Application Reports

Preparation of Ice Cream Mixes

Ice cream mixes are formulated from either whole milk, skim milk, cream or in some cases water, with a number of added ingredients.

 
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The Process

A typical mix would be prepared in the following manner: 

  • Liquid ingredients are weighed/metered into the process vessel. Heating follows to aid melting of the fat and dissolving/hydration of subsequent ingredients.
  • Powdered ingredients - skim milk powder, sugars, whey powder, etc. are added to the liquid and mixed until dispersed.
  • Stabilizing and emulsifying agents are added. These may be dry premixed with other ingredients, (e.g. sugar) to reduce particle agglomeration and “weight” the powder to aid incorporation into the liquid.
  • Fat is added. Butter or other solid fats may be melted in a separate vessel before addition to the mix. 
  • The mix is pasteurized at around 185ºF (85ºC).
  • The mix is homogenized, usually by passing through a high pressure homogenizer. 
  • The product is then “aged” in a holding (or ripening) tank to allow the stabilizing agents to hydrate and the fat to crystallize.
  • Flavor and coloring may be added at this stage. 
  • The finished mix is frozen in special freezers which whip a controlled amount of air into the mix.

 

In many countries, legislation covers the composition and labelling of products. These regulations restrict the use of certain ingredients and specify minimum content of the fat and total solids.

The Problem

Mixing powders into liquids is one of the most difficult mixing operations. The process is subject to a number of problems when using conventional powder/liquid wetting systems and agitators:

  • Powder must be added at a controlled rate to reduce agglomeration of particles.
  • Premixing of powders increases labor costs and process time.
  • SMP, whey powder and cocoa powder (used in chocolate ice creams) are very cohesive, making handling and controlled powder addition difficult.
  • Stabilizing and emulsifying agents have an even greater tendency to agglomerate and require special handling.
  • Conventional systems do not produce sufficient shear to break down agglomerates.
  • Long processing times are required to complete dispersion and achieve a satisfactory consistency.
  • Cocoa (where used) needs to be thoroughly wetted and “cooked” to prevent it imparting a “gritty” or “floury” texture to the ice cream.

The Solution

The above problems can be overcome by using a Silverson High Shear Mixer. Operation is as follows: 

Stage 1

The high speed rotation of the rotor blades creates a powerful suction which draws the liquid and solid/powdered ingredients into the workhead. These can be added without the need for pre-mixing.

Stage 2

The materials are subjected to intense shear in the confined area of the workhead. Agglomerates are broken down in the gap between the rotor blades and stator wall.

Stage 3

A lump-free mixture is rapidly obtained. The product is forced out of the stator as fresh material is drawn into the workhead. A circulatory mixing cycle develops in which all the material passes through the Silverson workhead.

The Advantages

  • Premixing of powdered ingredients is not necessary.
  • Agglomerate-free mix.
  • Stable emulsion.
  • Rapid mixing times. 
  • Maximized yield of raw materials as thickening agents are fully hydrated and other ingredients are properly dispersed.

 

The batch size, formulation, type of ingredients and the viscosity of the mix dictates which machine from the Silverson product line is suited to individual processing requirements: 

Silverson Flashmix

  • Ideal for larger batches
  • Capable of rapidly incorporating large volumes of powders
  • Minimized aeration
  • Minimized cleaning requirements
  • Suitable for higher viscosity mixes
  • Suitable for operation at higher temperatures
  • Minimum operator input required

High Shear In-Line Mixers

  • Ideal for larger batches
  • Easily retrofitted to existing plant
  • Must be used in conjunction with an efficient in-tank agitator to wet out powder
  • Aeration free
  • Self-pumping
  • Can be used to discharge vessel
  • Ultra Sanitary models available
  • High Viscosity models available

High Shear Batch Mixers

  • Suitable for batches up to 300 US gallons
  • Can be used on mobile floor stands
  • Can easily be moved from vessel to vessel

Silverson Ultramix

  • Excellent in-tank movement
  • Capable of rapidly incorporating large volumes of powders
  • Ultra Sanitary CIP design
  • Ideal for higher viscosity mixes
  • Low maintenance

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