High Speed Mixing, Your Baking Fix

For high output bread bakeries, mixers that are reliable, consistent and economic are crucial. Operating at outputs that can exceed 10,000 loaves per hour from a single production line, a secure supply of mixed dough of the necessary quality is critical to maintaining production without costly stoppages or product waste.

Clearly, the right choice of mixer is fundamental: it must be part of an overall system meeting output, cost and efficiency targets while maintaining quality and flexibility.

High-speed mixing is a technique rapidly increasing in popularity. Speed is the key to a number of fundamental advantages which lead to consistent high quality at an economic price.

Because the mixing process is rapid and batch sizes are small for a given output, the dough can be passed through the divider to the prover while it is fresh and before fermentation can begin. This ensures product consistency.

For mixers that can mix a batch of dough fast, production efficiency can also be achieved—while one batch is mixing, another can be weighed out. Allowing for loading and discharge, more than 10 batches per hour each of between 170 and 385 kg can be produced this way.

High-speed mixers can produce better quality dough with lower quality flour than any other process because mixing is much more thorough. A combination of a high-speed beater and baffles on the periphery of the mixing bowl work a much higher percentage of gluten molecules in the dough at any one time during the key dough development stage of the process. In spiral and roller bar mixers, by comparison, only a relatively small number of molecules are worked at any one time.

Dough development is the key phase in mixing. It involves stretching gluten molecules so that a proportion of them break, and then reform as cross-linked bonds with other gluten molecules. This builds a network of gluten that gives dough its elasticity.

The rate at which dough develops is directly related to how quickly molecules can be broken and bonds re-formed. This rate can be optimised for throughput and quality in a high-speed mixer by controlling the rate of energy input to a value that is specific to the flour being used and the product being made. Developments in process control have eliminated batch to batch variation and if the line stops for any reason, the amount of dough rejected is minimal and re-start extremely rapid.

As well as mixing the dough horizontally, the bowl of a high speed mixer is shaped so that it also generates a vertical motion—a 3D mixing action is present in all parts of the mass at all times.

High-speed mixers carry out the same process as other machines, but they work all of the dough simultaneously, not merely part of the dough, and they can also do this much more quickly. They make the most of the protein present, such that the strength of dough from a high-speed mixer using lower protein (and cheaper) wheat is the equal of dough from other mixers using costly, high-protein flour.

Roller bar and spiral mixers can normally achieve only three mixed batches per hour: the consequence is that the time elapsed before the dough reaches the prover will vary considerably, giving the dough time to ferment, leading to inconsistency in quality. Dough can be rising in the divider hopper which adversely affects scaling accuracy.

Spiral mixers, incidentally, have another major disadvantage. They output small batches which involves the use of numerous mixing bowls. This tends to be an inefficient, complicated, and wasteful technique in space and labour terms. The location of the beater above the bowl means that the bowl often has to be removed to feed the ingredients in, and removed again to discharge the mixed dough.

A high-speed mixer by comparison is compact and space efficient. The mixing bowl typically tilts for dough discharge, achieved with the help of the beater located in the bowl. Dough moves seamlessly from bowl to tub to divider.

To achieve a comprehensively developed and thoroughly mixed dough in a high-speed mixer, the use of pressure and vacuum sequentially can be incorporated into the mixing cycle. By pressurising the bowl in the first mixing phase, more air is added, providing oxygen to enhance the action of ascorbic acid. This improves the development and gas retention in the dough. Vacuum in the latter stages helps create very precise control over the size of bubbles in the dough to refine the crumb structure of the finished product.

This means that a range of textures can be produced, from close-grained tin bread (typical of the UK and USA markets) to open baguettes and everything in between. In fact, most types of bread dough can be handled—white, wholemeal, wholegrain, rye, sour dough, as well as brioche and pizza.

A high-speed mixer is also an ideal machine for producing dough for burger buns—a rapidly growing product worldwide. Equipment for the automatic addition of a liquid sponge process can easily be installed. High-speed mixers also offer completely variable speeds for mixing which ensures appropriate mixing speed at every stage of the process. This is essential especially in the early stages, where mixing speed is crucial to good hydration of the flour.

Today’s high-output bakeries require comprehensive, automatic control systems. The high-speed mixer has a clear and informative touch-screen human-machine interface, with process visualisation to let users know what is happening at every point at any time. Well-structured software and industry standard hardware are reliable and supported worldwide.

Control includes automatic management and adjustment of both recipes and scheduling, even after stops. Recipes may be stored locally or downloaded from a higher level system; changes can be implemented without delay at the next batch. The dynamic scheduling system monitors dough use and will programme one or a pair of mixers to provide a constant feed of dough without long resting periods, and without gaps in supply.

There is a comprehensive reporting system with excellent connectivity to external systems. Fault finding is made easier by alarm filtering that displays only primary alarms so that operators can trace the source of problems without being side-tracked by downstream alarms. Process alarms alert operators to potential parameter variations that might affect the dough.

Maintenance scheduling covers all critical areas, such as bearings, which require regular maintenance based on time or cycles; usage can be monitored and the system can provide prompts to engineers when maintenance is required. Daily maintenance lists and checks for the operators are also included.

Hygiene and maintenance in a world of demanding environmental and safety requirements have assumed significant importance when choosing a mixer. High-speed mixers that have been developed in accordance with hygienic design principles can minimise levels of dust, water and dough debris, and make that which does accumulate much easier to see and remove completely.

A wash-in-place system for the mixing bowl and lid can be introduced, which would make for a much quicker and more thorough cleaning process than the conventionally used manual cleaning. Water can be fed by pressure jets via a retractable hose within the bowl, fitted to the beater by the operator whenever cleaning is required. A self-clearing valve can ensure the bowl drains completely with no dough leftovers.

A wash-in-place containment area can also be included for liquid ingredients. Washing out pipework has the potential for water and yeast leaks, and the containment area would ensure all liquids stay within a defined and easily cleaned area.

As far as maintenance is concerned, a simplified arrangement of components and associated pipework and cables would mean better access and easier tasks. Calibration routines would also be much quicker and simpler.

Noise levels are assuming a higher health and safety profile. The pressure vacuum pump can be designed for quieter operation, and mounted on a skid that can be located in a separate room or soundproof enclosure, if required.

Noise from the main drive can be reduced by using a high performance belt with reduced contact area, while the motor and bowl can sit in machined locations on the swing frame to ensure they are perfectly aligned. Easily removable covers can provide users with good access to the main drive motor chamber for maintenance and cleaning.

While meeting bakers’ needs in terms of hygiene, ease of cleaning and minimum maintenance time, a high-speed mixer such as one by Baker Perkins can also meet all legislative standards, including ATEX—the directive from the European Union dictating what equipment can be used in an explosive environment—where necessary. Materials are all compliant with good manufacturing practices and surfaces near or in contact with the product are in stainless steel, many with a food grade coating.

The high-speed machine can be more than just a mixer: it can be a system fully automated from ingredient feed to delivery to the divider. It is designed as an integral part of a complete mixing and forming plant and a key element in automating the complete production system.

Precise mixing, accurate weight control and gentle dough handling all contribute to performance that drives bread quality up and production costs down. Gentle treatment is identified by bakery industry research into dough rheology to be a significant contributor to superior product excellence and value.

Throughout the world, experience in tough production environments shows that the objectives of improved consistent quality, reduced ingredient costs and a clean label can all be achieved simultaneously.

Highly automated systems are often associated with products of lesser quality, yet there is now absolutely no reason why this should be the case. Unit mixing and forming machines may be installed individually on existing lines, and are all capable of matching or even improving on the consistency and quality of products from manually operated machines. They can be installed as part of a manual, semiautomatic or fully-automatic system.