The first product to be aerated commercially was Ice cream. This was done primarily to make the product softer (for scooping and dispensing). There were also significant commercial benefits associated with selling air. Whipped Ice Cream can typically be whipped to 100 % overrun and labelling legislation is the main restriction on the amount of air that can be added.
In the manufacture of "Dairy Desserts" aeration is used to modify mouth feel, texture and flavour delivery in addition to the commercial benefits previously mentioned. The degree of aeration can be used to alter the product characteristics to such an extent that the same base could be perceived as either low quality or premium.
(The quantity of air held by the product (%) is called the % Overrun.)
The Science of aeration
Cream with a fat content above 30% can be whipped very easily using low powered whisks and then folding in purees and fruit
An unhomogenised cream fat globule is very irregular in size and shape and is composed of layers:
Cream is reliant on fat and protein in the system to form a structure which is capable of holding air. The fat must be in its solid state - even a minute amount of liquid fat will interfere with aeration. The proteins dissolved in the aqueous phase of the cream stabilise the system. If the conditions for aeration are not correct (particularly the temperature, which allows the fat globules to cluster) the cream will not whip or will end up as a mixture of butter and buttermilk. This is why the pipe work and all contact parts must be chilled prior to contact with a fat based system.
Fat globules cluster together in the bubble walls, where the surface forces rupture some of the membranes. The exposed spheres of fat then stick to each other and form a rigid but delicate network. The proteins then create a matrix to bind the fat together which increases its ability to hold air. Milk can not be whipped because the fat globules are fewer. A froth can be achieved but this disappears very quickly as the fat globules are too far apart to stick together.
Large fat globules aerate far more readily than small fat globules as they produce a stiffer whip. This is why homogenised cream is never used. Jersey and Guernsey cows produce the best milk for aeration as the fat globules are larger and the protein content is higher.
Stabilizers are added to the cream to give the stability required over the shelf life of the product.
A stabilizer directly impacts the product quality and shelf stability. The system should be able to stand up to transportation over long distances - and even altitudes. Every stabiliser system will contain an emulsifier from a group called "mono - diglycerides." Other components of the system may be Starch, Gelatine, carrageenan, Guar gum, Xanthan gum and locust bean gum. As with the fat based systems, cooling and ageing allow the fat globules to cluster. In stabilised systems the emulsifier crystallises inside the fat. The proteins hydrate and form a structure which binds the fat and usually results in a substantial increase in viscosity which allows for better absorption and holding of the gas. The increase of viscosity and the gel network formed by the stabilisers and emulsifiers during the ageing time should guarantee homogeneous gas bubble distribution if the product is at the correct temperature.
There are many commercial methods of aerating products currently available on the market, however, the most common by far is mechanical aeration as utilised by machines such as Mondomix, shufflemix and Tanis. The machines vary somewhat in their design - but the principles of their operation are the same.
How does the equipment work?
Unaerated product enters the whipping head. This comprises of a stainless steel shaft covered with metal pegs which fit inside a housing that has also has pegs inside of it. When assembled the pegs on the shaft and on the inside of the head interlock. The clearances are very tight and if the unit is not assembled properly the pegs will hit each other and break. The whipping head should always have a chilled water jacket on it. The purpose of this is not to cool the base being aerated but to prevent the uptake of heat energy that would be generated by the rotation speeds inside the head. Whilst inside the head the air is injected. The mixing head mechanically crushes the large gas bubbles into very small bubbles that are trapped within the protein / fat matrix. The bubble size is key to determining the product attributes. The product then passes into the backpressure regulator. This needs to be balanced to the mixing head pressure. If the pressure is too low the whip will be lost as the base will be unable to hold the whip. If, however, the pressure is too high the air will be squeezed out of the product. Vertical pumping of the aerated base, bends in the pipe and depositing can result in loss of overrun between the aerator and the depositor hopper.
Mondomix Operation, www.mondomix.nl
Check tank temperature & standing time. If either is not correct inform the line manager and Technical. Even if a product overrun is achieved it will collapse on Transit if the standing time is incorrect. Check the chilled water supply to the mixing head is connected and turned on. Check the air is turned on (system pressure should be 6 bar).
Achieve Correct Overrun:
Pump unaerated product through the system Set the rotor speed to an acceptable level on the mixing head. The value will vary depending on the size of the aerator. A low value (usually one third of the maximum rotor speed) should be selected for set up - particularly for high fat products or products containing chocolate. Set the air injection and adjust the back pressure until the correct overrun / density is achieved. The back pressure is usually set at 2 bar and should not exceed 3 bar.
Critical Parameters that will dictate aeration characteristics:
Incoming product temperature - Product should be aerated at the temperature noted in the work instructions. If the product is to warm there will be issues with achieving the overrun in the first place as well as maintaining the definition over the life of the product. Generally, the colder a product is the better it will whip.
During the standing time (or ageing in cream) the components (fat or stabiliser) develop a structure. This usually manifests itself as an increase in viscosity. The matrix that develops gives the product its ability to hold air.
Should always be 6 bar.
This controls the quantity of air injected to the mixing head.
Mixing Head Speed
The mixing head speed determines how well the air is incorporated into the product. Two products at the same Overrun can be wet or dry. This is due to the bubble structure.
Generally somewhere between 2 bar and 3 bar. Back pressure should not exceed 3 bar as the air can be squeezed back out of the product.
This guide is only relevant when product arrives within specification.
Problem Symptom Cause Action *Wet Whip Correct Overrun - Wet product Bubble Structure too large Increase mixing head speed. If product is still wet increase back pressure (not beyond 3 bar) Dry Whip Correct Overrun - Dry product Bubble structure too small Decrease mixing head speed. Overweight Too heavy Overrun too low Increase air until correct Underweight Too light Overrun too high Decrease air until correct Poor incorporation Product popping and spluttering from the pipe Air not being fully incorporated Increase or decrease the Rotor speed. Adjust the air injector (too much air can cause this) Adjust the back pressure (Air can be squeezed out of a system). Poor presentation Product different colours Generally after stoppage where pipe walls increase in temperature Purge lines and reset Overrun.
· High mixing head speeds will cause the cream to butter and Chocolate products to have a grainy mouthfeel.
It is important to adjust one variable at a time and wait for the adjustment to take effect.
What is Overrun?
Overrun is the percentage of air incorporated into a product.
% Overrun = Unwhipped base weight - Whipped base weight X 100 Whipped Base weight
Overrun and Density are directly proportional
What is Density?
Density is the volume occupied by a given weight of product. The amount of space occupied by the product will increase with the quantity of air incorporated. The weight will remain the same (as the air weighs nothing).
An overrun of 100% will double the volume occupied by the unwhipped base.
Presented by David Northeast of
USP Innovation Consultants
(Tel: 01672 870039 Mobile: 07919 074500) firstname.lastname@example.org
N.E.M Business Solutions Tel / Fax : 01823 680119 Mobile 07768 981196