Principles of Cheese Technology 239propagate culture to prepare their own bulk
starter.
To prepare bulk starter for inoculation, the
concentrate is transferred to a medium con-
sisting of heat - treated milk, reconstituted
NFDM, or a special whey - based phage -
resistant phosphate medium in a bulk starter
tank and allowed to grow under optimum
conditions. It is then cooled and used at 0.5%
to 1% inoculation level. Refi nements in
starter technology have led to production of
single - strain starter concentrates (direct - to -
vat set/inoculation), which require no sub -
culturing, bulk setting, or activation. Their
use requires simple dilution with pasteurized
milk to furnish adequate active cells to initi-
ate acid development in the cheese vat.
Having a working relationship with the
culture supplier helps to optimize their use
and prevent phage attack, which could slow
acid production or even kill the culture,
leading to huge losses in a cheese plant.
Culture suppliers have information on phage
typing and methods to avoid phage attack by
culture rotation.
The quantity of the starter is important for
the rate of acid development, moisture reten-
tion, fl avor, and texture of cheese. Higher
rates of inoculation may lead to undesirable
fast acid development. It is advisable to
follow the recommendation of the culture
supplier. The temperature of setting milk and
cooking conditions refl ect the optimum
growth temperature and heat ruggedness of
the culture involved.
Production of many cheeses depends on
Lactococcus lactis subspecies lactis and
cremoris for acidity development. These cul-
tures belong to the mesophilic group. Their
acid production is optimum at 30 ° C to 35 ° C
(86 ° F to 95 ° F). However, acid production
essentially stops at temperatures below 20 ° C
(68 ° F) and above 39 ° C (102 ° F). The cremo-
ris sub - specie is generally regarded as the
best for optimum cheese fl avor. The sub -
specie lactis , however, is a better acid devel-
oper. Therefore, the two are often blended inPure, Defi ned Single - strain Starters
Pure, defi ned single - strain starters are
selected from mixed strains for specifi c
characteristics such as phage resistance or
optimum proteolytic profi le. Advancement
in starter production technology has resulted
in single - strain starter concentrates which,
by culture rotation techniques coupled with
plant sanitation, have dominated their use
in larger cheese plants. Defi ned single -
strain cultures have the advantage of unifor-
mity of acid production and fl avor profi le
of cheese. They must be rotated to avoid
phage infection.
Mixed Defi ned Strain
Mixed defi ned strain cultures are blends of
single strain cultures. They must be rotated
to control phage attack. They relatively yield
uniformity of acid production and fl avor
profi le.
Multi - strain Starters
Multi - strain starters are non - specifi c, unde-
fi ned mixtures. Their advantage over single -
strain starters is that acid development is
likely to continue even in the presence of a
phage that is capable of attacking only a
single strain. However, it is known that ulti-
mately a single strain may dominate at the
expense of others. Mixed mesophilic cultures
are still used in the cheese industry, but nor-
mally the thermophilic cultures are mixed
single - strain types. The disadvantages of
mixed cultures are a wide variation in the rate
of acid development as well non - uniformity
of cheese fl avor from vat to vat.
Various starters are available from com-
mercial culture suppliers. Concentrated cul-
tures are available in liquid, frozen, or
freeze - dried forms. Frozen cultures require
expensive sub - zero transportation and
storage. Freeze - dried culture concentrates are
cheaper to transport and store. Some plants