Cheese product and method of preparing

The present invention firstly relates to a method for preparing a hard or semi-hard cheese product, at least comprising the following steps:

allowing milk to curdle by adding a suitable coagulant, other customary additives optionally also being added, and wherein a mesophilic starter culture is applied,

after curdling, cutting the curd formed and separating off the whey, and

pressing cheeses,

wherein in addition to the starter culture yoghurt comprising live yoghurt bacteria is added to the milk, the method being characterised in that the yoghurt culture comprises Streptococcus thermophilus and Lactobacillus bulgaricus in a weight ratio of mesophilic culture to yoghurt bacteria from 0.30 to 0.02.

Cheese products prepared by the above method have a number of advantageous characteristics, including a smooth texture and a pleasant refreshing tart, sweet, nutty and strong taste. The cross section of the product also has the striking apppearance because of the presence of relatively large holes.

Milk is used primarily to indicate conventional cows milk, but is also used to indicate cows milk treated in any way involving, for example, at least partial removal of the fat or its replacement by other fats and/or oils, for example of vegetable origin.

The invention is not limited to the addition of yoghurt for providing the yoghurt bacteria, but also encompasses a method in which such yoghurt is prepared in situ by addition of suitable microorganisms. Preferably the mesophilic culture/yoghurt bacteria ratio is 0.1 to 0.04.

An example of a mesophilic culture is the so called BOS-culture (available from Nederlands Instituut voor Zuivelonderzoek) used in the examples. Other well known mesophilic cultures are also suitable for the purpose of the invention.

Yoghurt to provide for the yoghurt culture is preferably added in an amount of 5 to 25% by weight, more preferably 8-15% by weight and in particular 10% by weight of the total mass.

It has been found that the quality of the cheese products declined when more than 25% by weight of an acidified milk product was added in the preparation thereof.

Yoghurt usually has a pH value which is between 3.5 and 5 and contains 10⁷ to 10⁹ micro-organisms per gram.

The use of yoghurt in the preparation of cheese products is found appreciably to shorten the time needed for the so-called "acidification". Acidification means allowing a cheese to stand after it has been pressed, in order to allow it to acidify to a suitable pH. The cheese is then salted, usually in a brine bath.

To improve the taste of the cheese products prepared by the method according to the invention the mesophilic culture preferably comprises at least one aroma former. Examples of such aroma formers are Leuconostoc cremoris and Streptococcus diacetylactus.

Advantageously prior to addition to the cheese milk, the yoghurt is increased in pH level to at least 5.2, preferably at least 6 while the range 6.6 to 6.7 is optimal. This pH increase prevents the formation of brittle and very sour curd and subsequent formation of brittle cheese. If the pH is not raised, the end product is found to have a relatively granular, non-elastic "short" texture; however, after ripening this defect diminishes.

In particular the starter culture is added in an amount of 0.1-1.5%, preferably 0.15%-0.55% by weight of the total mass.

From Revue Laitiere Francaise 445, p.56-57 (1985) a method is known for the preparation of cheese from recombined milk. As a starter culture a mixture is used of 50% mesophilic culture (Streptococcus lactis) and 50% thermophilic (yoghurt) culture (Streptococcus thermophilus+Lactobacillus bulgaricus or Streptococcus thermophilus+Lactobacillus helveticus). The mesophilic culture is a culture wherein no aroma forming bacteria are present. In total 2.2% culture is added which means that only 1.1% yoghurt is added. With the method according to the invention a so-called BD culture is used containing two aroma forming species in combination with a yoghurt culture. Although this reference describes a pH correction it concerns a downward correction, contrary to the upward correction according to the present method. Prior to coagulation, pre-acidification of the milk is applied.

From WO-A-82 03971 the use of a combination of normal cheese starter culture and yoghurt culture is known for the preparation of low-fat cheese. According to this method the normal starter culture and the yoghurt culture is used approximately in the same amount. In addition to the normal starter culture and yoghurt culture also Lactobacillus casei is used.

The invention further provides a cheese product of the kind of a hard or semi-hard cheese in the preparation of which yoghurt culture is used, characterised in that the cheese possesses a Gaba/Glu (gamma amino butyric acid/glutamic acid) ratio of at least 0.1, said cheese product being obtainable by the method according to the invention.

The Gaba/Glu ratio relates to the ratio of gamma amino butyric acid to glutamic acid and is preferably at least 0.25. Although Applicant does not wish to limit the present application to any mechanism, tests showed the following. A substantial amount of CO₂ is produced during ripening of the cheese according to the invention by decarboxylation of free amino acids. For instance the decarboxylation of glutamic acid (Glu) yields gamma amino butyric acid (Gaba), in which reaction process CO₂ is formed. Said carbon dioxyde production accounts for the striking appearance of the cheese possessing large holes (eyes).

In particular the cheese product comprises eyes with a total volume of at least 4% (v/v) of the total cheese volume.

It is further preferred to pasteurise the milk before adding the yoghurt. Pasteurisation can be carried out, for example, by holding the milk at 72° C. for 30 s.

The invention will be illustrated below with the aid of examples of methods according to the invention with which four cheese products A, B, C and D were prepared.

The methods were based on a generally known method for the preparation of Gouda 48+ using cows milk. The various process variables and the amounts of the constituents used are shown in Tables 1-3. Overall, the methods comprise the following steps: Firstly, yoghurt was added to pasteurised milk, but in the case of cheese D the mixture of yoghurt and milk was pasteurised after addition of the yoghurt (30 s at 72° C.). If necessary, the pH of the acidified milk product or the mixture of acidified milk product/milk was corrected using a 3% food-grade NaOH solution. The mixture was then allowed to curdle after adding coagulant, and other additives, including calcium chloride, sodium nitrate and starter, the latter in two different amounts, that is to say the customary amount of starter for the Gouda 48+ method and half of this amount. The curd were then processed in accordance with a standard cutting/stirring programme (Gouda 48+ method). After a portion of the whey had been drained off, the curd particles were washed with an amount of water (±10% extra compared with cheese A), the post-heating temperature being 32° C. in accordance with the regular Gouda 48+ method. The final steps were pressing in accordance with the Gouda 48+ method, acidification to pH 5.8, brining and storage for maturing.

A is a reference cheese, which was produced in accordance with the standard Gouda 48+ method without the addition of yoghurt.

B is a cheese which was obtained using 10% by weight of yoghurt and without pH correction prior to curdling and without yoghurt pasteurisation.

C is a cheese which was obtained using 10% by weight of yoghurt and with pH correction to pH 6.65, but without yoghurt pasteurisation.

D is a cheese which was obtained using 10% by weight of yoghurt, pH correction to pH 6.70 and with pasteurisation of the yoghurt/milk mixture.

The process data for the respective cheeses and the analytical data for the cheeses obtained are given in Tables 1-3. All percentages indicated are percentages by weight. Cheese C was found to be of the best quality, both with respect to the taste and with respect to the consistency. This cheese had a refreshing tart, sweet, nutty and strong taste (denoted as "yoghurt cheese taste"), a smooth texture and the striking appearance resulting from the presence of relatively large holes.

The starter culture used in the examples is BOS. This is a culture comprising Streptococcus lactis, Streptococcus cremoris, Leuconostoc cremoris and Streptococcus diacetylactus.

Table 4 shows the results of the quality assessment of the cheeses by a test panel after maturation for 12 weeks. In this table, N is the number of persons in the panel. The persons gave an assessment on a scale of 0 to 5 and the averages of these assessments are shown in the table. Cheese C is obviously the cheese with the best overall quality.

Table 5 shows the results of the quality assessment of cheeses by the same test panel after maturation for 12 weeks. The cheeses were all prepared by the same method as used for the preparation of cheese C although the yoghurt addition to the cheese milk was varied, i.e. 1% (w/w), 5% (w/w), 10% (w/w), 15% (w/w), 20% (w/w) and 25% (w/w). It should be noted that the holes get the appearance of irregular cavities with yoghurt additions of 20% and higher.

Table 6 shows the characteristic qualities of cheese C with varying % BOS addition to cheese milk. From this table it is clear that when yoghurt culture and a mesophilic culture like BOS are used together the characteristic eye formation takes place in the cheese product. Further it appears that 0.35% BOS (w/w) gives the best taste according to an expert panel.

Table 7 gives the results of tests on the gaba/glu ratio of cheese C with time as well as of an ordinary Gouda cheese. It appears that the gaba/glu ratio is high in cheese C, in any case very much higher than in Gouda cheese. The decreasing gaba/glu ratio in cheese C with time shows that decarboxylation of glutamic acid into gamma amino butyric acid, in which reaction process the CO₂ is formed which probably causes the eye-formation, takes place already in the first 15 days.

                                  TABLE 1__________________________________________________________________________PRODUCT DESCRIPTION                                                  1st 2ndConstituent        pH of yoghurt                          Starter   MILK          Whey                                                      Whey    CaCl2   NaNO3 before         conc.  Coagulant                                          fat amount                                                  fat fatCheese    (g) (g) (% yoghurt)              addition                      process                          type                             (%) pH (%)   (%) (l) (%) (%)__________________________________________________________________________A   60  50  --                 BOS                             0.7 4.34                                    0.030 3.35                                              250 0.30                                                      0.15B   60  50  10     3.83        BOS                             0.35                                 4.32                                    0.030 3.35                                              250 0.30                                                      0.15C   60  50  10     6.65        BOS                             0.35                                 4.32                                    0.030 3.36                                              250 0.40                                                      0.15D   60  50  10     6.70    paste-                          BOS                             0.7 4.28                                    0.030 3.36                                              250 0.40                                                      0.15                      urised__________________________________________________________________________

                                  TABLE 2__________________________________________________________________________PROCESS VARIABLES            Wash-                Post-    Acidifi-Curdling    1st Whey            water                heating  cation                              Pickling                                   Cheese weight   time       tapped            added    time                         time time       before                                               after                                                    afterCheese    temp.   (min)       (l)  (l) temp.                     (min)                         (min)                              (h)  °Be                                      pH pressing                                               pressing                                                    pickling__________________________________________________________________________A   29  35  110  110 32   8   40   24   18 4.80                                         6.73  5.80 5.66B   29  13  120  120 29   8   --   24   18 4.80                                         7.21  6.24 6.12C   29  57  120  120 32   8   --   24   18 4.78                                         6.43  5.67 5.61D   29  50  110  110 32   8   --   24   18 4.78                                         7.32  6.08 6.05__________________________________________________________________________

                                  TABLE 3__________________________________________________________________________CHANGE      ANALYTICAL CHEESE DATAIN pH                 Acidi-       Solids Fat in       Salt in    Cheese   Acidi-        fica-    Time                              content                                  Fat                                     solids                                          Protein                                              Salt                                                  waterCheese    milk   fication       Curdling            Pressing                 tion                     Pickling                          (days)                              (%) (%)                                     (%)  (%) (%) (%) pH__________________________________________________________________________A   6.71   6.60       6.59 5.99 5.80                     5.24 15  55.3                                  25.1                                     45.4 24.9                                              1.99                                                  4.5 5.38B   6.72   5.80       5.79 5.10 --  5.06 15  47.2                                  21.4                                     45.3 20.9                                              2.31                                                  4.5 4.98C   6.71   6.60       6.60 5.30 --  5.32 13  52.8                                  22.8                                     43.2 24.8                                              1.97                                                  4.2 5.21D   6.73   6.60       6.57 5.61 --  5.28 13  54.8                                  26.6                                     48.5 23.4                                              2.10                                                  4.6 5.26__________________________________________________________________________                            ANALYTICAL CHEESE DATA                                 Solids Fat in     Salt in                            Time content                                     Fat                                        solids                                            Protein                                                Salt                                                   water                        Cheese                            (weeks)                                 (%) (%)                                        (%) (%) (%)                                                   (%) pH__________________________________________________________________________                        A   8    56.8                                     25.8                                        45.4                                            25.6                                                2.04                                                   4.7 5.19                        B   8    50.8                                     23.0                                        45.3                                            22.5                                                2.55                                                   5.2 5.18                        C   8    55.7                                     24.1                                        43.2                                            26.2                                                2.08                                                   4.7 5.47                        D   8    51.3                                     24.9                                        48.5                                            21.9                                                1.97                                                   4.0 5.37__________________________________________________________________________

              TABLE 4______________________________________ASSESSMENT AFTER 12 WEEKS  Global scoresCheese N      Consistency                   Taste quality                             Taste intensity______________________________________A     10     3.9        3.5       3.6B     10     2.8        2.2       3.9C     10     4.4        3.3       3.3D     10     3.5        2.9       3.4______________________________________

                                  TABLE 5__________________________________________________________________________Expert panel results (12 weeks)% Yoghurt Consistency       Taste quality              Taste intensity                      Eye forma-                            Yoghurt cheese                                    mesoph. culture to(w/w) 5 pt scale       5 pt scale              5 pt scale                      tion1)                            taste   Yoghurt cult. ratio__________________________________________________________________________ 1    2.9   2.5    2.9     -     -       0.417 5    2.9   3.2    2.9     ±  ±    0.08410    3.6   3.5    3.8     +     +       0.04215    2.7   3.0    2.6     +     ±    0.02820    2.8   2.8    3.4     +*    -       0.02125    2.0   2.0    3.0     +*    -       0.015__________________________________________________________________________ 1) Eye formation: - less than 2% (v/v) ± 2 to 6% (v/v) + 6 to 10% (v/v) *Irregular cavities

                                  TABLE 6__________________________________________________________________________   Expert panel results (12 weeks)   Consistency         Taste quality                Taste intensity                        Eye   Yoghurt cheese% BOS (w/w)   5 pt scale         5 pt scale                5 pt scale                        formation1)                              taste__________________________________________________________________________0       3     2.8    3.6     -     -0.35    3.6   3.5    3.8     +     ++0.7     3     2.9    3.5     +     +__________________________________________________________________________ 1) see Table 5

              TABLE 7______________________________________Cheese type     Age (days)                     gaba/glu______________________________________Cheese C         5        0.33Cheese C        15        1.77Cheese C        18        0.86Cheese C        28        0.79Cheese C        56        0.70Gouda           56        0.01______________________________________