The Mixing Process
There are several processes which occur during the mixing of the dough. These include:
- Dispersion of all the ingredients and blending into a homogeneous mass
- Hydration of the flour
- Emulsification of the fats and water
- Development of the gluten formed by the proteins in the flour
- Activation of leavening agents
Crackers and hard doughs
Crackers and hard doughs have relatively high amounts of water and small amounts of fat and sugar. During the mixing process, the gluten is developed by a vigorous cutting and shearing of the dough. This results in an extensible dough suitable for sheeting and cutting to form the dough pieces. The mixing action imparts work to the dough and results in an increased temperature. In order to ensure consistency of dough batches, the dough for products such as semi-sweet biscuits are mixed to a fixed pre-set temperature.
For most products the process is an “all in” mix, when all the ingredients are fed to the mixer at the start. After mixing cracker doughs will be fermented. The process for soda crackers, the mixing process is in two stages.
For soda crackers the initial mixing is with approximately 2/3 of the flour quantity and half of the fat. The initial mix results in a “sponge” which is fermented for 12 hours. The remainder of the flour and fat is then added, with soda and salt and the dough is then fermented for a further 12 hours. The process is known as “sponge and dough”.
Short dough biscuits
In mixing short doughs it is important that the gluten is not developed. The mixing is therefore in two stages. The first stage is called a “cream up”. During this stage the fat, sugar, water and small ingredients are mixed to obtain a soft mass. The flour is then added and the final stage of the mix is as short as possible so that the gluten web is not developed and the resulting dough has a short texture. After mixing the dough will be stood for approximately 30 minutes to allow the hydration of the flour before forming.
Cookie doughs have high fat and sugar. The doughs are soft and they are formed by extrusion and depositing directly onto the oven band. As for short doughs, the mixing process is in two stages, with a “cream” stage, followed by adding the flour and mixing for a short time to prevent gluten development. The doughs are kept cool and usually mixed to a temperature of around 20ºC.
Deposited cake batters, creams
Biscuit creams and deposited Jaffa cake
Doughs for snack cakes, soft cookies and biscuit creams may be mixed on a planetary mixer which provides a whisk and aeration to give a very light, low density, fluid dough for depositing and creams suitable for sandwich biscuits.
Types of mixer
There are five main types of mixer, each with advantages for particular products and applications: Vertical spindle mixers, High speed horizontal mixers, Horizontal mixers for cookie doughs, Continuous mixers and Planetary mixers.
Vertical spindle mixers
These mixers use a mobile dough tub into which the ingredients are fed and the vertical spindles are either lowered into the tub or the tub is lifted to the spindles.
Vertical spindle mixer from Apinox Srl. This picture belongs to Apinox Srl – Italy. This mixer has been specifically designed for the production of soda cracker, cream cracker with two stages, fermented dough and delicate dough.
Vertical spindle mixers are widely used for fermented crackers, particularly soda crackers. The dough is mixed in the tub and the tub can then be transferred to the fermentation room. After fermentation, the dough tub is brought back to the mixer for the final stage of the mixing cycle. All the ingredients are fed to the tub from a weigh hopper or manually. In a two stage mixing process for soda crackers, additional ingredients may be added before the final mix.
The mixing action is slow and thorough and generates little heat. Hard doughs may require a total mixing time of 60-90 minutes to develop the gluten sufficiently.
Horizontal High Speed Mixers
This type of mixer is very widely used for a variety of snack crackers, semi sweet doughs and short doughs.
The main dry ingredients may be fed from an automatic weigh feeding system mounted above the mixer. Water and other liquid ingredients may be metered and fed automatically. Typically small ingredients are fed to the mixer bowl in a half tilt position by hand.
The mixer bowls are stainless steel with a water jacket through which cold water is circulated. For special snack products, heated jackets may also be used to gelatinise potato starches.
The bowl tilts to discharge the mixed dough. The tilt may fully invert the mixer bowl to allow automatic discharge of dough directly to a hopper below the mixing floor for feeding the sheeter of the forming equipment.
Baker Perkins mixer capacities range from 450kg to 1100kg. Two speed machines have timers to set times at slow speed (30rpm), then high speed (60rpm). Alternative drives are variable speed.
Baker Perkins High Speed Horizontal Mixer
Some hard doughs are mixed to a pre-set temperature. The mixer blade provides a vigorous extruding and shearing action to develop the gluten web and this action results in an increase in temperature. The dough temperature is monitored by a thermocouple in the wall of the mixer bowl.
The shaft-less mixer blade design gives an end to end mixing action to incorporate all ingredients evenly including those fed in small quantities. It avoids dough adhering to a central shaft, which is not fully incorporated in the dough mass on discharge.
Horizontal mixers from Spooner Vicars have a helical “Sprag” mixer blade, which allows the temperature sensor to be incorporated in the centre of the dough mass.
Horizontal mixers for cookie doughs
Sigma Arm mixers have been an industry standard for mixing cookie and biscuit doughs for many years. Mixers have stainless steel construction, fully tilting bowl with water jacket for temperature control and two speed drives or variable frequency drive.
Continuous mixers have been successfully used for a wide range of cracker, biscuit and cookie doughs. They are supplied with fully automatic ingredient feed systems and usually for single purpose production lines.
The LDX Continuous Mixer combines all minor ingredients and a portion of the required flour in the first mixing stage. In this stage, special mixing elements cut the fat into the other ingredients. In the final stage, the remaining flour is added to create the final dough. This mixer is ideal for most types of cookies or any application where ingredients are blended before flour is added.
Tonelli Planetary Mixer
The mixing bowls are mobile and ingredients may be fed remotely.
The mixer may be fitted with suitable interchangeable tools for a variety of applications, including cookies, cakes and creams. The planetary mixing system uses one or two mixing tools with a scraper. These are rotated on a pre-set planetary system to suit the product. The mixing speed of the tools and the rotation are separately driven.
The mixer has a facility to inject air into the mix to create a light, low density cake batter.
The dough may be transferred by pump or by lifting and tilting unit to feed the hopper of a depositing machine.
Baker Pacific Ltd. 2016
Apinox S.r.l. www.apinox.it 2016
Baker Perkins Ltd. www.bakerperkins.com 2016
Dong Yang Food Machinery. www.mixer.co.kr 2016
The Middleby Corporation www.middleby.com 2016
Oakes www.oakes.com 2016
Peerless Food Equipment www.peerlessfood.com
Reading Bakery Systems www.readingbakery.com 2016
Spooner Vicars www.spoonervicarsbakery.com www.middprocessing.com 2016
Tonelli www.tonelli.it 2016
T.L. Green www.readingbakery.com 2016