

three or four copies of genes, compared with two.

Polyploid animals may be reproductively inactive,

essential for translocation of non-native species to

open-water systems, and often show increased

somatic growth rates owing to reduced gonadal de-

velopment. Continued vigilance in the control and

detection of toxic algal blooms and monitoring

for product safety will remain significant issues if

public confidence in mollusc consumption is to be

maintained.

Crustaceans

0016Most aquacultured crustaceans belong to the Class

Malocostraca, Order decapoda, e.g. prawns/shrimps,

crabs, lobsters, although brine and mysid shrimp

(Classes Branchiopoda and Mysidacea) and copepods

(Class Copepoda) are also produced in small quan-

tities as live feeds for other aquaculture species,

such as finfish. Decapod production is dominated by

the marine penaeid prawns, with the black tiger

prawn (Penaeus monodon) being the most widely

cultivated crustacean worldwide. In 1999, produc-

tion was 575 842 tonnes, predominantly from Asia,

with an estimated value of US$3.65 billion. P. vanne-

mei and P. chinensis are the aquacultured penaeids in

the Americas and China, respectively, contributing

359 196 tonnes. Penaeids are grown worldwide

(Table 2).

0017The giant river prawn (Macrobrachium rosenber-

gii), is the most widely cultured freshwater decapod

crustacean, with production in 1999 of 102 124

tonnes, worth US$416 million. It has been introduced

into many countries, including North and South

America, Africa, Asia, and the Pacific Islands.

China, Bangladesh, and Taiwan account for over

90% of production. Freshwater crayfish culture is

widespread and based on six main species (in order

of quantity): Procambarus clarkii, Pacifastacus

leniusculus, Astacus leptodactylus, Cherax destruc-

tor,andC. quadricarinatus. Total production

amounted to 21 171 tonnes in 1999, with US produc-

tion of P. clarkii over 19 000 tonnes alone. Other

minor species are produced locally (Table 3).

0018Crab aquaculture production is relatively small

and dominated by the freshwater Chinese river crab

(Eriocheir sinensis) at 171 955 tonnes in 1999.

SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans 5247

Additional species under small-scale culture, but with

potential, include the mud crab (Scylla serrata)and

various portunid swimming crabs.

0019 Lobster culture worldwide is extremely small, 58

tonnes from four different Panulirus spp., a tropical/

subtropical genus. The slow development of lobster

culture is due to a relatively long larval cycle that is

technically difficult to replicate in hatcheries.

Crustacean Nutrition

0020 The larval stages of crustaceans vary in their nutri-

tional requirements. Typically, under hatchery condi-

tions, early stages feed on stored yolk, before moving

to phytoplankton then zooplankton, e.g., Artemia

(brine shrimp) larvae or rotifers. Crabs and lobsters

may be carnivorous from hatching.

0021 Penaeid prawns are fed a processed pelleted diet,

consisting principally of marine fish meal, and

additionally balanced for nutritional requirements.

The food conversion ratio, i.e., the quantity of feed

(kg) required to produce 1 kg of product is typically

around 1.5–2.5:1, in semi-intensive/intensive penaeid

production systems.

0022Feed is a major cost and may constitute around

30% of production costs. Uneaten feed is a major

contributor to poor water quality, and nutrient-rich

waste water contributes to external environmental

impacts. Feed management is vital for successful

aquaculture.

0023Freshwater crayfish are omnivores and obtain

much of their nutritional requirements from the

culture environment in the form of organic detritus.

Grain-based pellets, or hay, are often added to ponds

to provide additional feed and promote pond prod-

uctivity by enhancing nutrient levels.

0024Crabs, such as Scylla spp., are also omnivores but

with a tendency towards animal protein. Crab aqua-

culture is still relatively undeveloped, to the extent

that no standard feed is produced or used. Most

production is from South-east Asia, and much use is

made of local feed sources such as trash fish and

shrimp, squid, and plant meals such as soy. Pen

culture in mangrove areas also provides additional

nutrition in the form of fallen mangrove leaves.

0025A feeding behavioral characteristic of many crust-

aceans, and one that heavily influences production

management, is cannibalism. Crustaceans are most

vulnerable immediately after molting, a regular pro-

cess essential for growth. When the old, hard exo-

skeleton is shed, the animal is soft until the new shell

hardens and is vulnerable to predation, especially if

stocking densities are high. Cannibalism is less

common in penaeids and crayfish, where it is man-

aged by appropriate stocking, size grading and feed-

ing regimes, but more common in crabs and lobsters.

Similar management strategies are again employed

but are not wholly effective. As a consequence, crab

production densities tend to be low, and separation

into individual culture vessels has been employed for

cultivated soft-shell crab and Hommarid lobsters.

The associated cost of this makes it viable only

for high-value products, or short-term culture of

juveniles for restocking purposes.

Production Methods

0026Decapod crustaceans are characterized by complex

and diverse larval cycles, which, as previously noted,

have contributed to their relative ease and develop-

ment of aquaculture. Differences in larval cycles also

contribute to differences in production methodologies.

0027Hatchery The most commonly cultured crustaceans,

the penaeid prawns, are unusual in having no maternal

tbl0002 Table 2 Principal aquacultured penaeids and main production

sources

Species Sources

Penaeus monodon

Giant tiger prawn

Thailand, India, Vietnam,

Indonesia, Philippines

Penaeus vannamei

Whiteleg shrimp

Ecuador, Mexico, Brazil, Colombia

Penaeus merguiensis

Banana prawn

Vietnam, Indonesia

Penaeus stylirostris

Blue shrimp

Ecuador

Penaeus chinensis

Fleshy prawn

China, Korea

Penaeus japonicus

Kuruma prawn

Japan, China, Australia

Penaeus indicus

Indian white prawn

India, South Africa

tbl0003 Table 3 Principal aquacultured freshwater crayfish and main

production sources

Species Source

Procambarus clarkii

Red swamp crawfish

USA, Mexico, France (I)

Pacifastacus leniusculus

Signal crayfish

France (I), Spain (I)

Astacus leptodactylus

Danube crayfish

France

Astacus astacus

Noble crayfish

France

Cherax destructor

Yabby

Australia

Cherax quadricarinatus

Redclaw crayfish

Australia, Argentina (I), Mexico (I)

Cherax tenuimanus

Marron

Australia, South Africa (I)

I, introduced.

5248 SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans

care, and fertilized eggs are shed directly into the

water. Most decapods retain the developing larvae,

within the egg, on modified appendages beneath the

abdomen, e.g., freshwater crayfish and crabs, and

release larvae at a later developmental stage.

0028 For aquaculture operations, mature broodstock are

typically sourced from wild populations, although

farm-reared broodstock are becoming more common

as they enable reliable supply and the opportunity for

genetic selection. Broodstock are maintained in spe-

cialized spawning tanks, under conditions of reduced

density and high-quality nutrition favoring gonad

development. Environmental variables such as tem-

perature and light intensity are also controlled to

reduce stress and promote gonad maturation. Mating

involves transfer of a sperm package that the female

retains until required, and fertilization typically

occurs as the eggs are released. Spawning occurs

under relatively predictable circumstances following

ovary maturation, enabling hatcheries to harvest eggs

as they are produced.

0029 Penaeid eggs hatch within about 12 h into the

nauplius phase, which persists through several stages,

before progressing through major metamorphoses

into protozoeal, mysis, and postlarval phases. The

duration of the whole larval cycle, up to saleable

postlarva (PL) is typically around 20–25 days. The

larval phase, whether in open water or in the hatch-

ery, is a free swimming period, becoming the more

familiar bottom-living form after the postlarvae

phase.

0030 Growout Typically, the postlarval stage is trans-

ferred from the hatchery to grow out ponds, although

some operations also have intermediate nursery

growout or conduct growout in indoor, tank-based

systems under high-density conditions. However,

growout is generally earthen pond-based, ranging in

size from less than 0.5 ha to over 10 ha, although

larger ponds are typically harder to manage effect-

ively. Ponds are generally 1–2 m in depth and are

stocked with PL at between 1 (or less) to more than

100 PL m

2

, depending on the production type. For

example, Australian stocking rates for P. monodon

under relatively intensive 1-ha pond production is

30–40 PL m

2

0031 During the production cycle of 3–4 months, water

quality is managed through aeration, water exchange,

and a phytoplankton bloom, which tends to stabilize

physicochemical water parameters, e.g., oxygen,

carbon dioxide, pH. Feed is provided three or four

times per day, with consumption closely monitored

and adjusted as necessary. Production from such inten-

sive penaeid culture is typically 5–10 tonnes per hec-

tare per crop but varies with species and management.

For other crustaceans, the principal differences in

larval development and production methods are

as follows.

0032Freshwater Crayfish Females hold 500–800 eggs

under the abdomen that hatch as miniature crayfish

after 2–10 weeks, depending on the temperature and

species. Juveniles are collected and graded for size

and gender, and stocked at around 5–15 m

2

(e.g.C. quadricarinatus), typically into earthen

ponds. Production of this species seldom exceeds 1–

1.5 tonnes per hectare per crop, owing to lower dens-

ities and lower intensity management.

0033Crabs The crab larval phase begins as a zoea, of

which there are five, followed by megalopa then

crab. Although still developmental, pond-based cul-

ture for Scylla spp. crabs appears feasible. Small-scale

commercial trials have indicated that monosex cul-

tures, low–medium stocking densities, and provision

of shelters, to protect newly moulted individuals from

cannibalism, provide improvements on current low-

intensity culture systems. Polyculture with penaeids,

as a secondary crop, also occurs.

0034Perhaps the greatest opportunity for value adding

to crab culture is a soft-shell product. Soft-shell crabs

have been a valuable secondary product of the eastern

US blue crab (Callinectes sapidus) fishery for more

than 100 years. The development of culture tech-

niques, and the ability to control aspects of molting,

should enable commercial scale production within a

few years. Presently, it remains labor-intensive and

confined largely to South-east Asia.

0035Macrobrachium spp. have even fewer distinct

larval stages, with several zoea, followed by a pl,

then adult. Unusually, the larvae require brackish

water for development, although culture is in fresh

water. This finding was critical in enabling the

development of Macrobrachium aquaculture.

0036Harvest, Handling, and Marketing Harvesting is

dependent, to some extent, on the market require-

ments. Fresh, frozen, or processed crustaceans are

drain-harvested, with the complete crop being re-

moved immediately. This applies to most penaeids,

e.g., P. monodon, crabs (except soft-shell, which are

harvested at molt), and Macrobrachium spp. Most

live products, e.g., freshwater crayfish and some

penaeids (P. japonicus), are harvested in small

batches, typically using baited traps. Harvesting of

crayfish may make use of their rheotactic behavior,

in which the animals self-harvest, by following a

water flow up a ramp into a collection chamber.

0037Crustaceans generally, and prawns in particular,

are typically processed and sold as either frozen

SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans 5249

(cooked, green, whole or tails and as block or indi-

vidually quick frozen), fresh chilled, or as a prepared

or preserved product, e.g., canned. Aquaculture tends

to concentrate on the higher value fresh or frozen

product, to offset production costs. Some species,

notably, Penaeus japonicus, freshwater crayfish, and

some crabs, e.g., Scylla spp., are marketed live

for value-adding or spoilage reasons. Live kuruma

prawn can attract prices of US$75 kg

1

during Japan-

ese holiday periods, justifying the significant extra

harvest, processing and packaging procedures neces-

sary to ensure survival. By contrast, freshwater cray-

fish tend to be marketed live to ensure product quality

at market.

Current Issues and Future Prospects

0038 The principal issues affecting penaeid prawn cul-

ture worldwide are disease and environmental

impacts. The possibility of rapid disease spread in

high-intensity production systems is high, and mor-

tality can be significant. At the individual farm level,

and outwith epidemic-type outbreaks, producers

manage disease risk through quarantine, exclusion

of disease vectors, health testing of stock, and man-

agement of water quality and animal density.

0039 On a larger scale, where entire regions are affected,

disease impacts, particularly viruses, have been cata-

strophic. These outbreaks are harder to manage and

appear to be due to overall pathogen levels in stock,

both broodstock and pl, and the general status of the

culture or external aquatic environment. For example,

the passage of whitespot syndrome virus (WSSV) and

yellowhead disease through Asia can be traced from

the early and mid-1990s. Whitespot alone was con-

sidered to have resulted in losses of US$600 million in

Thailand and in excess of US$2 billion throughout

Asia in 1997.

0040 Similarly, taura syndrome virus and WSSV affected

central and South American production from around

1992.

0041 These diseases occur naturally in the environment,

but significant outbreaks occur when animals are

produced under high-density, sub-optimal conditions.

However, introductions of diseases, for example from

Asia to the Americas, have occurred.

0042 Disease is also a major concern for freshwater

crayfish production given the impact that the fungus

Aphanomyces astaci, or crayfish plague, had on wild

and captive populations in Europe. As a result,

several resistant species have been introduced from

North America, now forming the basis of European

production. The high susceptibility of native Austra-

lian crayfish to the fungus has ensured that strict

quarantine procedures apply to importations of

potential vectors.

0043The environmental impacts of aquaculture, and

particularly prawn farming, have attracted significant

debate in recent years. Largely as a result of unregu-

lated development in Asia and South America, prawn

aquaculture has been linked with coastal ecosystem

destruction, disease outbreaks and introductions, and

unsustainable practices. Consequently, significant

environmental and planning regulations are now

enforced in many countries new to aquaculture,

such as Australia and the USA, and increasingly so

in established aquaculture countries. Regulatory

measures have included limiting farm sizes and

number, control of discharge water quantity and

quality, and the introduction of disease-management

and health-monitoring strategies.

0044The reliance on fish meal and oil for the production

of animal feeds is an issue facing aquaculture. Esti-

mates suggest that fish meal use by aquaculture will

increase from the 35% of total production (6.5 m

tonnes in 2000) to 55% by 2010. In addition, fish-

oil use by aquaculture was 55% of total production in

2000 and is expected to rise to 75% over the same

period. Although mostly used in finfish diets, crust-

acean feeds also contain significant quantities, and

usage should be reduced because of supply-reliability

issues and energy-conversion inefficiency. Substitu-

tion with plant proteins, such as soy, may represent

viable alternatives.

0045Crustacean aquaculture offers significant advan-

tages over traditional wild-capture fisheries, which

are generally in decline or static. The ability to

manage most aspects of aquaculture means that,

theoretically, the environmental impact can be min-

imized, which will be essential for public acceptance

of aquaculture product and practices. Waste-nutrient

management programs, including the use of plants

and animals to lower nutrient concentrations (bio-

remediation), multiple water use for irrigation, and

polyculture will reduce off-farm impacts and improve

production efficiency. Improved feed management,

reduced fish meal usage, and the application of bio-

technology, in the form of genetic selection and man-

agement, should contribute further to cost reduction

and efficiency improvement, enabling aquaculture to

continue its growth.

Nutritional Features of Commercially Important

Shellfish

0046Shellfish are high in protein and unsaturated oils, and

low in cholesterol. They are particularly high in o-3

and o-6 polyunsaturated fatty acids, which are con-

sidered beneficial in reducing high blood pressure,

coronary heart disease, arthritis, and some cancers.

Consequently, nutritionists and medical authorities

have promoted their consumption recently. Table 4

5250 SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans

shows the proximate composition of the important

nutritional components of key cultivated crustaceans.

(See also Table 5 in Shellfish: Commercially Import-

ant Molluscs.)

See also: Shellfish: Commercially Important Molluscs

Further Reading

Bayne BL (ed.) (1991) The biology and cultivation of

mussels. Aquaculture 94(2–3): 121–278.

Fallu R (1991) Abalone Farming. Oxford: Blackwell.

FAO (2001) FAO Yearbook, Fishery Statistics: Aquaculture

Production 1999. Fisheries Series No. 58, vol. 88/2.

Rome: FAO.

Fast AW and Lester LJ (eds) (1992) Marine Shrimp Culture:

Principles and Practices. Developments in Aquaculture

and Fisheries Science, vol. 23. Amsterdam: Elsevier.

Keenan CP and Blackshaw A (1999) Mud crab aquaculture

and biology. In: Australian Centre for International

Agricultural Research, Proceedings No. 78. Canberra.

Landau M (1992) Introduction to Aquaculture. New York:

John Wiley.

Matthiessen G (2000) Oyster Culture. Oxford: Blackwell.

Nettleton J (1985) Seafood Nutrition: Facts, Issues and

Marketing of Nutrition in Fish and Shellfish. New

York: Osprey Seafood Handbooks.

New M and Valenti W (eds) (2000) Freshwater Prawn

Culture. Oxford: Blackwell.

Philips BF and Kittaka J (2000) Spiny Lobsters, Fisheries

and Culture. Oxford: Blackwell.

Primavera JH (1996) Environment friendly aquaculture and

rehabilitation in mangrove ecosystems. In: World Aqua-

culture 96. Annual Meeting of the World Aquaculture

Society Jan. 29–Feb. 2, Bangkok, Thailand.

Shumway SE (ed.) (1991) Scallops: Biology, Ecology and

Aquaculture. Developments in Aquaculture and Fisher-

ies Science, vol. 21. Amsterdam: Elsevier.

Yearsley GK, Last PR and Ward RD (1999) Australian

Seafood Handbook. Canberra: CSIRO Marine Re-

search.

Dietary Importance See Fish: Dietary Importance of Fish and Shellfish

tbl0004 Table 4 Proximate nutritional composition (per 100-g fresh weight) of principal aquacultured crustaceans (sources Nettleton (1985),

Yearsley et al. (1999))

Species Protein (g) Total fat (g) Carbohydrate (g) Energy (kJ) Cholesterol (mg) Fattyacids

(Saturated/monounsaturated/

polyunsaturated/ o-3)

Black tiger prawn

Penaeus monodon

19.2 0.6 (0.4–0.7) 1.8 394 120–160

0.28/0.18/0.34/0.07–0.34

Freshwater

crayfish

Astacus spp.

16.0 0.05 1.0 76 0.21/0.26/0.33/-

Blue crab

Calinectes sapidus

16.2 1.0 (0.4–2.2) 0.6 81 76 0.17/0.22/0.40/0.38

Rock lobster

Panulirus argus

19.2 1.2 1.7 100 106

0.14/0.14/0.59/0.27

General data for penaeids.

o-3 range from other penaeids.

Data for Cherax quadricarinatus.

Data for Cancer Magister.

Cooked product.

SHELLFISH/Aquaculture of Commercially Important Molluscs and Crustaceans 5251

SHERRY

Contents

The Product and its Manufacture

Composition and Analysis

The Product and its

Manufacture

J Bakker, Old Town, Swindon, UK

Introduction

0001 Sherry is the name given to a number of related forti-

fied wines made from grapes grown in Je

rez de la

Frontera, in the province Ca

diz in the south of Spain.

The hot climate of the region would be expected to

produce white grapes which would turn into rather

bland white table wines. However, as a result of a

unique method of maturation, the wines have indi-

viduality and style. White wine made from Palomino

fino, the main grape variety, is fairly neutral, lacking

in acidity and without distinct varietal character. This

neutral base forms an excellent background for the

delicate flavors produced as a result of the maturation

and blending procedures. There are three main types

of sherry, made from the base wine by three different

aging techniques. Sherry can be matured under flor (a

layer of yeasts growing on top of the wine), developing

into fino, or matured without flor yeasts, developing

into oloroso. A combination of flor maturation

followed by a period of aging without flor results in

amontillado. The type of wine making has also been

adopted by other wine-making regions, but the dis-

cussion below will focus on sherry as made in the

demarcated area around Je

rez de la Frontera. The

quality and style of the product depends on many

aspects, such as grapes, viticulture, soil, and climate.

The combination of factors is unique for this region,

making sherry stand apart from these wine styles

made elsewhere. The factors affecting the production

of grapes, the wine making, the maturation, and final

blending of sherry are described.

Grape Production

Climate

0002 The climate in Je

rez de la Frontera is generally warm,

with maximum temperatures in the summer of about



C. Rainfall is moderate and can be variable, but is

generally about 60 cm year

1

. Most rain falls between

November and February, but rain during the vintage

in September is not uncommon. It causes inconveni-

ence in the harvesting of the grapes, but has no effect

on the quality of the grapes. Winters are cool, and

occasionally there is light frost, which tends to occur

when the wines are dormant, and therefore it does not

usually cause any damage. The predominant winds

are southwesterly, and come from the sea and have a

cooling effect while increasing the humidity. The

southeasterly winds are unpopular and are believed

to dry the crop due to a drop in humidity.

Soil

0003The best vineyards consist of rather chalky soils,

known as Albariza, and are situated in the low hills

west of Je

rez de la Frontera. The main merit of the soil

seems to be its associated physical properties: this

soil has good water-absorbing properties and is able

to retain water throughout the very dry summer.

However, the soil goes to a paste-like consistency

when wet, making vineyard access difficult. The soil

dries to a powdery structure, without cracks. The

light color of the soil reflects the heat, and also helps

to prevent the soil from drying out. Irrigation of the

soil is not allowed, but water availability has been

improved by cutting square basins in vineyard slopes

after the harvest. This reduces soil erosion by dimin-

ishing the water flow during the rains.

Vineyards

0004All vines are grafted on rootstocks to avoid infection

by the root aphid Phylloxera. The rootstocks are

hybrids between American and European vines; the

American influence is to confer resistance to the root

aphid Phylloxera. The rootstock should not influence

the flavor of the grapes, but can affect the vigor of the

vine. The very high calcium carbonate in the soil

requires special selection of rootstock, since not all

are able to grow in this type of soil. Young vines start

to produce small quantities of grapes about 2 years

after grafting. A good commercial yield is obtained

after 6 years, and after 25 years the vineyard gives its

maximum production of fine wines. After 30–40

years the yield drops, and when the vineyard is no

5252 SHERRY/The Product and its Manufacture

longer economically viable, the vines are pulled up,

and replanted once the soil has recovered. Currently

only four varieties are allowed to be planted (Palo-

mino fino, Palomino de Je

rez, Muscatel and Pedro

Xime

nez). Palomino Fino is the main variety grown;

this variety yields a much higher crop than Palomino

de Je

rez, which is currently not planted. Only about

2% of the planting consists of Muscatel, grown on

sandy soil, and a little can be used to flavor the wines.

Pedro Xime

nez is used to sweeten wines, and produ-

cers are allowed to buy this outside the demarcated

area. Rows of vines are now planted well apart

(2.3 m), so access with machinery for mechanical har-

vesting is possible, but these are not yet in commercial

use. Vines are generally supported by stakes with two

wires 50 cm and 100 cm above the ground respect-

ively. The vines are pruned low with two short spurs

30–40 cm above the ground. However, low pruning

systems cannot be harvested mechanically. Concerns

exist regarding the possible damage to grapes due to

mechanical harvesting, with negative effects on wine

quality due to expected oxidation problems.

Harvest

0005 The grapes must have a potential alcohol content of

at least 10.5% by volume before they are allowed to

be picked. Generally, 11.5% potential alcohol by

volume and a fairly low acidity (2.75 g l

1

total titrat-

able acidity as tartaric acid) are considered satisfac-

tory. Optimum ripeness is defined as maximum juice

and sugar yield, when the stems start to darken and

the seeds separate easily from the pulp. Since only one

grape variety is grown in a small area, the grapes tend

to ripen all at the same time, and harvesting needs to

take place over a short period. Generally the harvest

starts in the first week of September, and takes no

more than 3 weeks. Since damage to the grapes leads

to the release of polyphenol oxidase, which will cause

browning, care is taken to cause minimal damage to

the grapes. Grape bunches are picked by hand, put in

small containers, and transported to the winery.

Crushing within 4 h of picking will help to prevent

tissue damage and the resulting negative effect on

wine quality. The style of wines depends on the grow-

ing season. In hot years, with drying easterly winds,

the vintage is early, and more oloroso is produced,

while in cooler, more humid years the vintage is

late, and more fino is produced.

Wine Making

Pressing

0006 A number of crushing and pressing methods are used.

Whole bunches are conveyed from the hopper into a

roller crusher by screw conveyor. The stalks help with

the draining of the juice, and are not removed. Press-

ing takes place immediately after crushing, to avoid

juice contact with the skins and the stems. Both batch

and continuous presses are used, and although both

produce good-quality juices, the latter is more eco-

nomical to use due to the lower cost of labor. It is at

this stage that the juice is separated for the intended

wine style to be produced. The free-run juice and the

early pressings containing no more than 200 mg l

1

total phenols (expressed as gallic acid equivalent) are

separated from pressed fractions which contain up to

500 mg l

1

total phenols, while heavily pressed juices

containing more than 850 mg l

1

total phenols are

not suitable to make quality sherry. The solids in the

must are reduced to about 1% before fermentation.

Therefore the juices are usually cooled (12–15



and allowed to settle for 8–18 h to allow the excess

solids to deposit, before being centrifuged. Since the

acidity of the grapes is often low due to the warm

growing conditions, traditionally calcium sulfate was

added to the grapes at crushing, precipitating calcium

tartrate, and apparently liberating free tartaric acid.

Nowadays, an addition of tartaric acid is made to

juices with low acidity to reduce the pH to about

3.45. An addition of about 100 mg l

1

sulfur dioxide

is made to the juice; the amount is varied according to

the condition of the grapes. Sulfur dioxide has a

number of functions and will be more effective at a

lower pH value. It inhibits browning of the juice, thus

protecting its pale yellow color. It also inhibits some of

the undesirable microflora and favors the growth

of fermenting yeasts.

Fermentation

0007Sherry used to be made by fermentation in oak casks,

with a capacity of 500–600 l. Due to the small volume

of fermentations, temperature control was not essen-

tial. Some wines are still made in small casks, to

produce blending wines with a characteristic flavor,

or to season new vats before being used for the

maturation of sherry, or to satisfy the demand from

the Scottish whisky industry for vats seasoned by

sherry. Currently most wine is fermented in large

open cylindrical fermentation tanks, normally with

a capacity between 500 and 1000 hl. Temperature

control in these large tanks is essential, and most

wine is fermented at about 25



C. Commercial yeast

inocula are not normally used, but yeast starters are

often prepared by harvesting some grapes just before

the vintage and allowing the naturally present fer-

menting yeasts to develop. This will help to ensure

that the fermentation vats will start to ferment after

a short time. The initial fermentation is domina-

ted by apiculate yeasts, such as Kloeckera and/or

SHERRY/The Product and its Manufacture 5253

Hanseniaspora, but at the later stage Saccharomyces

cerevisiae (the main fermenting yeast) predominates.

Most of the fermentation will have completed in

about a fortnight, but the fermentation continues

slowly until all the sugar has been depleted. (See

Beers: Biochemistry of Fermentation; Yeasts.)

Classification

0008 By November the fermentation is finished, and the

dry wines have an alcoholic strength of 11–12% by

volume. By that time, lactic acid bacteria naturally

present in the wine have completed the malolactic

fermentation, which converts the fairly sharp-tasting

malic acid into the softer-tasting lactic acid and

carbon dioxide. The wines are initially classified on

the basis of their quality, and fortified accordingly.

However, at this stage it cannot always be predicted

which wines will spontaneously produce flor, which is

a layer of yeasts on the top of the wine and allows

the wine to develop the typical characteristics of

fino sherry. Generally, wines from grapes grown on

soils with high calcium carbonate content in vine-

yards with a cool westerly exposure are likely to

develop flor. Therefore in cooler years more fino-

style wines are produced. Fino is usually made from

the lighter dry wines, made from mainly free run juice

and some light pressings. This wine has a pale yellow

color, low total phenols (200 mg l

1

), a good pungent

aroma, a volatile acidity between 0.3 and 0.5 g l

1

(expressed as acetic acid), and is free of any bacterial

spoilage. These wines usually develop flor spontan-

eously. Oloroso is usually made from slightly darker

wines, with higher concentrations of total phenols

(up to 475 mg l

1

), which are less likely to develop

and support flor. These base wines have a more

vinous and full-bodied nose and a higher volatile

acidity (0.7–0.9 g l

1

). Wines made from the higher

pressings and subsequently with higher total phenols

(over 550 mg l

1

) are classed as raya wines, but also

belong to the oloroso style.

Fortification

0009 After fermentation the wines usually clarify spontan-

eously, and just after their classification they are

racked of their lees (the deposit of yeast cells, and

lactic acid bacteria from the malolactic fermenta-

tion). At that time the wines are fortified with fortify-

ing spirit, which is almost neutral in character. The

fortifying spirit makes little direct contribution to

the sensory characteristics of the wine, but it will

affect the maturation of the wine. It is prepared by

distillation of wine and wine byproducts such as lees

and pomace (the left-over solids after pressing the

grapes). It has a strength of at least 95% by volume.

The fortifying spirit is also produced outside the

sherry region and is usually produced in the La Man-

cha area in central Spain. Fino and oloroso wines are

fortified 15.5% alcohol by volume, while raya wines

are fortified to 18.5% alcohol by volume. Before

adding the fortifying spirit it is mixed with an equal

quantity of wine, and allowed to settle for about 3

days. The half-strength spirit is used to fortify the

wines, and causes much less clouding of the wine

than the undiluted spirit would have done.

Maturation

0010Wines are stored in bodegas, which are tall, well-

ventilated buildings, designed to stay relatively cool,

especially from the ground level to about 2 m above

the ground. The wines are matured in seasoned oak

casks, with a capacity of 500–600 l, and organized to

simplify fractional blending. The wine can either be

matured under flor, and develop the typical fino char-

acter, or matured without flor to develop oloroso

wines. The wines will be allowed to mature un-

blended for about a year, and a collection of wines

all from one year is referred to as an

ada. Young fino

wines are kept in vats only 80% full, providing a

relatively large wine–air interface on which flor can

develop, and may need frequent topping up to main-

tain the wine level. They are kept at a uniform tem-

perature in the cooler part of the bodega, and the

alcohol is maintained between 14.5 and 15.5% by

volume. The casks are disturbed as little as possible,

to prevent any damage to the layer of flor. Young

oloroso wines, which did not develop much or any

flor, are fortified to 18.5%, which inactivates any flor

yeast and prevents flor from being formed. The casks

are kept 95% full and their storage temperature is less

critical than for the fino wines. Raya wines will be

matured at higher temperature, often by storing them

outside in the sun, and the losses in wine as a direct

result of evaporation can be substantial. They will

develop into dark wines and can be blended with

olorosos, or develop into oloroso-style wine them-

selves. In order to obtain large quantities of wines

with a consistent quality, an elaborate fractional

blending system is used, referred to as a solera system.

The sherries from the an

ada will gradually be fed into

a solera system.

Flor

0011The wines with low total phenol contents suitable to

become fino-style wines will spontaneously develop a

wrinkly film of yeast on the surface of the wine. The

composition of the wine determines whether a vigor-

ous flor is able to develop. There is still a debate

regarding the origin of the flor yeasts and their tax-

onomy, although a number of the flor yeasts belong to

5254 SHERRY/The Product and its Manufacture

the Saccharomyces species. However, the yeasts are

physiologically different from the fermenting yeasts

dominating during the fermentation. The fortifica-

tion of the wines to 15.5% alcohol (by volume) in-

hibits film-forming acetic acid bacteria, which would

spoil the wine. Development of flor depends on the

temperature, and wines should be stored between 15

and 20



C. The activity of the flor depends on the

season; the flor is most active between February and

June, and then declines until October time, when

activity increases again. The flor protects the wine

from the uptake of oxygen, and prevents oxidative

browning, to which the wine is very susceptible. The

growing flor will consume any dissolved oxygen

and protects the wine from absorbing oxygen from

the head space in the cask. This lack of oxygen in the

wine prevents the oxidation of phenols, hence fino

maintains a pale yellow color. The flor also results in

numerous biochemical changes, which greatly influ-

ence the character of the wine. There is a slow de-

crease in volatile acidity, a reduction in glycerol, and a

reduction in alcohol, which is used as a carbon source

for flor yeast growth. There is a significant increase in

acetaldehyde, normally to 260–360 mg l

1

. Acetalde-

hyde contributes to the typical, somewhat apple-like

nose of fino wines. Possibly autolysis (spontaneous

rupture of old yeast cells, thus releasing their con-

tents) of the yeast cells which form part of the sedi-

ment on the bottom of the cask may well contribute

to the typical flavor. The film should not be disturbed;

however, the blending system is crucial to maintain

the flor. Small volumes of wine have to be taken out

frequently, and replaced with fresh wine from the

ada to renew the oxygen supply and renew nutri-

ents for flor maintenance. Specific wine transfer tech-

niques have been established to transfer the wine with

minimal disturbance of the flor in order to maintain

the flor and to achieve the blending.

Maturation without Flor

0012 In order to produce a good oloroso, the neutral base

wine needs to contain sufficient oxidizable phenols,

and is therefore not suitable for fino wines. Fortifica-

tion to 18.5% alcohol by volume avoids the growth

of any flor. Wines are stored in warmer parts of the

bodega and under oxidative conditions. The dark

golden color of the oloroso can be attributed to oxi-

dation of phenols. Although the wines are fermented

to dryness, the glycerol formed during alcoholic

fermentation (7–9gl

1

) gives a hint of sweetness on

taste. A considerable loss in volume during matur-

ation and usually an increase in alcoholic strength

have been reported in oloroso wines, resulting in a

higher concentration of nonvolatiles. The volatile

acidity and the concentration of ethyl acetate increase

also, in part as a concentration effect and in part

formed by oxidation and esterification. The higher

alcohol concentration, often combined with a higher

storage temperature, may lead to increased extraction

of phenols from the wood during maturation of olor-

osos, explaining the higher concentrations of phenols.

Oloroso takes a long time to develop and requires

about 7–8 years of maturation.

Maturation With and Without Flor

0013Some wines mature initially under flor, and develop

all the characteristics of a fino. However, when the

wines are not refreshed with additions of younger

wines in the solera system, or when the wine has

reached a considerable age, the wine may start to

lose the flor. Further fortification to about 17.5%

alcohol by volume is usual, to protect the wine

against spoilage by acetic acid bacteria and pre-

vent any further development of flor. The wine is

matured in a second solera system in casks which

are 95% full, and the aging processes change, with

oxidation of the wine changing the pale yellow color

to amber and dark gold, together with the develop-

ment of a nutty, complex flavor typical for this wine,

called amontillado. It takes at least 8 years to trans-

form a fino into an amontillado, and genuine amon-

tillados may have gone through three fino solera

systems (which may be between 18 and 21 criaderas)

and an amontillado solera system (5–8 criaderas).

Solera System

0014The solera system contains blends of wines of differ-

ent ages and vintages, and aims to mature wines to

achieve a steady supply of wine of comparable and

consistent quality. The blending procedure to which

the solera system is subjected is very complex. Some

of the oldest wine is frequently taken out, and pre-

pared for shipping. Wine from the previous stage

is used to replace the oldest wine taken out, and

the topping-up of older wines with younger wines

continues throughout the solera system, until the

youngest stage is reached; this is then replenished

with a suitable an

ada wine. Wine in the last stage

of the solera system is usually called solera, while

the other wines at various stages of blending and

maturity are referred to as criaderas. Since the fino

wines are most variable in composition, they tend to

need the largest number of blending stages or cria-

deras. Careful management of the system is needed to

ensure that a continuous flow of wine with the

required quality characteristics is obtained. The

ada wine, with which the solera system is topped

up, is carefully selected based on analysis and tasting,

but there will be some differences in composition

from year to year. A typical solera system with flor

SHERRY/The Product and its Manufacture 5255

maturation may consist of five criaderas and a solera,

each stage comprising 100 casks. The maturity of the

wine in the casks increases progressively, with wines

in the fifth criadera being the youngest. Typically

upto 25% of the wine in a fino solera is moved

every 3 months. Less frequent withdrawals of larger

volumes tends to hinder the development of the flor.

However, in order to meet seasonal demand, the

withdrawals need to be made at somewhat irregular

intervals.

Coloring Wines

0015 Special coloring wines are prepared, which also

impart flavor to the blend. Grape must is concentrated

by boiling down, which heavily caramelizes the must.

This concentrate is added to fermenting must made of

the last pressing of Palomino fino grapes, in a suffi-

cient quantity to stop the fermentation at about 8%

alcohol by volume. After about 3 months the wine is

racked, fortified to 15–17% alcohol by volume, and

matured in an oxidative solera system. A number of

food caramels are also allowed for use in sherry. (See

Caramel: Properties and Analysis.)

Sweetening Wines

0016 A number of different sweetening wines are prepared.

One is made from fortified free-run juice, which is

racked, fined, and matured before use. A wine with

more character (dulce pasa) is made by drying the

bunches of Palomino grapes for 2 weeks in the sun.

The juice is fortified to 17.5% alcohol by volume, and

the wine is matured in a solera system, where it

develops a deep golden color and raisin-like flavors.

This dulce pasa is increasingly used, since it can be

made more economically than the traditional

sweetening wine made from Pedro Xime

nez grapes.

Pedro Xime

nez wines have flavors which contribute

to the character of blended sweet sherry. Pedro Xime

nez grapes are dried in the sun for up to 20 days,

until they have doubled in sweetness. During this

process they develop a characteristic dark color and

flavor, reminiscent of a rich Christmas cake. The

grapes are pressed and the juice is fortified to about

9% alcohol by volume. Pressing these very dry grapes

is difficult, and occasionally fresh grapes are added to

aid the pressing. The Pedro Xime

nez wines are usu-

ally matured in an oxidative solera system. Pedro

Xime

nez wine can be imported from the Montilla

district, where the hotter climate lends itself better

to the production of the grapes. Rectified concen-

trated grape musts, which are almost colorless and

odorless, are also widely used to obtain pale cream

sherries, by sweetening fino wines without altering

their delicate flavor.

Volatile Compounds

0017The volatile compounds in sherry can be derived

from the grapes, formed during the fermentation or

maturation. It is during this last stage, especially

when maturation under flor is used, that the aroma

typical for the style of sherry is formed, and hence

forms the most important stage for the formation of

volatiles typical for sherry. Sotolon (4,5-dimethyl-3-

hydroxy-2(

H)-furanone) has been identified in

sherry matured under flor only; it is present in suffi-

cient concentrations to lend its nutty odor to the

characteristic aroma of flor sherry. Solerone

(4-hydroxy-5-ketohexanoic acid lactone) has been

reported to contribute an aroma of premium-quality

Pinot noir wine. Oak lactone (trans-3-methyl-4-

hydroxyoctanoate acid lactone) extracted during

maturation in oak gives a distinct woody note to

sherry, and has also been found in other alcoholic

beverages matured in oak. (See Flavor (Flavour)

Compounds: Structures and Characteristics.)

Commercial Styles

0018The end products have very complex sensory charac-

teristics. Sherry is fermented to dryness, and fino

sherries are usually marketed dry. Finer and older

wines can also be sold dry, but most of the wines are

sold sweetened. Fino has a pale straw color, and is

very dry but without acidity. Its bouquet is delicate

yet pungent and the alcoholic strength usually lies

between 15.5 and 17% by volume. Manzanilla, pro-

duced in the coastal town Sanlu

car de Barrameda, is a

regional variation of the fino style, which has a deli-

cate and highly individual aroma. It is very dry, with a

clean and slightly bitter aftertaste, being slightly less

full-bodied than fino. Manzanilla has a pale straw

color much like a fino, and an alcoholic strength

between 15.5 and 16.5% by volume. Amontillado is

very dry and clean, with a pungent aroma reminiscent

of fino but nuttier and fuller-bodied. The color is

amber, and becomes darker with increasing age. The

alcoholic strength is 17–18% by volume. Oloroso

has a strong bouquet, being less pungent than fino

or amontillado, but with more body, sometimes

referred to as fatness. The sherries are dry, but have

a sweet aftertaste. Oloroso has the darkest color, best

described as dark gold, and its color intensity in-

creases with age. Wines marketed as medium dry,

medium, cream, or pale cream sherry are usually

based on oloroso wine, with an addition of fino to

lighten the color and flavor and a small amount of

amontillado. The choice of sweetening and coloring

material depends on the required end product. Pedro

Xime

nez is often added to round the flavor of the

blend.

5256 SHERRY/The Product and its Manufacture