IE84600B1 - Production of ice-cream - Google Patents

Description

Production of Ice-Cream Introduction The present invention relates to a process for making ice-cream.

In the mass production of ice-cream, there are major problems. While ice-cream itself is a relatively simple product to make, when made in relatively large batches, there are certain problems.

Most of these problems relate to the final organoleptic properties of the ice-cream which should have a creamy texture and should be frozen in such a way that large ice crystals are not formed and mixed with the ice-cream. The difference in organoleptic properties between various types of ice-cream is basically quite subtle and very difficult to quantify.

For example, for many reasons, skim milk powder and butter oil, that is to say, anhydrous butter fat are used as an alternative to skimmed milk and full cream respectively. UK Patent Nos. 2,193,873 and 2,076,275 describe the preparation of an ice-cream composition wherein skimmed milk powder and butter or butter fat are used.

In this specification, skimmed milk is generally milk with not more than 0.2% w fat, full fat milk has generally between 3.5% and 4.5% w fat, and cream has generally between 25% and 50% w fat. organoleptic properties of the ice-cream are acceptable, there are other problems in In addition to the necessity to ensure that the that the use of skim milk powder requires the reconstitution of the powder by dissolving in water, and the use of butter oil causes considerable handling and storage problems.

However, there would not, on the face of it, appear to be any particular differences between the use of, for example, a skimmed milk or, more correctly, butter milk, that is to say, the skimmed milk before it has "soured", and reconstituted skimmed milk from milk powder.

In an effort to ensure that, after manufacture, the ice-cream can be formed so as not to provide relatively large crystals, it is known to blast freeze the ice-cream as quickly as possible to a very low temperature such as of the order of -20°C to -25°C. aitinni Unfortunately, in many commercially provided freezers, the manner in which the ice- cream manufacturer freezes the resultant ice-cream is such as not to freeze the ice- cream quick enough and while many portions of the ice-cream are frozen quickly, very often some of the ice-cream is not frozen quickly enough and thus unacceptably large ice crystals are formed within the product, reducing the overall creaminess of the product.

US Patent No. 5,112,626 describes the preparation of an ice-cream product without the addition of stabilizing gums, comprising a source of milk protein obtainable from skim milk, whole milk, buttermilk or milk powder. The stability and creaminess of the ice- cream product are improved by the addition of partially hydrolyzed starch and egg.

Further, the conventional manufacturing technique, with the use of butter oil and reconstituted skimmed milk, require a longer time to carry out, than is desirable.

Statements of Invention According to the invention there is provided a process for making ice-cream comprising the steps of:- preparing a base starter liquid of cream, milk and water and at least 30% weight by weight of skimmed milk; mixing the base liquid and solid ingredients including sugar, stabilisers and emulsifiers, while heating the liquid to between 45°C and 60°C for between 10 and minutes; pasteurising the liquid at greater than 82°C for between 13 and 17 seconds; cooling the pasteurised liquid to less than 7°C within two hours; retaining the liquid to condition the liquid for between 4 and 48 hours; freezing the mixture in an initial freezing process to between -3°C and -7°C, while adding air at a pressure of between 3 and 4 bar after delivering the air through a bacterial filter; filling the ice-cream, so produced, into individual containers of a size not greater than 4 litres; placing the individual containers in a spaced—apart relationship in a freezer to ensure adequate direct exposure of the exterior of each container; and freezing the individual containers to between -20°C and -25°C within a period not exceeding three and a half hours. in one embodiment of the invention the amount of skimmed milk exceeds 50% by weight of the base starter liquid.

Preferably the liquid is conditioned for between 12 and 18 hours.

Further preferably the initial freezing is within the range -3.5°C to -4°C. in a further embodiment of the invention the mixing and pasteurising of the base liquid and solids comprises:- mixing in a mixing tank; delivering from the mixing tank to a heat exchanger to heat the mixture; then homogenising the product in a homogeniser; delivering the homogenised liquid to the heat exchanger to pasteurise the liquid; then cooling the liquid in the heat exchanger.

Preferably the skimmed milk has a fat content of between 0.10% and 0.15% w fat.

Skim milk powder may also be added during the process.

The advantages of the present invention can be summarised that by the use of a skimmed milk rather than reconstituted skimmed milk, i.e. milk powder and water mixed together, there are surprisingly better whipping and mixing properties which produces a frothier and lighter ice-cream with a better retention of air and, more importantly, noticeable improvements in organoleptic properties. Again, the use of cream, rather than butter oil, has not surprisingly produced better organoleptic properties, but has further, and more importantly, had considerable advantages in quality control in that rancidity, which was heretofore a problem with butter oil, has been eliminated. Further, there is no need to heat, for example, butter oil and thus, the process is less time consuming and expensive than heretofore.

Additionally, the particular manner in which the ice-cream is frozen, namely, by ensuring there is no unit greater than a size of 4 litres in volume, is advantageous as by keeping the size relatively small, the actual distance between the outside of the container holding the ice-cream and the inner core of the ice-cream is always relatively small so that the blast freezer operates very quickly on the ice-cream, ensuring even freezing and preventing the formation of ice crystals within the ice-cream. This may seem a relatively simple way of solving the problem, however, it is one that has not been carried out before, nor indeed has it been appreciated by those in the industry.

Furthermore, by placing the individual containers in a spaced-apart relationship in a freezer, this ensures adequate direct exposure of the exterior of each container.

The freezing process is further enhanced by circulating air around the freezer. it has also been found that by use of a bacterial filter, the resultant analysis of the ice- cream has led to a much safer and better food product.

Detailed Description of Invention The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 is a layout of an ice-cream making plant according to the invention, and Fig. 2 is a perspective diagrammatic view of a portion of the plant, Referring to the drawings and initially to Fig. 1 thereof, there is illustrated an ice-cream making plant, indicated generally by the reference numeral 1, comprising an initial preparation stage 2, a conditioning stage 3, a product forming stage 4, a freezing stage and a cold storage and packaging stage 6. Briefly, and as will be described in more In the conditioning stage 3, the ingredients are held prior to further freezing and mixing in the detail below, in the preparation stage 2, all the ingredients are mixed. product forming stage 4 where various products such as ice—creams on sticks, ice- creams in blocks, ice—creams in tubs, and so on, are prepared. Then, in the freezing stage 5, a quick final freezing is carried out of the product which is still in relatively small sizes and as will be described below, none greater than 4 litres in size, when it is then delivered to the cold store and packaging stage 6 for final packaging and holding until it is dispatched.

Referring again to Fig. 1 and to Fig. 2, there is provided an ingredients storage area 10 from which are fed to a pair of tri-blender mixers 11, each having a dry ingredients and a liquid ingredients inlet. The tri-blender mixers 11 in turn feed a homogeniser 12 and then from a heat exchanger 13 to a conditioning stage 3. The tri-blender mixers 11 are simply paddle mixers with a recirculation pump such that the ingredients are continually recirculated within the mixer or blender as the paddles operate to mix the ingredients.

The tri-blender mixers 11 are also jacketed blenders with an outer layer skin for heating with hot water. The homogeniser 12 is a standard homogeniser, as is the heat exchanger 13 which is again a standard plate heat exchanger.

The conditioning stage comprises a plurality of holding tanks 15, each incorporating mixers (not shown).

The product forming stage 4 comprises a plurality of continuous freezers 20 each feeding a separate product forming station such as a lollipop forming station 21, a tube forming station 22, a sliceable block forming station 23, a rectangular plastics tub forming station 24 and a cylindrical tub forming station 25. Each continuous freezer 20 comprises a pump and bacterial filter unit 26 feeding a continuous freezer chamber 27 which includes a mixing unit. The lollipop forming station 21, the tube forming station 22 and the cylindrical tub forming station 24 feed a blast freezer 30, while the sliceable block forming station 23 and the rectangular plastic tub forming station 24 feed a blast freezer 31, the blast freezers 30 and 31 forming the freezing stage 5. These in turn feed the cold storage and packaging stage 6.

The blast freezer 30 is of lesser capacity than the blast freezer 31. Essentially, the product forming stations 21 to 25 are simply filling stations.

In operation, the various ingredients, both dry and liquid, are stored in the preparation stage 2 in the ingredients storage area 10. They are then delivered to the tri-blenders 11 where the mixture is heated firstly to about 60°C to ensure that all the ingredients blend naturally. In accordance with the invention, there is prepared a base starter liquid of cream, milk and water which is at least 50% by weight of skimmed milk.

Various solid ingredients including sugar, stabilisers and emulsifiers and indeed, in certain cases, flavouring ingredients. are added while the mixture is heated to between 45°C and 60°C. It generally is not raised to above 60°C. The amount of heat depends entirely on the mix and is chosen dependent on that. Usually, it is mixed for between 10 and 20 minutes.

It is then delivered to the homogeniser where it is further mixed. This disperses the cream evenly throughout the mixture.

The mixture is then delivered to the heat exchanger where it is first pasteurised at a temperature greater than 82°C for between 13 and 17 seconds. Then, the pasteurised liquid is cooled, generally in two stages. Firstly, the temperature is dropped to about °C and then it is dropped to less than 7°C, and often as low as 4°C, and then pumped directly to the conditioning tanks in the conditioning stage 3 where the liquid is retained for between 4 and 48 hours.

After the liquid has been conditioned, the liquid is then sent from the tanks 15 to one or other of the continuous freezers 20. Then there is carried out an initial freezing process to freeze the mixture to between -3 and -7°C and because of the ingredients, it is still malleable at this temperature. Therefore, strictly speaking, it is not a frozen mixture.

During this initial freezing process, air is added at a pressure of between 3 and 4 bar, through the bacterial filter 26. Then, the mixture is delivered to one of the stations 21 to where. for example, the individual Iollipops are formed or individual tubs are filled, or individual blocks of ice-cream in packaging is provided. While individual Iollipops, for example, may be packed into small containers, at no stage do any of the containers exceed 4 litres in capacity. In this way, what is delivered to the blast freezers 30 and 31 are relatively small individual containers. The individual containers are placed in a spaced-apart relationship in the freezer to ensure adequate direct exposure of the exterior of each container. Thus. a relatively large surface area relative to the volume of the container is exposed in each blast freezer 30 which means that the penetration required from the freezer, to ensure the interior of the container is quickly frozen, is relative short. It is a short freezing passageway and in this way, the contents of each of the individual containers is quickly brought down to a lower temperature. The temperature of the individual packages or containers is reduced to between —20°C and °C within a period not exceeding three and a half hours. However, the major feature is that this is a relatively even freezing. It is not one where the interior of the container is only frozen, for example, in the last quarter of the freezing time but there is a quick freezing of all the contents. This inhibits the formation of ice crystals or at least large ice crystals. Then, the individual packages or containers are delivered from the freezing stage 5 to the cold storage and packaging stage 6 where further packaging may take place and the ice-cream is stored until it is delivered to customers.

Table 1 illustrates some sample mixes that may be provided.

Table 1: Sample Batches of Ice-Cream with Varying Levels of Skimmed Milk Liquid Batch A B C Water 55.70 27.80 5.48 Cream 14.30 14.30 14.30 Skimmed Milk Liquid 0.00 30.00 54.00 Sugar 12.00 12.00 12.00 Skim Milk Powder 8.20 6.10 4.42 Vegetable Oil 5.00 5.00 5.00 Glucose Syrup 4.00 4.00 4.00 Emulsifier/Stabiliser 0.50 0.50 0.50 Flavouring/Colouring 0.30 0.30 0.30 TOTAL 100.00 100.00 100.00 Fat 10% 10% 10% Milk Solids Non Fat 9% 9% 9% Total Solids 35% 35% 35% Example 1: Effect of freezing time and air circulation on organoleptic properties of sample ice-creams.

Procedure: Ice-cream batches were prepared as described previously using standard ice-cream mixes A. B and C, from Table 1.

Each batch was placed in containers of 2 litres each.

Batch A was frozen to between -20°C and -25°C for a period of 3.5 hours.

Batch B was frozen to between -20°C and -25°C for a period of 12 hours.

Batch C was frozen to between -20°C and —25°C for a period of 25 hours.

Furthermore, Batch A was subjected to air circulation during freezing.

The results are illustrated in Table 2 below.

Table 2: Effect of freezing time and air circulation on organoleptic properties of sample ice-creams Batch smoothness Creaminess Body Ice Crystals Average Comments Evidence A 9 10 8 10 9.2 Smooth and creamy B 7 6 5 7 6.2 Slightly cold mouthfeel, light body C 4 4 5 4 4.2 Cold mouthfeel, not creamy, ice crystals evident The organoleptic assessment was carried out by a taste panel of 12 people who were asked to rank the samples out of 10, wherein 10 is the most preferred and 1 is the least preferred sample.

Therefore batch A yielded the most favourable results indicating that a shorter freezing time and the presence of air circulation are favourable.

Example 2: Effect of using skimmed milk liquid as a substitute for skim milk powder in sample ice-creams.

Procedure: Ice-cream bathes were prepared as described previously using standard ice-cream mixes A, B and C from Table 1.

Each batch was placed in containers of 1 litre each. after initial freezing.

Each batch was frozen to -20°C within a period of 1.5 hours.

Each batch was subjected to air circulation during freezing.

The results are illustrated in Table 3 below.

Table 3: Effect of using skimmed milk liquid as a substitute for skim milk power in sample ice-creams.

Batch Creaminess Texture Body Average Comments A 4 6 3 4.3 Light body, smooth but slightly cold texture, not a creamy flavour.

B 7 7 5 6 3 Medium body, smooth texture, moderately creamy flavour.

C 9 8 8 83 Full body, smooth texture, creamy flavour.

The organoleptic assessment was carried out by a taste panel of 12 people who were asked to rank the samples out of 10, wherein 10 is the most preferred and 1 is the least preferred sample.

Therefore batch C yielded the most favourable results indicating that ice-cream with a higher proportion of skimmed milk liquid has improved organoleptic properties.

Example 3: Physical assessment of sample ice-creams Ice-cream batches from Example 2 were further subjected to melt-out and whippability tests.

Melt Out Each batch was tempered overnight to —18°C. g of ice-cream was placed on a wire mesh rack at room temperature.

The time taken for the ice-cream to melt into a dish under the rack was measured. The melted ice-cream was examined for texture. The desired melt out time is 15 minutes.

The desired texture is smooth with evenly sized air bubbles. whippability Liquid ice-cream mix was aged for 6 hours. It was transferred to a laboratory mixer. It was mixed at high speed for 2 minutes. The overrun was measured. A higher overrun is desired with even textured air bubbles. Large air bubbles are not desired.

The results are illustrated in Table 4 below.

Table 4: Physical assessment of sample ice-creams Therefore, batch C has the most favourable melt out and whippability characteristics.

Batch Time to melt Melt down Whippability Whipping out characteristics characteristics A 11.5 minutes Smooth and creamy 36% Large foamy air cells B 13.2 minutes Smooth and creamy 43% Uneven textured air cells C 15.5 minutes Smooth and creamy 55% Even textured small air cells

Claims (2)

1. A process for making ice-cream comprising the steps of:- preparing a base starter liquid of cream, milk and water and at least 30% weight by weight of skimmed milk; mixing the base liquid and solid ingredients including sugar, stabilisers and emulsifiers, while heating the liquid to between 45°C and 60°C for between 10 and 20 minutes; pasteurising the liquid at greater than 82°C for between 13 and 17 seconds; cooling the pasteurised liquid to less than 7°C within two hours; retaining the liquid to condition the liquid for between 4 and 48 hours; freezing the mixture in an initial freezing process to between -3°C and - 7°C, while adding air at a pressure of between 3 and 4 bar after delivering the air through a bacterial filter; filling the ice-cream, so produced, into individual containers of a size not greater than 4 litres; placing the individual containers in a spaced apart relationship in a freezer to ensure adequate direct exposure of the exterior of each container; and freezing the individual containers to between -20°C and -25°C within a period not exceeding three and a half hours.

2. A process as claimed in claim 1, in which the amount of skimmed milk exceeds 50% by weight of the base starter liquid. A process as claimed in claim 1 or 2 in which the liquid is conditioned for between 12 and 18 hours. A process as claimed in any preceding claim, in which the initial freezing is within the range —3.5°C to -4°C. A process as claimed in any preceding claim, in which the mixing and pasteurising of the base liquid and solids comprises:- mixing and heating the base liquid in a mixing tank; homogenising the product in a homogeniser; delivering the homogenised liquid to the heat exchanger to pasteurise the liquid; and then cooling the liquid in the heat exchanger. A process as claimed in any preceding claim, in which the skimmed milk has a fat content of between 0.10% and 0.15% w fat. A process as claimed in any preceding claim, in which, additionally, skim milk powder is added. A process substantially as described herein with reference to and as illustrated in the accompanying drawings.