Handbook of Food Science and Technology 3

Figure 1.27.
 Structure of butter 

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From Milk to Dairy Products 61 
Fat globule crystallization
Cream storage/aging at low temperature aims to induce the partial 
crystallization of fat, thereby promoting phase inversion. By strict control of 
the thermal cycle, it also adapts the consistency of butter to the seasonal and 
geographical variability in milk fat composition. In practice, there are two 
types of aging: 
– low-temperature aging for winter cream, whereby the cream is 
immediately cooled to 6–7°C allowing the formation of many small fat 
crystals; 
– high-temperature aging for summer cream whereby temperatures are 
adapted to obtain large fat crystals. 
After aging, the solid and liquid fat ratio in cream is relatively stable.
Cream fermentation 
Cream fermentation aims to acidify cream, allowing the development of a 
marked and typical aroma, promote phase inversion by decreasing the surface 
potential of fat globules at low pH, and ensure biological protection against 
microorganisms that can degrade butter. The major disadvantage of cream 
fermentation is that it generates an acidic and aromatic by-product after 
churning (buttermilk), which is difficult to stabilize and process further. This 
was the driving force behind the developments in butter technology and the 
introduction of the NIZO process.
Inoculation of cream with 3–5% lactic acid bacteria is achieved using a 
dosing pump. It can be performed either at the beginning of cream aging 
(before fat globule crystallization), resulting in pH values below 5.0, or after 
fat globule crystallization. Currently, the desired final acidity of butter is 
significantly less than it was in the past. Fermentation is usually carried out 
below 15°C for 10 – 12 hours. When the pH reaches a value close to 5.5–5.8, 
ripening is slowed by cooling the cream to 8°C. Butter produced in such a way 
has a storage pH ranging from 5.2 to 5.6.
Phase inversion
Phase inversion involves transforming ripened cream, an oil-in-water 
emulsion, into butter, a water-in-oil emulsion. Phase inversion is performed by 
churning, or vigorous agitation, at a temperature corresponding to the 
optimum ratio of crystallized and liquid fat (normally 10 – 13°C for churning 

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62 Handbook of Food Science and Technology 3 
winter cream and 7 – 10°C for summer cream). During churning, air bubbles 
are incorporated into the cream. The air bubble interface is first stabilized by 
(non-homogenized) fat globules. When they become insufficient in number to 
cover the newly-created interface, the foam collapses causing a rapid 
convergence of fat globules [VAN 01]. Coalescence of fat globules is 
promoted by the reduction of its surface charge depending on cream acidity 
and the presence of fat crystals deforming the fat globule surface. The release 
of liquid fat contained in the fat globules causes an agglomeration of fat 
crystals, intact fat globules and fat globule fragments in the form of granules. 
When a sufficient amount of liquid fat has been released, the granules are 
converted into butter grains in which droplets of buttermilk and small fat 
globules are dispersed. The emulsion is then rapidly reversed and the 
buttermilk is expelled. After washing and optional salting, the butter is 
kneaded to compact the butter grains and ensure homogenization by evenly 
distributing the aqueous phase and salt.
Conventional churning is carried out batch-wise in a barrel churn rotating 
about a horizontal axis. It is generally filled to 40–50% of its volume with 
ripened cream. Rotation ensures the incorporation of air into the cream and 
phase inversion. The churn has an outlet for releasing butter-cream and wash 
water. Continuous churns, or butter-making machines, operate according to 
the same principle as conventional churns, but without interruption. A butter-
making machine consists of a cooled cylinder containing a rotating beater that 
incorporates air resulting in phase inversion and a tilted kneading cylinder 
containing two counter-rotating augers that compress and release the butter. 
The butter is generally washed and kneaded under vacuum to limit the risk of 
oxidation.
1.3.5.3.
 NIZO butter 
The NIZO (Netherlands Institute for Dairy Research) method is used to 
prepare butter from cream that has not been fermented. Apart from this 
exception, all other processing stages remain the same as for the continuous 
manufacture of butter. Acidifying and flavoring agents (NIZO mixture) are 
added at a rate of approximately 0.8 – 1.25% to sweet butter after kneading. 
The NIZO mixture is prepared under aerobic conditions by vigorously mixing 
around 40% of a lactic acid concentrate (lactic acid content of the concentrate 
close to 18%) obtained by culturing 
Lactobacillus helveticus 
in whey, and 
around 60% of a mesophilic lactic starter (
Lactococcus lactis
, 
Lactococcus 
cremoris
and 
Lactococcus diacetylactis
). Intense oxygenation of the mixture is 

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From Milk to Dairy Products 63 
favorable for diacetyl production, characteristic of the butter aroma. The final 
mixture is very acidic and no longer contains live bacteria. This first injection 
is followed by a second injection of live bacterial culture consisting of 
acidifying strains of 
Lactococcus lactis
and 
Lactococcus cremoris
as well as a 
different aromatic strain of the previous culture, 
Leuconostoc cremoris
. 
Leuconostoc cremoris 
is able to consume excess acetaldehyde, responsible for 
the “yoghurt” taste in the NIZO mixture (Figure 1.28).