152
Quality of Indian and Western Table Butters
flavour (out of 100), 25 for body, 15 for salt, 10 for colour and 5 for package
[Parker and Shadvik Jr. 1937]. Even from the customer's point of view, a
good quality butter put in the market is selected from its flavour and appear
ance. It is evident, therefore, that flavour is one of the most sensitive and im
portant factor in determining the quality of butter. As early as 1850 it was
known to butter makers that the flavour of butter could be definitely influenced
by souring — generally called ' ripening ' — of the cream before churning.
In 1884, Storch, a Danish bacteriologist, demonstrated that pure cultures of
lactic acid forming bacteria could be used as an effective souring agent for
pasteurised cream. Various workers have made valuable contributions to
this subject, but the discovery in 1919 by Hammer and Bailey in U. S. A.
and by Bockhout and de Vries [1919] in Holland proved that the desirable
flavours in butter cultures, or ' starter ' as the butter maker calls it, depended
upon at least two different types of bacteria. It was, however, only recently
discovered in Holland by Van Niel, Kluyver and Derx [1929], while studying
propionic acid fermentation processes, that diacetyl (CH 3 —CO—CO—CH 3 )
was responsible for the characteristic aroma of fine butter. They found from
two to four parts per million of diacetyl in fine butter and when these small
amounts were added to a butter neutral in flavour, there was developed a fla
vour and odour unmistakably similar to that of good butter. They, therefore,
concluded that diacetyl is either responsible for aroma of butter or is the princi
pal component of the aromatic ingredients. These workers also found that
bacteria causing fermentation of citrates in milk were responsible for the
production of diacetyl and associated neutral compounds.
Diacetyl, the pungent, penetrating, odouriferous compound is considered
to come from the relatively rapid oxidation of the odourless acetyl-methyl-
carbinol (CH 3 —CHOH—CO—CH 3 ). Michaelian, Farmer and Hammer [1933]
found that butter and butter cultures with satisfactory flavour and aroma con
tained considerable quantities of acetyl-methyl-carbinol plus diacetyl, while
those lacking in flavour and aroma contained small amounts or none. Fur-
thermo e, Michaelian and Hammer [1935] have reported that butter contains
much smaller amounts of acetyl-methyl-carbinol and diacetyl than the cream
from which it was churned (⅓ to 1/30 of the total amount of acetyl-methyl-
carbinol and diacetyl present in cream goes into butter).
The typical lactic acid forming bacteria such as Streptococcus lactis and
Streptococcus ceremoris (Jensen), produce lactic acid with little if any flavour ;
while the citrate forming bacteria such as Streptococcus citrovorous and Strep-
tococcus para citrovorous [Hammer, 1936] are aroma producers, but they only
produce flavour and aroma either when grown in symbiotic relations with the
lactic acid forming bacteria or when milk is first artificially acidified to the
proper hydrogenion concentration.
Very recent observations by Blaisse and Martin [1938] have brought
out a new carrier of true butter aroma, namely, methyl glyoxal. It is a close
chemical relative of diacetyl and can also be produced by the bacteria of milk.