Process for manufacturing a fermented milk

Description

The invention relates to a method of producing fermented milk, namely mixed or drinkable fermented milk or fresh cheese, comprising a smoothing step after tank fermentation to obtain a homogeneous and smooth texture.

[0002] The mixed fermented milk is incubated in a tank and the final curd is broken by agitation prior to cooling and packaging. The texture resembles a thick cream and is less firm than solid yogurt (which is incubated and cooled in the final package and has a jelly-like compact structure). Drinking fermented milk is very similar to mixed fermented milk, but its viscosity is much lower.

[0003] The mixing operation after fermentation is a key process in the production of mixed or drinkable fermented milk, such as blended yogurt or drinkable yogurt. This unit operation is usually performed with filters or valves.

[0004] In particular, the method also relates to fermented milk which has undergone a high pressure homogenization step prior to fermentation.

[0005] The first known solution for the post-fermentation mixing operation is the continuous agitation of the fermented mass in the tank during the transfer to the cooling operation. However, standard shaking in a tank leads to a large loss of viscosity.

[0006] The second solution, namely the use of a static filter, was a better alternative to smoothing the product, but the development of a new component, some texture innovations, the complexity of the flow conduits for a large mix of different products and changing the target viscosity require a new, more sensitive system for this operation.

[0007] On the other hand, the production of mixed yoghurt using a static filter is not possible without changing the filter due to clogging during production.

[0008] For complete cleanliness it is necessary to clean the filter manually due to the hygiene risks of the products. It also means that production is interrupted during the cleaning operation.

[0009] Certain processes or devices are disclosed in CA 2167020, WO 93/10665, EP 0499041 and DE 3519854.

[0010] CA 2167020 discloses a method of producing fermented milk comprising, after the fermentation step, a smoothing step performed using a rotor-stator mixer. WO 93/10665 discloses a process for the preparation of a water-in-oil solid emulsion such as butter or margarine. EP 0499041 discloses a method for producing processed cheese.

[0011] DE 3519854 discloses an apparatus for mixing and / or homogenizing a fluid material, especially cream.

[0012] The present invention relates to a method for producing mixed or drinkable fermented milk or fresh cheese comprising, after the fermentation step, a smoothing step, said smoothing step being performed using a rotor-stator mixer comprising a ring-shaped rotor and a shaped stator. a ring and in which the radial spacing between the stator and rotor rings is between 0.5 mm and 2 mm, preferably 0.5 mm, each rotor and stator ring is provided with radial slots of a predetermined width including adjusting the rotational speed of the rotor to adjust the peripheral speed.

[0013] The stator head may have three rings and the rotor head may have three rings.

The width of the gap may be between 0.3 mm and 2 mm, in particular between 0.5 mm and 1.8 mm

[0015] The rotor may be operated such that the peripheral speed is no greater than 16 m / s for mixed fermented milk, in particular between 3.5 m / s and 16 m / s or between 5.5 m / s and 11.4 m. / s (depending on the flow rate in the tube and the model of the apparatus).

[0016] For mixed fermented milk (e.g. mixed yoghurt) or fresh cheese with a target viscosity between 300 mPas and 3700 mPas, the peripheral speed is between 3.5 m / s and 16 m / s.

[0017] For a flow rate of between 150 l / h and 20,000 l / h, the peripheral speed is preferably between 3.8 m / s and 15.7 m / s.

[0018] For a flow rate of between 20,000 l / h and 60,000 l / h, the peripheral speed is preferably between 5.5 m / s and 11.4 m / s.

For potable fermented milk (e.g. potable yoghurt) with a target viscosity between 30 mPas and 300 mPas, the peripheral speed is between 22 m / s and 30 m / s at a flow rate between 150 l / h and 20,000 l / h, and preferably between 25 and 30 m / s at a flow rate of between 20,000 l / h and 60,000 l / h. With such a low viscosity, these speeds do not cause high shear rates to the product, thus minimizing viscosity loss.

[0020] The fermented milk may be fat free and the method comprises adjusting the peripheral speed.

[0021] The fermented milk may be a medium fat recipe comprising a fat content between 3% and 5% by weight, and the method comprises adjusting the peripheral speed.

[0022] The fermented milk may have a fat-free recipe with added starch between 1.5% and 3% by weight, and the method comprises adjusting the peripheral speed, the slit width being less than 1mm or the slit width being between 0.3mm and 0. , 8 mm when adjusting the peripheral speed to 11 m / s.

[0023] The fermented milk may have a high fat content between 7.5% and 10% by weight.

[0024] The fermented milk may be fresh cheese, and the method comprises adjusting the peripheral speed, the gap width being between 1mm and 1.5mm.

The invention also relates to a smoothing rotor-stator mixer for carrying out the method as defined above comprising a ring-shaped rotor head and a ring-shaped stator, the radial gap between the stator and rotor rings being between 0.5 mm and 2 mm, and preferably it is equal to 0.5 mm, with each rotor and stator ring provided with radial slots of a predetermined width.

The stator may have three rings and the rotor head may have three rings.

[0027] The gap width may be between 0.3 mm and 2 mm, in particular between 0.5 mm and 1.5 mm.

[0028] The rotational speed of the rotor can be adjusted such that the peripheral speed is not more than 16 m / s, in particular between 3.5 m / s and 16 m / s.

[0029] In the accompanying drawing, figure 1 illustrates the smoothing step according to the invention, figures 2a and 2b show the internal structure of the mixer and figures 3a and 3b illustrate the examination of a fat-free recipe with starch.

[0030] It is worth mentioning that in the prior art there have been many different apparatuses for mixing or dispersing the ingredients in the first step of the process (mixing the ingredients).

[0031] The current fields of application of these devices are homogeneous mixing, suspending and dissolving powders, dispersing applications, emulsifying.

[0032] Neither of these devices can be used to smooth the yoghurt after fermentation, since the direct use of such equipment would result in a high or very high loss of viscosity, which would be unacceptable.

[0033] According to the invention it has been found that a rotor-stator device having a ring-shaped stator and a rotor each having radial slots can be adapted to perform a smoothing operation that minimizes loss of texture, i.e. loss of viscosity.

[0034] A device of this type of the prior art always provides high shear rates, on the one hand due to the dimensioning of the stator and rotor, and on the other hand due to their constant rotation frequency (50 Hz or 100 Hz, i.e. 3000 or 6000 rpm) , corresponding to the speed range of 18-25 m / s. This speed range is not suitable for the process of the present invention for products such as mixed or drinkable fermented milk or fresh cheese.

[0035] The method of the invention relates to fermented milk as defined in the Codex Alimentarius Standard for Fermented Milks (CODEX STAN 243-2003) or to fresh cheese. The preferred product is blended or drinkable yogurt (the meaning of the word "yogurt" is the broadest possible meaning - ie, US meaning). The yogurt according to the invention comprises a product containing certain bacterial strains, such as Lactobacillus spp. Paracasei, Bifidobacterium animalis subsp lactis, Lactococcus spp. laciis, Lactobacillus spp. plantarum ... and a product containing vegetable oils such as phytosterols (and sterol esters) or PUFAs.

[0036] According to the invention, cheese is an unripened semi-solid product in which the whey protein / casein ratio does not exceed that in milk, obtained by:

(a) total or partial coagulation of the following raw materials: milk, skimmed milk, partially skimmed milk, cream, whey cream or buttermilk, or any combination of these materials, by the action of rennet or other suitable coagulating enzymes, and by partial draining of the resulting whey coagulation; and / or

(b) processing techniques involving the coagulation of milk and / or milk-derived materials which provide a final product with similar physical, chemical and organoleptic characteristics, as defined in a).

[0037] Fresh cheese can be obtained by adding rennet to the milk mass, fermenting and draining by centrifugation to obtain a homogeneous paste that can be smooth according to the present invention.

[0038] The product used in the experiments is a yoghurt-based fermented white mass produced with different fat and protein contents ranging from 0-10% FC fat and 3-5.5% PC protein content (by weight) and 1.5-3% starch content in the case of a recipe containing starch.

[0039] These products have been classified into four different categories:

Fat-free formula: FFF (less than 0.5% FC)

Medium Fat Recipe: MFF (between 3% and 5% FC)

FF with starch and gelatin: FFS formulation (less than 0.5% FC with 1.5 - 3% w / w starch).

High fat recipe: HFC (9.5% FC) for yoghurt or fresh cheese.

[0040] The respective specifications and ingredients are summarized in Table 1.

Table 1: White mass recipe specifications

<td>White masses</td><td>Fat (%)</td><td>Protein (%)</td><td>Dry weight (%)</td>

<td>Range</td><td> 0-10</td><td> 3-5,5</td><td></td>

<td>FFF</td><td> 0,05</td><td> 4,90</td><td> 13,70</td>

<td>IFF</td><td> 4,00</td><td> 4,40</td><td> 20,85</td>

<td>FFS</td><td> 0,07</td><td> 4,02</td><td> 10,97</td>

<td>HFC</td><td> 9,6</td><td> 4,35</td><td></td>

[0041] For an FFS formulation, the test compositions contain 2.2% starch and 0.2% gelatin by weight.

[0042] In addition, experiments were carried out with the white matter used to produce fresh cheeses with a fat content between 3.4 and 7.1% and a protein content between 4.9 and 5.4%.

[0043] Figure 1 illustrates the smoothing step according to the invention. Pump 2 is located downstream of the fermentation tank 1. An in-line mixer 10 is placed downstream of the pump. The product is recovered in the tank 20 at the outlet of the in-line mixer 10.

[0044] According to the experimental design, the fermented product is pumped and then made smooth in pump 2 at about 38-39 ° C (depending on the culture) with a target pH of 4.65.

[0045] Samples are taken from the product at 38-39 ° C after the smoothing operation. All the different products are kept at the fermentation temperature until the end of the batch experiments. Then the fermented milk is packed and cooled to 10 ° C in a cooling chamber.

[0046] The samples are stored at 10 ° C prior to analysis.

Figure 2a shows the internal structure of the stator head of the mixer 10 and Figure 2b shows the rotor-stator head assembly of the mixer 10. The stator head 3 consists of three rings 4, each of which is provided with radial slots 5. The rotor head 6 consists of of three rings 7, each of which is provided with radial slots 8. The radial slots 5 and 8 have the width Ws, and the gap in the rotor-stator between the stator rings 4 and the rotor rings 7 is marked as G.

[0048] Figures 3a and 3b illustrate the effect of peripheral velocity (V) on the viscosity of the FFS formulation in DI for an annular gap width of 1.5 mm (a) and 0.5 mm (b) respectively.

The central curve of Fig. 3a shows the effect of the peripheral speed on the viscosity in D1 for a low radial speed (low flow rate Q = 3010 kg / h and large gap width = 1.5 mm): increasing the peripheral speed causes a loss of viscosity.

The middle curve of Fig. 3b shows the effect of the peripheral speed on the viscosity in D1 for a high radial velocity (high flow rate Q = 5000 kg / h and small gap width of 0.5 mm): an increase in the peripheral speed allows the degree of texture to be increased up to 11 m / s (maximum in 2108 at 11 m / s).

In order to obtain the same viscosity values ​​with different parameters of the flow rate (Q) and the width of the annular gap (W), it is necessary to adjust the peripheral speed.

[0052] The residence time in the mixer 10 is approximately a few seconds. The two main components of the velocity field are the peripheral velocity (flow between the rotor-stator gap) and the radius component (flow along the annular gaps).

[0053] The peripheral speed depends on the speed of rotation of the rotor head. On the other hand, the radial velocity depends both on the flow rate and the geometrical parameters of the rotor-stator structure (gap width).

[0054] The aim of the smoothing operation according to the invention is to obtain a smooth and as far as possible lump-free texture with a defined target viscosity.

[0055] By adapting the geometry and the speed of rotation of the rotorstator, a dynamic smoothing can be obtained ensuring slow mixing of the mixed fermented milk, e.g. yoghurt.

[0056] Adjusting the peripheral speed makes it possible to adjust the viscosity of the product and / or to adjust the viscosity in real time during manufacture.

[0057] The fermented milk of the invention may be subjected to a mixing step (very slow mixing) in the fermentation tank sufficient to avoid formation of a compact jelly-like structure, such as traditional solid yoghurt. Thus, it may be considered that the process of the invention comprises double agitation (very slow agitation in the tank, slow agitation or downstream smoothing).

[0058] In contrast, the prior art filters have neither very wide possibilities nor are they suitable for white masses with a high degree of texture and lead to a fast clogging of the filter and the fermented milk obtained still contains lumps. Smoothing with a disc filter is not suitable for a smooth product. With such filters it would be disadvantageous to enrich the milk with concentrated protein and / or cream powder. Conventional mixing in the tank also leads to a high loss of viscosity.

[0059] Obtaining new textures or applying new components with the use of known devices and obtaining a high-quality product under realistic conditions is not technically and economically possible.

EXPERIMENTAL DATA:

Factors and levels

[0060] The mobile apparatus comprises only one rotor-stator generator with 3 rings and a fixed gap between the rotor and stator rings of 0.5 mm. These parameters (1 generator, 3-ring stator and 3-ring rotor) were optimized in the first part of the study

[0061] In the second part, two different models of apparatus (z66 and z 120) are used to determine the size of the apparatus depending on the flow rate (first important factor).

[0062] Three factors are crucial: the flow rate (Q), the peripheral speed (V) which depends on the rotational speed of the rotor head and the width of the annular gap (Ws) to obtain a high quality product, i.e. a product with a high degree of texture, smooth and without lumps.

Measurement

[0063] Dynamic viscosity measurements were performed using a Rheolab MCI rheometer (Physica) on day 1 (DI) and day 15 (DI5). The experiments were performed at 10 ° C. The shear rate used was 64 s'¹. Data was recorded in 10s.

The smoothing operation in the rotor-stator system is a double-mixing process with two major velocity field components: the peripheral velocity (flow between the rotor-stator gap) and the radius component (flow in the annular gaps).

[0065] The best results in terms of product quality are obtained at low rotational speed (corresponding to a peripheral speed of up to 16 m / s) in all cases of high viscosity (&gt; 300 mPas), e.g. mixed fermented milk or fresh cheese.

[0066] Each product requires a different speed value, and the quality (viscosity) responses vary from product to product.

[0067] The results of smoothing five different white masses with the same rotor-stator mixing device show that:

D FORMULA FF

[0068] The peripheral speed is the parameter with the greatest influence. Its relative contribution to the response in terms of viscosity is so important that all other factors are negligible.

[0069] In order to obtain products with a high degree of texture, the circumferential speed must be adapted to the flow rate.

[0070] Under these conditions, to achieve the target viscosity of 1100 mPas, the peripheral speed must be less than 12 m / s.

[0071] The width of the annular gap is the second most important factor. It has a positive effect on viscosity. The optimum is obtained at 1 mm due to the enhanced effect.

[0072] The flow rate has little effect on the viscosity, but the determination of the model dependent on it is also very important.

2) RECIPE OF MF

[0073] The peripheral speed is a parameter that must always be adjusted first in order to obtain a highly textured fermented milk with the greatest possible creaminess and cosmetic perception. With the FF (fat free) formulation, the peripheral speed has a negative effect on the texture.

[0074] Moreover, there is a great relationship between the flow rate and the width of the annular gap. The width of the annular gap is more important when the flow rate is high. Finally, in order to obtain high viscosity products in Dl, the gap width should be the largest at high flow rates.

[0075] The flow rate has little effect on the reactions in terms of viscosity compared to the other factors.

[0076] The pattern (depending on the flow rate) and the gap width were established to minimize radial shear which would have a negative effect on viscosity. Once the apparatus has been defined, the final product viscosity depends on the peripheral speed.

3) FFS RECIPE

[0077] All the factors influence the responses with respect to the viscosity in D1, i.e. flow rate, peripheral velocity, gap width, their interactions and potentiated effects. The optimal viscosity response depends on the ratio of the two major velocity components characterizing the fluid flow (peripheral and radial velocity), hence the corresponding shear rate components and the associated residence times of the fluid particles.

[0078] As the flow rate increases and / or the gap width decreases, the corresponding shear rates increase and thus the viscosity decreases, all other factors remaining the same.

[0079] The peripheral speed has a negative effect on the texture properties when its level is higher than that of the radial speed.

[0080] At a low radial speed (Figure 3a), i.e. a low flow rate and a large gap width, an increase in the peripheral speed makes it possible to reduce the texture degree of the mixed fermented milk (viscosity reduction).

[0081] On the other hand, in the case of high radial speed (Figure 3b), increasing the peripheral speed makes it possible to increase the texture degree (increase in viscosity) of the mixed fermented milk to V = 11 m / s.

4) HFC RECIPE or FRESH cheese RECIPE

[0082] For a dynamic system, like a static system, the fat and protein content has a positive effect on the texture of the product, protein being the most important factor in texture improvement.

[0083] Depending on the static or dynamic smoothing treatment, the overall behavior of any recipe depends on its microstructure, i.e. the cohesiveness of the protein network.

The flow in an in-line rotor-stator mixing device depends mainly on the initial viscosity of the white mass as well as on the microstructure of the white mass.

[0084] As shown in Table 2 below, a surprising texture improvement can be obtained by increasing the speed of the rotor head for some recipes (see also Figs. 3a and 3b).

Table 2: Effect of increasing the rotor speed on the texture of the fermented milk

<td>Fat (%)</td><td>Protein (%);</td><td>Rotational speed (rpm);</td><td>VISCOSITY in Dl (MPas)</td>

<td> 9,57</td><td> 4,35</td><td> 2142</td><td> 1745</td>

<td></td><td></td><td> 4182</td><td> 3713</td>

<td> 0,09</td><td> 3,19</td><td> 2142</td><td> 485</td>

<td></td><td></td><td> 2730</td><td> 712</td>

<td> 6,73</td><td> 5,4</td><td> 2142</td><td> 2790</td>

<td></td><td></td><td> 4017</td><td> 2903</td>

<td> 4,83</td><td> 4,32</td><td> 2142</td><td> 834</td>

<td></td><td></td><td> 3858</td><td> 1091</td>

<td> 2,34</td><td> 5,42</td><td> 2142</td><td> 1321</td>

<td></td><td></td><td> 4097</td><td> 534</td>

<td> 7,43</td><td> 3,06</td><td> 2142</td><td> 1566</td>

<td></td><td></td><td> 3011</td><td> 980</td>

<td></td><td></td><td> 4507</td><td> 604</td>

[0085] For both a product with a low degree of texture (i.e. fat &lt;5.2% and protein &lt;3.7%) and high degree of texture (i.e. fat&gt; 4.8% and protein&gt; 5.2%), the viscosity in Dl obtained using an in-line rotor-stator mixing device is higher than that obtained using a prior art disc filter. With this fermented milk recipe, dynamic smoothing is less detrimental to texture.

[0086] From these results it can be concluded that the fluid flow to the rotor-stator head depends largely on the initial product viscosity. In the case of a low viscosity fluid (FF formulation), the flow would mainly take place at an interval in the rotor. As a result, the peripheral speed and thus also the corresponding shear rate components have a great influence on the texture of the final product. The imbalance between the flow in the rotor-stator gap and the width of the annular gap is more important because the peripheral speed (i.e. the rotational speed of the rotor head) is large compared to the radial velocity (i.e. flow rate). Moreover, this imbalance allows the product to smooth well and remove lumps. This means that there is a medium shear rate threshold to optimize the appearance of the product (smoothness, number of lumps).

[0087] The higher the viscosity of the fluid, the more the laminar flow of the fluid leads to a reduction in the imbalance between the two flows. The "sensitivity of the product" to radial velocity (ie flow rate) will be more important. Consequently, the factors influencing the loss of texture are the flow rate and the gap width (FFS formulation).

[0088] The new smoothing technology is a suitable solution to obtain smooth products irrespective of the fat and protein content and possibly remove lumps resulting in them being perceived as smoother and creamier.

[0089] The built-in rotor-stator mixing device is an apparatus with a very wide potential to improve the texture of the product compared to the static filter by adjusting the rotational speed of the rotor, with other parameters on the rope being fixed (model of the device depending on the flow rate and the width of the slot).

[0090] It is possible to adjust the viscosity of the mass of the fermented milk or yoghurt mass by the rotor-stator system in an easy way by setting a specific peripheral speed, which is obtained by adjusting the rotation speed of the mixer.

[0091] The dimensions of the apparatus are dependent, as outlined above, on the product and on the target viscosity, which generally means a small decrease in viscosity.

[0092] For mixed fermented milk, e.g. mixed yoghurt, or fresh cheese, low rotational speeds (less than 16 m / s) are used.

[0093] For drinking fermented milk, e.g. drinking yoghurt, a high rotational speed (greater than 22 m / s) is used.