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

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follows: total nitrogen 1.6%, reducing sugar 4%,

sodium chloride 19% or more, respectively.

0076 Acid hydrolysis of plant protein for soy sauce

manufacture was forbidden by law in China 1979,

because the contents of arsenic acid and hydrochloric

acid were too high.

0077 Taiwan The annual production of soy sauce in

Taiwan was estimated to be 12 000 kl in 1994,

which is equivalent to 6 l per capita per year.

0078 About 80% is the so-called tou-yu, and this is made

from soybeans and wheat originating from China.

There were 433 soy sauce manufacturing plants in

Taiwan in 1978, of which the eight largest producers

comprised at least 45% of local market. Soy sauce

products include genuine fermented soy sauce (25%),

chemically hydrolyzed soy sauce (5%) and blended

soy sauce (70%). There are three national standard

grades of soy sauce in Taiwan, and their total nitrogen

percentages were 1.4, 1.1, and 0.8 g per 100 ml,

respectively, in 1994.

0079 Five to 10% of Taiwan soy sauce is estimated to be

in-yu, which is made only from black soybeans and

very much resembles Japanese tamari, made only

from yellow soybeans. The black soybean koji is

washed with water, before being mixed with salt

water to make a mash so as to remove the bitter

taste of the product.

0080 Fermented soybean sauce similar to in-yu and

tamari is also produced in the southern part of

China and seems to be the prototype of the soy

sauce prepared only from soybeans. Tamari mash is

fermented usually in wooden kegs in Japan, but the

soybean sauce in Taiwan, Thailand, Singapore, Ma-

laysia, Indonesia, and the southern part of China is

fermented in China jars (approximately 150 l in

volume) and in the sunshine.

0081 Korea The annual production of soybean sauce in

Korea was 420 000 kl in 1996, which included

180 000 kl of industrially produced soy sauce and

240 000 kl of home-made product. The fermented

soy sauce produced industrially in Korea is of the

Japanese koikuchi type, but about 70% of its produc-

tion is estimated to be chemically hydrolyzed soy

sauce. The home-made soy sauce is prepared by a

traditional method, in which cooked soybeans are

mashed and made into small balls, which are dried

in the sun during the day and kept warm at night for

several days in the winter. Molds grow on the surface

of the balls and penetrate the interior of the balls,

which are then called ‘meju.’ Sufficiently dried meju

is packed in a rice-straw bag for aging for a few

months. The aged meju balls are then placed into

brine and kept in large China jars in the sunshine for

several months for fermentation. The ripened meju–

brine mixture is separated into supernatant liquid and

sediment residue. The liquid is soy sauce, and the

residue is soybean paste, which is sometimes mixed

with red pepper. In recent years, better-quality meju

has been prepared industrially, in which cooked soy-

beans are inoculated with Aspergillus oryzae mold in

a controlled fermentation room. Housewives take the

improved meju home and add it to brine to make soy

sauce and paste.

0082Other countries In Singapore, Malaysia, and Indo-

nesia, two types of soy sauce are manufactured: a

light soy sauce (in Cantonese ‘sung-show’ or in Hok-

kien ‘chiuw-cheng’), and a dark soy sauce mixed with

cane molasses (in Cantonese ‘low-chow’ or in Hok-

kien ‘tau-iu’). In Indonesia, soy sauce is called ‘keit-

jap’ or ‘kecap,’ and similarly, two types of kecap are

popular in Sumatora and the latter in Java.

0083The per capita daily consumption of kecap in Indo-

nesia is 10–15 ml. The kecap mash is washed with salt

water twice and the mixed extract is concentrated

in the sun. The residue from the extraction is used

for tauco or miso of an inferior grade, but the genuine

tauco is made from soybeans and wheat flour cul-

tured with Aspergillus oryzae mold. The molded-

cultured material, or ‘koji’, is dried in the sun,

mixed with salt water, and fermented and concen-

trated in the sun for 3–7 weeks. Tauco is a slurry

containing 10% protein, and is sold in glass bottles,

thus differing from Japanese miso, which is a paste

containing 25% protein. In the aforementioned coun-

tries the chemical acid hydrolysate of soybeans and

the semichemical or shinshiki soy sauce are also

popular, but the amount of extract produced is not

known.

See also: Browning: Nonenzymatic; Carbohydrates:

Classification and Properties; Fatty Acids: Properties;

Lactic Acid Bacteria; Mycotoxins: Occurrence and

Determination; Phenolic Compounds; Phospholipids:

Properties and Occurrence; Protein: Chemistry;

Digestion and Absorption of Protein and Nitrogen

Balance; Soy (Soya) Beans: The Crop; Processing for the

Food Industry; Starch: Structure, Properties, and

Determination; Wheat: The Crop; Grain Structure of

Wheat and Wheat-based Products

similar products.

0028Kefir (Caucasus) made with kefir grains.

0029Artificial preparations, e.g., kefir made

without grains.

2370 FERMENTED MILKS/Types of Fermented Milks

3.0030 Mixed material plant–milk fermentations

3.1.

0031 Products where plant material is a substrate

for fermentation

0032 Kishk (Middle East), niyogurt (Philip-

pines).

3.2.

0033 Products where plant material is claimed to

be a carrier of specific microorganisms and/

or enzymes.

0034 Nordic ropy milks.

0035 Various unclassified fermented milks.

0036 Buttermilks

5.1.

0037 Conventional cultured buttermilk, a bypro-

duct of cultured butter manufacture.

5.2.

0038 Cultured buttermilk obtained by fermenta-

tion of a sweet buttermilk.

5.3.

0039 Yogurt buttermilk obtained by churning

yogurt into butter and a liquid byproduct

0040 Cultured creams

The major classes of fermented milks and their inter-

relationships can be graphically presented in the form

of a ‘tree of fermented milks’ (see Figure 1), which

shows the diversity of these products, further enriched

by various physical forms in which fermented milks

can be offered to consumers.

0041There are many variations and modifications to

these products in different parts of the world, which

usually reflect local traditions as well as continuous

efforts to develop new products. For example, various

types of fermented whey beverages have gained popu-

larity in some European countries.

Taxonomic Location of Starter Cultures

0042The main thermophilic bacteria used in the produc-

tion of fermented milks include lactobacilli, Strepto-

coccus thermophilus and bifidobacteria. DNA

fingerprinting is now commonly used to determine

the taxonomic location of these organisms. As a

result, important changes have been made to the

taxonomic status of certain well-known starter bac-

teria. For example, organisms previously classified as

Lactobacillus acidophilus are now divided into the

following six species: Lb. acidophilus, Lb. crispatus,

Lb. gasseri, Lb. amylovorus, Lb. gallinarum,and

Lb. johnsonii. Similarly, the lactobacilli previously

classified as Lactobacillus casei are now located

within either Lb. rhamnosus or Lb. paracasei ssp.

paracasei. The extensively studied and well-publi-

cized Lactobacillus GG is now a strain of Lb. rham-

nosus.

0043The main organisms used in mesophilic starters

belong to Lactococcus lactis (with subspecies lactis

and cremoris) and Leuconostoc spp. Yeasts,

belonging mainly to Saccharomyces spp., and molds

such as Geotrichum candidum, are also included in

some mesophilic starter cultures.

Manufacturing Technology

0044Manufacture of fermented milks consists of several

basic steps. Most fermented milks can be produced

as either ‘set’ or ‘stirred’ products, and this feature

determines the sequence of major operations (see

Figure 2).

Preparation of Milk

0045Milk for production of fermented milks should

comply with the following requirements: low bacter-

ial counts, absence of pathogenic organisms and ab-

sence or very low concentrations of various inhibitory

substances that may find their way into milk, such as

residues of antibiotics from the treatment of mastitis,

residues of dairy sanitizers, etc.

0046The first step in milk preparation is usually the

clarification of milk, to remove mechanical impurities

and somatic cells. This operation is carried out in

centrifugal clarifiers/separators, but filtration of raw

milk can also be used for this purpose.

Mixed lactic and

alcoholic

fermented milks

Kefir

Cultured

buttermilk

Yogurts

Liquid

Pasty

Jellified

Frozen

Foamy

Dried

Cultured milks

with selected

intestinal bacteria

Mixed material

plant−milk

fermentations

Various unclassified

fermented

milks

Concentrated

fermented milks

Scandinavian

fermented milks

with mesophilic

bacteria

fig0001 Figure 1 Tree of fermented milk types. From J.A. Kurmann

(1984) Aspects of the production of fermented milks. In: Fer-

mented Milks ^ Proceedings of an IDF seminar in Avignon, pp. 16–

26. International Dairy Federation Bulletin No. 179. Brussels:

International Dairy Federation (1984), with permission.

FERMENTED MILKS/Types of Fermented Milks 2371

0047 The milk has to be standardized, i.e., its compos-

ition altered to meet legal requirements and/or to

improve the economy of production and/or to modify

the characteristics of the final product. Usually, stand-

ardization means adjustment of fat content and

sometimes also of nonfat solids (NFS) content. NFS

content in milk can be increased by (1) evaporation,

which usually removes 10–20% water, (2) addition of

skim milk powder, or (3) addition of milk concen-

trate. Membrane filtration, especially ultrafiltration

(UF), is increasingly being used to concentrate milk

for production of yogurt and various other fermented

milks. The main advantages of using UF retentates in

production of fermented milks are: (1) enhanced vis-

cosity; (2) reduced syneresis (even at lower fat con-

tent); (3) increased product yield (in manufacture of

concentrated fermented milks) due to a partial reten-

tion of whey proteins; and, quite often, (4) better taste

due to the absence of ‘chalkiness’ frequently associ-

ated with the use of milk powder.

0048 Many fermented milks, including yogurt, can be

made from reconstituted or recombined milk. This

technique has obvious advantages in locations

where it is difficult to obtain raw milk of a consist-

ently high microbiological standard. However, fer-

mented milks made from a totally reconstituted or

recombined milk account for only a small fraction of

the total production of fermented milks.

0049 The next manufacturing step is homogenization of

milk, which, by reducing the diameter of the fat glob-

ules, prevents fat separation and has a whitening

effect on the milk. Homogenization also improves

(1) the stability of fermented milks during storage

(by reducing syneresis) and (2) their rheological

properties. The usual conditions of homogenization

are 10–20 MPa at 50–60



C. Higher temperatures are

sometimes used, e.g., 65



C in production of filmjo

lk,

a Scandinavian fermented milk.

0050Homogenization is followed by heat treatment,

in order to: (1) pasteurize the product; (2) make the

milk a more nutritious growth medium for the

starter organisms, through the release of amino

acids and other growth factors, reduction of the

redox potential and elimination of inhibitory sub-

stances; (3) improve physical properties of fermented

milks and reduce syneresis; and (4) prevent formation

of rancidity through inactivation of lipases. To

achieve these objectives, it is common practice to

batch-pasteurize milk at 80–90



C for 20–30 min.

Heating of milk to the required temperature in a

plate or tubular heat exchanger is followed by

pumping into a holding unit where the temperature

is maintained for the predetermined period. In some

plants, milk is heated in a continuous process in a

closed system at 90–95



C for 5 min or more. Heat

exchangers are also used to cool milk to the fermen-

tation temperature. In cases where the only objective

of heat treatment is pasteurization of milk, high-

temperature, short-time (HTST) pasteurization is

usually used.

0051Another step recommended in manufacture of

some fermented milks is the deaeration of milk,

which is said to reduce syneresis and improve the

consistency of the final product.

Standardized milk

Homogenization,

pasteurization

Batch heat treatment

Batch inoculation

Filler

Cooler

Incubation room

(20−45 ⬚C)

Cold storage

(<7 ⬚C)

Market

Batch heat treatment

Starter culture

Incubation vessel

20−45 ⬚C

Starter culture

Set fermented milks

Stirred fermented milks

fig0002 Figure 2 Basic steps in manufacture of fermented milks. From International Dairy Federation (1988) Fermented Milks ^ Science and

Te c h n ol o g y . International Dairy Federation Bulletin No. 227. Brussels: International Dairy Federation, with permission.

2372 FERMENTED MILKS/Types of Fermented Milks

Preparation of Starters

0052 Starters for the commercial production of fermented

milks can be prepared in several different ways,

depending on the type of final product and the type

of manufacturing facilities. The majority of fermented

milks are now made with defined starters, but for the

production of some traditional fermented milks, for

example kumys and leben, undefined starters are usu-

ally used. In these starters, various lactic acid bacteria

and yeasts remain in a protocooperative and possibly

also a symbiotic relationship. Traditionally, a starter

was a residue from the previous batch that was added

to suitably prepared milk. Nowadays, such starters

are propagated aseptically in the laboratory to serve

as an inoculum for the bulk starter unit.

0053 The majority of fermented milks are made with

multiple-strain starters, which are defined mixtures

of two or more strains. Apart from enabling manu-

facturers to make better-quality products, multiple-

strain starters can cope better with bacteriophage

challenge if suitable bacteriophage-unrelated strains

are selected, though this may not always be feasible.

A few types of fermented milks are made with defined

single-strain starters. Milks fermented with selected

intestinal bacteria belong to this category, e.g., yakult,

made with Lactobacillus paracasei ssp. paracasei (for-

merly known as Lactobacillus casei strain Shirota),

and acidophilus milk, made with Lb. acidophilus.

0054 The importance of the physical characteristics of

fermented milks is reflected in the use of microorgan-

isms which synthesize a glycocalyx, a polysaccharide

or glycoprotein material which forms ‘capsules’

around the cells that produced it. Such capsules,

sometimes referred to as ‘slime’ or ‘mucus’, act as a

stabiliser in the product, improving viscosity, disguis-

ing syneresis of the milk protein gel, and making the

product less susceptible to thixotropic phenomena.

Capsule-forming organisms are incorporated into

multiple-strain starters used in the manufacture of

many types of fermented milks.

0055 In the conventional starter preparation methods,

several subcultures in the laboratory are needed to

produce, from the initial freeze-dried or liquid culture,

the inoculum volume required for the bulk starter

unit. This time-consuming step needs skilled person-

nel to ensure effective quality assurance at all stages

of starter preparation. Because of demands on man-

power, space and capital, many manufacturers of

fermented milks, rather than preparing their own

starters, prefer to rely on concentrated commercial

starters, which contain up to 10

cells per ml and

can be added to the bulk starter unit or directly to the

production tank or vat (conventional starters may

contain up to 10

cells per ml). Concentrated starters

are available in either deep-frozen or freeze-dried

form.

0056Starter cultures selected for the manufacture of

fermented milks should not produce appreciable

amounts of lactic acid in the product during refriger-

ated storage. Postfermentation acidification usually

leads to product defects such as syneresis of the pro-

tein coagulum and the consequent expulsion of whey.

Fermentation

0057The temperature and time of fermentation can be

varied to influence the final product characteristics.

The fermentation temperature usually does not differ

much from the optimal growth temperature of the

starter organisms. It is essential that the temperature

remains constant during fermentation. Sometimes, in

order to improve the physical properties of the final

product, manufacturers choose a lower temperature

and a longer time of fermentation to promote the

formation of mucoidal capsules by some starter bac-

teria. For the stirred product, fermentation is carried

out in the production tank or vat; the ‘set’ product is

fermented in retail containers.

Cooling

0058Fermentation is terminated by cooling which,

depending on whether the product is stirred or cup-

set, can be achieved by different techniques. Cooling

of the product, usually to refrigeration temperature,

allows the manufacturer to control acidity and initi-

ate the ‘cold gelation’ of the curd at the appropriate

time. The cooling rate is often critical to the quality of

the product and is usually determined empirically by

each manufacturer. In general, manufacturers aim to

lower the temperature of the ‘set’ product to < 10



as quickly as possible, and then continue cooling it at

a slower rate to the storage temperature.

0059In the manufacture of stirred fermented milks,

cooling is often carried out in two stages: at first to

approximately 20



C, at which point the flavor ingre-

dients are added, and the product is packaged into

retail containers, and second to the refrigeration tem-

perature. The second stage of cooling is often con-

ducted at a slow rate and may take up to 12 h. This

method is said to result in improved rheological

characteristics of the product.

Flavoring

0060Fermented milks are often flavored by the addition

of fruit pulp or pure

e or other flavoring ingredients.

Fruit pulp, with a sugar content of approximately

60%, is usually added at the level of about 10%.

Pectins present in fruits exert a stabilizing effect on

the product, but additional stabilizers may be added

FERMENTED MILKS/Types of Fermented Milks 2373

to the product at this stage. These include high-

molecular-weight compounds such as gelatin, or vari-

ous hydrocolloids of plant origin (‘gums’), including

compounds derived from some seaweeds. For the

stirred product, flavoring ingredients are added after

or during the cooling stage, whereas the flavoring of

the ‘set’ product is carried out prior to fermentation

and filling into retail containers.

Packaging

0061 Fermented milks are packed in containers imperme-

able to water and odors, insoluble in water, and free

from foreign odors. In some applications, imperme-

ability to light, and low permeability to oxygen are

also required. Glass, often dyed to reduce the effect of

light on the product, was used for a long time as a

packaging material for fermented milks, but has now

been almost totally replaced by synthetic materials

and paper coated with various polymers such as poly-

ethylene. The paper carton, usually formed into a

rectangular container, can also be impregnated with

resins and/or coated with aluminum or silicone. Syn-

thetic materials (‘plastics’) are light and can be easily

molded into light-weight containers of diverse shapes.

The cup is the most common shape of container, but

bottles and pouches are also used. Containers for

products containing still-viable yeast cells may have

a three-layer lid that allows the escape of carbon

dioxide generated during storage.

Regulatory Aspects

0062 Fermented milks offered for sale must conform to

legal requirements, which, apart from setting micro-

biological quality standards to safeguard public

health, usually define the chemical composition of

the product, its shelf-life and, in many cases, the

number of viable cells of starter bacteria that must

be present in the product at the point of sale. In Japan,

for example, a product classified as fermented milk or

‘lactic milk drink’ must contain at least 10

viable

cells of lactic acid bacteria and yeasts per milliliter.

Standards for fermented milks in some countries in-

clude the requirement for the live cells to be present in

the product at the end of its shelf-life (declared on the

package as the ‘use-by’ date) but do not specify the

minimum numbers. The compositional requirements,

usually specified as the minimum content of NFS and

fat, differ widely between countries.

0063 The final acidity is often included in the standards

as (1) the minimum concentration of lactic acid,

(2) the minimum titratable acidity according to an

arbitrary scale, e.g., degrees Soxhlet–Henkel (



SH),

Dornic (



D), or Tho

rner (



Th), or (3) the maximum

pH of the product.

0064Products universally known, such as yogurt, are

subject to fairly detailed regulations, whereas less

well-known products may not have legally binding

standards of identity and have to comply with require-

ments set for other products deemed similar for pur-

poses of control by relevant government authorities.

Health-related Claims

0065Traditions of folk medicine in many parts of the

world have endorsed fermented milks as beneficial

not only in the prevention of various health disorders

but, sometimes, also as an aid in treatment of these

disorders. In addition to traditional products, fer-

mented milks made with ‘probiotic’ cultures have

expanded the range of claimed health benefits. For

some of these effects, it would be difficult to separate

the effect of starter organisms alone from that of milk

fermented with these organisms.

0066Studies of human intestinal flora are fraught with

methodological difficulties. It is not easy to obtain

samples of intestinal contents that would accurately

reflect quantitative and qualitative relationships in

the gut. In addition, the microbial population of the

gut is rather stable in healthy individuals and is not

affected by the diet. Lactobacilli and bifidobacteria

ingested with the diet do not supplant existing

intestinal bacteria. However, sufficiently rigorous evi-

dence has now been gathered to suggest that in some

disease states, consumption of fermented milks may

benefit the host.

0067In general, health benefits claimed for many types

of fermented milks refer to their effect on (1) the

microbial ecology of the gut and/or (2) specific ail-

ments unrelated to the gut ecology. Health claims in

both these categories include:

0068immunomodulatory effects, including enhance-

ment of antitumor activity;

0069antimutagenic properties;

0070stabilization of gut mucosal barrier, which may

lead, among other things, to suppression of allergic

reactions;

0071prevention and treatment of diarrhea caused by

rotavirus and bacterial infections;

0072alleviation of radiotherapy-induced diarrhea;

0073restoration of normal ecological relationships in

the gut after antibiotic treatment;

0074alleviation of constipation;

0075inhibition of pathogenic organisms;

0076alleviation of lactose intolerance;

0077lowering of serum cholesterol;

0078antihypertensive effects.

It would be reasonable to expect that relationships

in the gut can be influenced primarily by the

2374 FERMENTED MILKS/Types of Fermented Milks

thermophilic organisms ingested with fermented

milks. Beneficial properties of the mesophilic bacteria

would be due to their metabolites present in the prod-

uct before they are consumed, rather than to any

lasting effect on the microflora of the gut. In this

context, it is interesting to note that an organism

known as Lactococcus lactis L1A, isolated from

samples of fermented milks produced on farms in

northern Sweden, was recovered from fecal samples

up to 15 days after the consumption of fermented

milk containing it had ceased.

0079 During the past few decades, there has been a

noticeable revival of popular and scientific interest

in ‘probiotic’ microorganisms and fermented milks.

Many of the health benefits claimed for these

microorganisms and products still remain to be

substantiated by unequivocal experimental and/or

epidemiological evidence.

See also: Cheeses: Chemistry of Gel Formation; Flavor

(Flavour) Compounds: Structures and Characteristics;

Functional Foods; Homogenization; Lactic Acid

Bacteria; Milk: Processing of Liquid Milk; Packaging:

Packaging of Liquids; Probiotics; Recombined and

Filled Milks; Starter Cultures

Further Reading

Bottazzi V (1983) Other fermented dairy products. In: Reed

G (ed.) Biotechnology: Food and Feed Production, vol. 5,

pp. 315–363. Verlag Chemie, Weinheim.

International Dairy Federation (1984) Fermented Milks –

Proceedings of an IDF Seminar in Avignon. Inter-

national Dairy Federation Bulletin No. 179. Brussels:

International Dairy Federation.

International Dairy Federation (1988) Fermented Milks –

Science and Technology. International Dairy Federation

Bulletin No. 227 Brussels: International Dairy Feder-

ation.

International Dairy Federation (1996a) Nutrition News-

letter No. 5. Brussels: International Dairy Federation.

International Dairy Federation (1996b) The World Dairy

Situation 1996. International Dairy Federation Bulletin

No. 314. Brussels: International Dairy Federation.

Kosikowski FV and Mistry VV (1997) Cheese and Fer-

mented Milk Foods, Origins and Principles, 3rd edn,

vol. I. Westport, CT: FV Kosikowski, L.L.C.

Kurmann JA, Rasic JLJ and Kroger M (1992) Encyclopedia

of Fermented Fresh Milk Products. New York: Van

Nostrand Reinhold.

Litopoulou-Tzanetaki E and Tzanetakis N (1999) Fer-

mented milks – range of products. In: Robinson RK,

Batt CA and Patel PD (eds) Encyclopedia of Food Micro-

biology, pp. 774–784. London: Academic Press.

Marshall VM (1987) Fermented milks and their future

trends. I. Microbiological aspects. Journal of Dairy

Research 54: 559–574.

Nakazawa Y and Hosono A (eds) (1992) Functions of

Fermented Milk – Challenges for the Health Sciences.

London: Elsevier Applied Science.

Robinson RK (ed.) (1991) Therapeutic Properties of Fer-

mented Milks. London: Elsevier Applied Science.

Tamime AY and Robinson RK (1988) Fermented milks and

their future trends. II. Technological aspects. Journal of

Dairy Research 55: 281–307.

Tamime AY and Robinson RK (1999) Yoghurt: Science and

Technology, 2nd edn. Boca Raton, FL: CRC Press.

Wood BJB (ed.) (1992) The Lactic Acid Bacteria in Health

and Disease. London: Elsevier Applied Science.

Products from Northern Europe

H Roginski, University of Melbourne, Werribee,

Victoria, Australia

Introduction

0001Fermented milks have always played an important

role in the nutrition of people inhabiting northern

Europe. In Scandinavia in particular, consumption

of fermented milks has a long tradition. Historically,

fermented milks, often referred to as sour milks, were

made and consumed at home. Most of these products

have a characteristic thick consistency and ropiness,

and could be kept for weeks or even months in a cool

room.

0002The home production of fermented milks is now

much less common in Scandinavia, but many types of

commercially manufactured products have the same

attributes as their homemade precursors. Consump-

tion statistics provide ample evidence of the continu-

ing demand for Nordic fermented milks, although the

growing popularity of yogurt has led to some erosion

of this traditional market in recent decades.

0003Interest in Nordic fermented milks has recently

been stimulated by reports of prophylactic and thera-

peutic effects associated with starter flora and its

metabolites, which have been observed in experi-

ments on animals.

General Features

0004Nordic fermented milks constitute a group of prod-

ucts distinctly different from fermented milks made

elsewhere primarily due to their unique physical prop-

erties, characterized by high viscosity and ropiness. In

the cool climate of northern Europe, homemade fer-

mented milks are the result of the spontaneous growth

of mesophilic microflora present in raw milk. Low

FERMENTED MILKS/Products from Northern Europe 2375

temperatures seem to be critical for the domination

of the milk environment by encapsulated strains of

lactococci. Lactobacilli are isolated only rarely from

spontaneously fermented milk in Scandinavia. Molds

and lactose-fermenting yeasts grow well in acidified

milk and are therefore found in some types of Nordic

fermented milks, and influence their properties.

0005 Other traditional fermented products popular in

Scandinavia include cultured buttermilk and cultured

creams, which have a characteristic aroma and flavor,

derived primarily from diacetyl and related volatile

compounds. Also popular are concentrated milks,

made by the removal of whey from the fresh coagulum

or, more recently, using membrane-concentrated milk.

Microorganisms Present

0006 Diverse cultures are used commercially in Scandi-

navia for various types of fermented milk, and have

been derived from traditional products. In many of

these cultures, the bacteria responsible for ropiness

are indispensable. However, the presence of nonropy

organisms is also essential in many cultures to insure

the formation of metabolites which impart typical

organoleptic properties to the product.

0007 Overall, the following groups of microorganisms

have been isolated from various types of traditional

Nordic fermented milks:

0008 Mesophilic bacteria: Lactococcus lactis sspp.

cremoris, lactis, and lactis biovar diacetylactis;

Leuconostoc mesenteroides sspp. cremoris and

dextranicum.

0009 Lactobacillus helveticus. It is significant that the

optimum growth temperature of a strain isolated

from the Norwegian and Finnish version of ta

tm-

lk was 10



C lower than that reported for other

strains of this species. Thermophilic L. helveticus

has been isolated from the Icelandic fermented

milk skyr.

0010 Streptococcus thermophilus and Lactobacillus del-

brueckii ssp. bulgaricus, found in skyr.

0011 The yeasts Candida kefir and its teleomorph Kluy-

veromyces marxianus, as well as Torulopsis holmii

and its teleomorph Saccharomyces exiguus, have

been isolated from various types of Nordic fer-

mented milk. The long shelf-life of ropy milk has

been attributed in part to the presence of yeasts,

which are inhibitory against a number of potential

mold contaminants. The inhibitory compound was

inactivated by heat.

0012 The white mold Geotrichum candidum is found in

viili, tette, and other products. G. candidum isol-

ated from a sample of ropy milk and added to a

ropy culture (L. lactis ssp. cremoris), which was

previously not associated with this mold, stimu-

lated the growth of the culture in milk. A cell-free

filtrate of the medium (sterile whey) on which the

mold had grown had a similar effect.

0013Forms of lactococci classified as ‘intermediate’ be-

tween Lactococcus lactis sspp. cremoris and lactis (on

the basis of their physiological characteristics) have

also been found in some ropy milks.

0014The total number of viable bacteria in these prod-

ucts can be very high. For example, up to 10

cfu g

1

have been reported in the Finnish ropy milk called

pitka

piima

. This is a higher concentration of live

bacteria than that in some starter cultures used in

the commercial production of fermented milks.

0015Traditional Nordic fermented milks owe their char-

acteristic high viscosity and ropiness to the vigorous

growth of capsule-forming lactococci, mainly L.

lactis ssp. cremoris. Encapsulated strains of L. lactis

sspp. lactis and Leuconostoc species were also isol-

ated from some products. However, strains of these

species which clearly do not produce capsules are also

found in Nordic fermented milks.

Glycocalyx

0016Terms like ‘slime,’‘capsule,’ and ‘mucoidal (Muc

)

phenotype’ are used interchangeably in the literature,

usually without ascertaining whether the material

in question is capsule-type or slime-type. ‘Capsule’ is

defined as a compact layer of polysaccharide and

‘slime’ as a diffuse layer of polysaccharide, both ex-

terior to the cell wall. As a rule, the capsule of lacto-

cocci is tightly bound to the cell that produced it. In

cases where the physical nature of the material has

not been studied, it would be more appropriate to use

‘glycocalyx,’ a general term which describes the poly-

saccharide-containing material lying outside the cell

wall, although this term is seldom used.

0017Figure 1 shows an encapsulated strain of L. lactis

ssp. cremoris.

0018In some places, the capsular material clearly does

not follow the chain of lactococci. It is possible, how-

ever, that the detachment from the cells occurred

during the preparation of the slide. Slime seems to

be produced in particular abundance during the late

exponential and early stationary phases of growth.

0019Normally, both encapsulated and nonencapsulated

forms of the same species can be isolated from a prod-

uct. As an example, the types and numbers of bacteria

isolated from pitka

piima

are shown in Table 1.

0020L. lactis ssp. cremoris was the organism most often

encountered in this product. It is worth noting that

encapsulated L. lactis subsp. lactis was found only in

samples of ropy milk which did not contain slime-

forming cells of L. lactis subsp. cremoris.

2376 FERMENTED MILKS/Products from Northern Europe

0021 The growth of slime-forming lactococci isolated

from pitka

piima

depended on the presence of nicotinic

acid and riboflavin in the growth medium. It has

also been observed that strains of both L. lactis sspp.

cremoris and lactis found in pitka

piima

were more

likely to grow at 40



C than were the strains of these

subspecies isolated from commercial starter cultures

for fermented milks. The O

demand and CO

produc-

tion of slime-forming cultures of L. lactis sspp. cre-

moris and lactis from pitka

piima

has been observed,

at 19



C, to be two to three times higher than that of

the strains which do not produce slime.

Characteristics of Capsular Material

0022 Studies on ropy fermented milk using scanning elec-

tron microscopy showed that the polysaccharide

slime material remains associated with the cells

which produced it, while also attached to casein

micelle clusters, forming a network responsible for

the ropy consistency of the product. Other milk pro-

teins may also be involved. In addition, proteins of

bacterial origin may be present in slime. However, the

results of studies on slime composition are affected, to

some extent, by the technique used to isolate and

purify the slime.

0023In one study, the slime produced by a strain of

L. lactis ssp. cremoris isolated from a Swedish ropy

milk was found to contain 47% protein, 20% methyl

pentoses, approximately 10% hexose-like sugars, and

almost 3% sialic acid. The composition of a phos-

phorus-containing polysaccharide produced by

L. lactis subsp. cremoris isolated from a sample of

the Finnish fermented milk viili is shown in Table 2.

0024Rhamnose, glucose, and galactose were present in

this phosphopolysaccharide at the molar ratio of

1:1.45:1.75. The purification procedure (preparative

fig0001 Figure 1 Lactococcus lactis ssp. cremoris, strain Va, after 6 h growth. Preparation stained with methylene blue, magnification  1350.

From Forse

n R (1966) Die Langmilch (Pitka

pilma

). Meijeritieteellinen Aikakauskirja 26: 1–76 with permission.

tbl0001 Table 1 Types of bacteria identified in pitka

piima

; the numbers of slime-forming colonies are shown in parentheses

Ropy milkculture Number of characterized

colonies

Leuconostoc spp. L. lactis subsp.

lactis

L. lactis subsp.

lactis

L. lactis subsp.

cremoris

Streptococcus

viridans group

29 (4) 9 2 (2) 18 (2)

16 (5) 3 6 (1) 2 5 (4)

20 (2) 6 3 4 (2) 7

VA 42 (10) 5 (5) 7 (4) 30 (1)

Jo 13 (3) 7 (1) 2 (2) 4

In 17 (4) 2 3 (1) 4 8 (3)

Total 137 (28) (5) (9) (3) (11)

Percentage of

slime-forming colonies

100% 18% 32% 11% 39%

Streptococus viridansH physiological group includes S. thermophilus, but the result reported above does not imply the presence of S. thermophilus in

pitka

piima

From Forse

n R (1966) Die Langmilch (Pitka

piima

). Meijeritieteellinen Aikakauskirja 26: 1–76 with permission.

FERMENTED MILKS/Products from Northern Europe 2377