Preparation of evaporated milk

Evaporated milk is prepared by separating a standardized milk into a first flux and a second flux, homogenizing the first flux, mixing the homogenized first flux with the unhomogenized second flux, heat-treating the mixture, evaporatively concentrating the heat-treated mixture, homogenizing the concentrate and then sterilizing the homogenized concentrate.

BACKGROUND OF THE INVENTION 
This invention relates to production of an evaporated milk product 
containing fats. 
Evaporated milk or cream is prepared from whole milk or cream by partial 
removal of the water which it contains. The effect of concentration is to 
bring the fat globules together which can produce a raising of the fats 
during storage. Finally, since evaporated milk is intended for prolonged 
storage, it has to be sterilized. 
When sterilization is carried out by a thermal preserving treatment after 
packing, for example in cans, there is an increased risk of 
destabilization of the liquid phase by heat due to the disturbance of the 
caseinate/calcium phosphate system after concentration. In storage, the 
milk thus treated can thicken and then gel. A standard method of 
overcoming this particular disadvantage is to add stabilizing salts such 
as, for example, disodium phosphate or trisodium citrate. However, these 
additives are being increasingly opposed by food legislation. 
An alternative is the aseptic packing of evaporated milk which has been 
sterilized in-line, for example by the ultra-high temperature or high 
temperature/short time method. U.S. Pat. No. 2,886,450, for example, 
describes a process for the production of evaporated milk sterilized by 
the high temperature/short time method, in which the stability of the 
product in storage is improved by subjecting it to heat treatment and 
homogenization. However, this method does not prevent gel formation in the 
event of prolonged storage. 
SUMMARY OF THE INVENTION 
The problem addressed by the present invention was to provide a process for 
the production of a storable evaporated milk product resistant to the 
acidity of coffee in which the stabilizing salts are reduced or even 
eliminated. 
Accordingly, the present invention relates to a process for the production 
of a storable evaporated milk product containing fats, in which a milk 
standardized to have a ratio by weight of fats to non-fat dry matter of 
0.2:1 to 1.2:1 is heat-treated and then concentrated to a dry matter 
content of 20 to 40% by weight, after which the concentrate is sterilized 
before or after homogenization. 
According to the invention, the problem stated above is surprisingly solved 
by the fact that the milk product is separated into a first flux and a 
second flux, the first flux is homogenized, the first homogenized flux is 
mixed with the second non-homogenized flux, the mixture is heat-treated 
before concentration and the concentrate is homogenized before 
sterilization. 
The first flux is separated from the milk containing fats so that the first 
flux is in an amount of from 25% to 75% by weight of an amount of the 
first and second fluxes, and may be approximately 50% or from 5% to 99% by 
weight of an amount of the first and second fluxes. 
DETAILED DESCRIPTION OF THE INVENTION 
To carry out the process, whole milk is standardized, i.e., the respective 
quantities by way of fats and non-fat solids are adjusted to the desired 
values by addition as required of, for example, skimmed milk, cream or 
butter oil (anhydrous lactic fat). 
In one embodiment of the process, the standardized milk product is 
preheated to 50.degree. to 100.degree. C. and is then separated into two 
fluxes simply by adjusting the entry rate to a value above the exit rate 
from the homogenizer. This gives a first main flux, which is homogenized, 
and a second subsidiary flux which bypasses the homogenizer. 
Homogenization of the main flux preferably takes place under intensive 
conditions. 
The object of homogenization is to increase the surface area of the fat 
globules and better bind the proteins and thus to compensate for the 
relative deficiency of membranel lipids. "Intensive homogenization", is 
intended to mean that the product is treated by one or more passes through 
a single-stage or multiple-stage homogenizer under pressures ranging from 
150 to 500 bar and preferably, by one or two passes in two stages under a 
pressure of 200 to 300 bar for the first stage and then under a pressure 
of approximately 50 bar for the second stage. It is possible in this way 
to obtain a reduction in, and uniform distribution of, the size of the fat 
globules in the flux of homogenized product. 
Unexpectedly, homogenization of only part of the product to be treated 
before concentration is sufficient to produce a substantial increase in 
the stability of the concentrated product. The necessary homogenization 
pressure of 150 to 350 bar is of course also involved in the desired 
increase in stability. The higher the percentage by weight of homogenized 
product relative to the treated product as a whole and the higher the 
homogenization pressure, the more resistant the concentrate will be to 
coagulation during the sterilization phase and hence, the less need there 
will be to add a stabilizing salt, of which the function is precisely to 
avoid such coagulation. 
After homogenization, the main flux is preferably subjected to a holding 
phase, for example of up to 5 minutes at the homogenization temperature. 
The two fluxes are then mixed and preheated. 
They are then heat-treated to stabilize the bonds between the proteins so 
that they remain intact after concentration. This heat treatment may be 
carried out by direct or indirect heating in any standard apparatus which 
enables the liquid to be kept at 80.degree. to 150.degree. C. for 1 to 
1,200 s. The upper temperature limit naturally corresponds to the lower 
time limit. It is thus possible, for example, to combine a plate-type heat 
exchanger with a holding tube and a controlled back-pressure valve, two 
plate-type heat exchangers connected by a holding tube or even a 
plate-type heat exchanger associated with a controlled back-pressure valve 
and a thermostatically controlled holding tank. 
After this heat treatment, the liquid is concentrated by evaporation with 
expansion to a dry matter content of 20 to 40% and preferably 24 to 35% by 
weight in a single-effect or preferably multiple-effect falling-film 
evaporator. 
After concentration, the liquid is homogenized, preferably by a single pass 
through a two-stage homogenizer under a pressure of 75 to 300 bar for the 
first stage and approximately 30 bar for the second stage. The object of 
this homogenization is to break up the clusters of fat globules formed 
during the concentration step and to reduce the size of these fat 
globules. 
After homogenization, the homogenized concentrate may be directly 
heat-treated or temporarily stored. In the first case, the dry matter 
content of the concentrate is adjusted where necessary to the value 
desired for the end product, for example 24 to 33% by weight, by addition 
of water. In the second case, the concentrate is cooled to 
1.degree.-10.degree. C. and preferably to 4.degree.-8.degree. C. and, 
after adjustment of its dry matter content as described above, is left 
standing for 1 to 24 h. The concentrate may also be directly subjected to 
the second heat treatment without temporary storage. 
The second heat treatment may be carried out in the same way as the first 
heat treatment, i.e., by direct or indirect heating at 50.degree. to 
150.degree. C., for example by injection of steam and, after a holding 
time of 1 to 600 s, by expansion in a vessel which results in cooling to 
50.degree. to 100.degree. C. During this second heat treatment, the bound 
proteins are stabilized by partial denaturing. The bonds thus strengthened 
are strong enough to ensure that the proteins are no longer able to 
coagulate during subsequent sterilization. 
Homogenization is then carried out under similar conditions to the 
above-described homogenization and with the same objective, namely to 
break up the clusters of fat globules formed. The homogenizate is then 
cooled to 0.degree.-20.degree. C. and preferably to 4.degree.-8.degree. C. 
and its dry matter content is optionally adjusted to the value desired for 
the end product by addition of water. 
Finally, the milk product is sterilized, if necessary after temporary 
storage. In a first embodiment of this sterilization, the milk product is 
packed in containers, for example in metal cans, glass bottles or 
heat-resistant plastic bottles which are hermetically sealed, after which 
the containers are treated in a sterilizer for 30 s to 60 mins. at 
95.degree. to 135.degree. C., the upper temperature limit corresponding to 
the lower time limit, either in a single stage or by progressive increases 
in temperature. 
In one variant of sterilization, in-line sterilization is followed by 
aseptic packing. To this end, the concentrate is preheated to 
50.degree.-90.degree. C. and subjected to in-line sterilization by 
indirect or direct heating, for example for 2 s to 1 h at 105.degree. to 
150.degree. C., the upper temperature limit corresponding to the lower 
time limit, and preferably by high-temperature/short time or ultra-high 
temperature treatment. The milk product is then cooled to 
50.degree.-90.degree. C., if necessary by expansion, and homogenized in 
one or more passes and in one or two stages at 50 to 300 bar, preferably 
in one pass first under a pressure of 200 to 250 bar in the first stage 
and then under a pressure of approx. 50 bar in the second stage. Finally, 
the milk product is cooled to 4.degree.-30.degree. C. and preferably to 
around 20.degree. C. and is then packed, for example in metal cans or 
cartons. The operations following sterilization naturally take place under 
aseptic conditions. 
In one non-preferred variant of the process, the homogenized flux may be 
added to the subsidiary flux after concentration and homogenization 
thereof and the mixture subsequently sterilized. In a preferred form of 
this variant, the homogenized flux may be heat-treated before mixing with 
the flux which has not been homogenized before concentration. 
The milk product prepared in accordance with the invention without 
stabilizing salts, or with a reduced content of these salts, is stable in 
storage in the same way as conventional products containing, for example, 
approximately 0.14% by weight stabilizing salts. In addition, it can be 
sterilized with very little, if any, of these particular additives which, 
hitherto, have been considered to be indispensable for avoiding gel 
formation and/or coagulation during sterilization. In addition, it is 
sufficiently resistant to the acidity of a hot water-containing coffee 
extract and does not to produce any flocculation when added to the extract 
stabilizing salt in an amount of from 0.02 to 0.2% may be added before 
concentration. 
Another very interesting effect of the process according to the invention, 
in its preferred embodiment, is that it provides for a substantial 
increase in the homogenization pressure during homogenization of the 
concentrate which would normally result in coagulation during subsequent 
sterilization. In addition, the fact that only part of the starting 
material is treated by homogenization, without affecting the storage 
stability of the product as a whole, affords a significant economic 
advantage.

EXAMPLES 
The invention is illustrated by the following Examples in which parts and 
percentages are by weight unless otherwise indicated. 
EXAMPLES 1 to 9 
A whole milk is standardized by addition of cream to give a starting 
material containing 8% fats and 17% non-fat milk solids. This starting 
material is preheated for 30 s to 80.degree. C. in a plate-type heat 
exchanger and is then passed through a two-stage homogenizer in which the 
throughput is controlled so that a flux representing the percentage 
indicated below of the inflowing flux is treated, the rest being diverted, 
i.e., not undergoing homogenization. The pressures indicated below prevail 
in the first stage and in the second stage, if any. The homogenized and 
non-homogenized fluxes are then mixed and the mixture obtained is heated 
for 72 s to 120.degree. C. in a plate-type heat exchanger. 
In a variant of Example 1, preheating to 120.degree. C. may be followed by 
cooling to 96.degree. C. for 8 minutes in a tank (Example 4). The mixture 
is then directed to a falling-film evaporator in which it is concentrated 
to 25% dry matter by expansion "in vacuo". The concentrate is preheated to 
70.degree. C. and is then treated in a two-stage homogenizer under the 
pressures shown below. The homogenized concentrate is cooled to 5.degree. 
C. and poured into glass bottles which are hermetically sealed and then 
sterilized for 15 minutes at 117.degree. C. in a continuous rotary 
sterilizer. In a variant of Example 1, the bottles may be treated for 8 
mins. at 120.degree. C. (Example 5). 
For comparison (Comparison Examples 1, 2, 3 and 4), the same treatment is 
carried out with homogenization of all the starting material. 
The results obtained by addition of 0.14% disodium hydrogen phosphate, but 
without homogenization of the starting material (Comparison Example 5), 
are also compared. 
The stability of an evaporated milk in storage is evaluated by examination 
of the viscosity (N.s.) of the sterilized product, which serves as 
criterion because thickening is, so to speak, the precursor of 
coagulation. The higher the viscosity after sterilization, the less stable 
the product was before sterilization, and even lower is its stability in 
storage. The end product is considered to have coagulated when the 
viscosity reaches the upper limit of approximately 23 to 25 N.s. 
The results of viscosity measurement and the conditions of the process are 
set out in Table I below. 
TABLE I 
______________________________________ 
Homogenization 
Homogeniza- 
pressure of the 
tion of the 
Homogen- starting material 
concen- Viscos- 
Exam- ized flux in one or two 
trate in two 
ity 
ple % stages (bar) stages (bar) 
(N.s.) 
______________________________________ 
1 75 250 + 50 170 + 30 16 
2 50 250 + 50 170 + 30 17 
3 25 250 + 50 170 + 30 20 
4 75 250 + 50 170 + 30 16 
5 75 250 + 50 170 + 30 16 
Compar- 
100 250 + 50 170 + 30 15 
ison 1 
Compar- 
100 170 + 30 170 + 30 22 
ison 2 
6 75 300 85 + 15 16 
7 50 300 85 + 15 16.5 
8 25 300 85 + 15 17.5 
Compar- 
100 300 85 + 15 16 
ison 3 
9 50 300 170 + 30 17.5 
Compar- 
100 300 170 + 30 15.5 
ison 4 
Compar- 
-- -- 170 + 30 
17.5 
ison 5 
______________________________________ 
The above results show the unexpected effect of partial homogenization of 
the starting material before concentration and the effect of the total 
homogenization pressure for the same treated flux (Examples 2, 3 and 4) on 
the stabilization of evaporated milk by comparison with total 
homogenization (Comparison Examples 1, 2, 3 and 4). 
In addition, the results obtained by partial homogenization of the starting 
material are comparable with those obtained by addition of a stabilizer, 
but without homogenization of the starting material before concentration 
(Examples 1-5, 6-8 and 9 compared with Comparison Example 5). 
EXAMPLES 10-15 
These Examples document the relationship which exists between the viscosity 
of the evaporated milk after sterilization and the quantity of stabilizing 
salt (Na.sub.2 HPO.sub.4) added in the process according to the invention, 
on the one hand, and in a conventional process, on the other hand 
(Comparison Example 6). 
The results relating to the viscosity of the evaporated milk as a function 
of the parameters of the process are set out in Table II below: 
TABLE II 
______________________________________ 
Homogenization 
Homogen- pressure of the 
ized starting material 
Na.sub.2 HPO.sub.4 
Exam- flux in one or two 
added Viscosity 
ple (%) stages (bar) (%) (N.s.) 
______________________________________ 
10 50 250 + 50 0.06 15.5 
11 25 250 + 50 0.1 16.5 
12 25 170 + 30 0.12 16.5 
13 50 300 0.06 16 
14 75 300 0.08 15 
15 50 250 + 50 + 0.02 15 
5 mins. holding 
time at 80.degree. C. 
Compar- 
-- -- 0.12 17 
ison 6 
______________________________________ 
The results set out in Table II above show that the partial homogenization 
of the starting material enables the quantity of stabilizing salt added to 
be considerably reduced for a comparable viscosity of the product after 
sterilization. The viscosity conditions in these Examples and for the 
conventional process are the minimum viscosity conditions corresponding to 
the highest stabilization possible by the addition of stabilizing salt 
because the viscosity decreases, passes through a minimum and then 
increases again when the quantity of stabilizing salt is increased. 
More particularly, it has been found that the higher the percentage of 
homogenized flux, the smaller the quantity of stabilizing salt which 
should be added to reach the corresponding minimum viscosity. 
EXAMPLE 16 
The procedure is as in Example 1 except for sterilization. For 
sterilization, the concentrate is preheated to 80.degree. C. in a 
plate-type heat exchanger, subsequently sterilized at 120.degree. C. in a 
plate-type heat exchanger and then held for 7 minutes at that temperature 
in a holding tube. The concentrate is then expanded in a vessel where its 
temperature falls to 78.degree. C. and is then homogenized in two stages 
at 200 bar and then 50 bar, after which the homogenizate is cooled to 
20.degree. C. in a plate-type heat exchanger and packed in cans which are 
hermetically sealed. Expansion, homogenization, cooling and packing are 
carried out under aseptic conditions. The product has the same stability 
in storage at ambient temperature as an evaporated milk stabilized with 
phosphate salts. 
EXAMPLE 17 
The procedure is as in Example 1 except for sterilization. For 
sterilization, the concentrate is preheated to 75.degree. C. in a 
plate-type heat exchanger, subsequently sterilized at 140.degree. C. by 
direct injection of steam and held at that temperature for 10 s in a tube 
(ultra-high temperature sterilization). After cooling to 73.degree. C. in 
a plate-type heat exchanger, it is homogenized in two stages at 250 bar 
and then 50 bar, after which the homogenizate is cooled to 20.degree. C. 
in a plate-type heat exchanger and packed in cartons which are 
hermetically sealed. All the steps after sterilization are carried out 
under aseptic conditions. The product has the same stability in storage at 
ambient temperature as an evaporated milk stabilized with phosphate salts. 
For comparison, an evaporated milk treated in the same way, but without the 
steps of partial homogenization of the starting material, heat treatment 
of the homogenizate before concentration, heat treatment and 
homogenization of the concentrate described in detail in Example 1, would 
gel rapidly after an ultra-high temperature sterilization treatment. 
In the foregoing description, evaporated milk was stabilized by partial 
homogenization of cow's milk before concentration. Analogous results would 
be obtained by corresponding treatment of milk from other mammals, for 
example cow-buffalo's milk, goat's milk or ewe's milk, without departing 
from the scope of the invention.