394 DAIRY CHEMISTRY AND BIOCHEMISTRY
but the lower its stability. Syneresis is promoted by:
0 cutting the curd finely, e.g. Emmental (fine cut) versus Camembert (large
0 low pH (Figure 10.1Ob);
0 calcium ions;
0 increasing the cooking temperature (Camembert, c. 30°C; Gouda, c. 36°C;
Cheddar, c. 38°C; Emmental or Parmesan, 52-55OC) (Figure 10.1Oa);
0 stirring the curd during cooking;
0 fat retards syneresis, while increasing the protein content (up to a point)
improves it; at high protein concentrations, the gel is too firm and does
not synerese (e.g. UF retentate).
Gels prepared from heated milk synerese poorly (assuming that the milk
does coagulate). Such reduced syneresis properties are desirable for fer-
mented milk products, e.g. yoghurt (milk for which is severly heated, e.g.
90°C x 10min) but are undesirable for cheese.
Good analytical methods for monitoring syneresis are lacking. Principles
that have been exploited include: dilution of an added marker, e.g. a dye,
which must not adsorb on to or diffuse into the curd particles, measurement
of the electrical conductivity or moisture content of the curd or by
measuring the volume of whey released (probably the most commonly used
method although only one-point values are obtained).
cut);10.2.3 Acidification
Acid production is a key feature in the manufacture of all cheese varieties -
the pH decreases to about 5 (k0.3, depending on variety) within 5-20h, at
a rate depending on the variety (Figure 10.11). Acidification is normally
achieved via the bacterial fermentation of lactose to lactic acid, although an
acidogen, usually gluconic acid-6-lactone, alone or in combination with
acid, may be used in some cases, e.g. Mozzarella.
Traditionally, cheesemakers relied on the indigenous microflora of milk
for lactose fermentation, as is still the case for several minor artisanal
varieties. However, since the indigenous microflora varies, so does the rate
of acidification and hence the quality of the cheese; the indigenous micro-
flora is largely destroyed by pasteurization. ‘Slop-back’ or whey cultures
(starters; the use of whey from today’s cheesemaking as an inoculum for
tomorrow’s milk) have probably been used for a very long time and are still
used commercially, e.g. for such famous cheese as Parmigiano-Reggiano and
Comte. However, selected ‘pure’ cultures have been used for Cheddar and
Dutch-type cheeses for at least 80 years and have become progressively more
refined over the years. Single-strain cultures were introduced in New
Zealand in the 1930s as part of a bacteriophage control programme.
Selected phage-unrelated strains are now widely used for Cheddar cheese;