Hygienic design involves the following elements:1
- Materials of construction
- Stainless steel
- Polymeric materials
- Thermal insulation materials
- Functional requirements
- Cleanability and decontamination
- Prevention of entry and growth of microorganisms
- Compatibility with functional and operating requirements
- Validation of the hygienic design of equipment
- Hygienic design and construction
- Surfaces and geometry
- Surface finish/roughness
- Drainability and layout
- Testing hygienic characteristics (e.g., cleanability)
The fundamental objective of hygienic design is the prevention of contamination or adulteration of the baked goods. Contamination can come from raw materials (introduced into the processing environment), but the products can also be contaminated by the processing and packaging environment inside the plant.
As an example, if a piece of equipment has an inadequately hygienic design, it will be difficult to inspect, maintain, clean, and/or sanitize. The residues (e.g., dirt, soil, and debris) can be retained in the cracks, crevices, and dead spaces of it and allow microorganisms it harbors to survive and multiply. These biological hazards may then cross-contaminate subsequent batches of product.1
Bakeries need to properly incorporate hygienic considerations into the traditional technical requirements set in the initial stages of the design or purchase phase of equipment. Although it is not always easy and practical to follow this approach, the search for a comprehensive or “harmonic” set of requirements is necessary to avoid any endangerment of food safety. The long-term benefits of doing so are not only product safety, but also the potential to increase equipment life expectancy, reduce maintenance and, consequently, reduce operating costs.2
This way, bakeries can reconcile and/or balance technical, operating, and budget requirements with hygienic expectations when acquiring new processing equipment or designing lines. Considerations include:
- Throughput (installed capacity)
- Size (relevant to use of floor space)
- Possibility of proper linkage/synchronization with the existing stages/flows within the production line
- Energy consumption (electricity, gas fuel, or a combination of these)
- Maintenance requirements and costs
- Automation level (degree of control and interaction between machine and operator)
- Price (cost of equipment plus commissioning and other charges)
- Hygienic design
The strategy for designing, constructing and installing hygienic equipment/machinery requires the following considerations:
- The intended use of the equipment (delimitation of usage in terms of products and processes)
- Identification of food safety hazards (chemical, biological and physical) associated with the food products that will be processed/handled in the machine
- Characteristics of the products that will be processed/handled in the machine (e.g., physical state, moisture content, acidity, microbiological and physicochemical stability, sensitivity of components).
- Risk assessment associated with each hazard.
- Methods and measures regarding equipment design which can eliminate/reduce risks associated with these hazards
- Further processing that will take place (subsequent processing equipment that could eliminate/prevent a given food safety hazard, e.g., washing, baking, pasteurization, metal detection)
- Application of the product and/or the expected consumers of the product (e.g., immunosuppressed patients, infants, children, adults, elderly)
- Cleaning and maintenance activities and conditions that will be applied to the machine3
Once food safety risks have been identified, the design and construction should take these into account. Personnel and environmental safety risks should also be assessed as these may influence the final hygienic design of machinery/equipment.
It is important to apply the eight considerations mentioned above when designing, constructing and installing machinery/equipment meant for baking applications. Baking plants have unique conditions regarding food processing equipment. These often have a combination of batch- and continuous-mode stages, with open and closed equipment within the production line; usually handling low-moisture (i.e., low water-activity) products such as crackers, biscuits, wafers, and high-moisture (i.e., high water-activity) products such as bread, rolls, dough/work-in-progress).
Closed and open equipment in the baking industry
In the practice, its is easier if the machinery/equipment is classified as open or closed equipment. This way, the design, construction, installation, cleaning, maintenance, and food safety conditions can be better planned and managed:
Open equipment is that which cannot be cleaned in place (CIP), and in which the products being processed or handled are not fully enclosed (i.e., isolated from the plant environment) by a continuous wall (e.g., piping, vacuum cavities, tubing, barrels).
Open equipment often requires:
- Cleaning out of place (COP)
- Manual cleaning
- Immersion cleaning
Open equipment must be manually dismantled for cleaning. Such tasks can be performed with open plant cleaning (OPC) techniques, like foam cleaning and rinsing with medium-pressure systems (e.g., up to 40 bar). Dismantled machine parts can be cleaned in COP baths. The time required will depend mostly on validation of microbiological monitoring results. The time will vary depending on the available cleaning equipment and utensils.4
Equipment designed and constructed with its components fitted together tightly with no openings whatsoever to permit the entry of external agents (i.e., soil, human contact), and there is no possibility for accessing/touching the products held or contained by direct contact without prior dismantling.
In contrast to open equipment, closed equipment usually processes, handles, and conveys liquid and semi-solid products (e.g., process water, cleaning solutions, low-viscosity syrups, dough in bulk).
Closed equipment must be cleaned in place (CIP) due to its access restrictions and typically confined spaces.
CIP includes the following general procedures or considerations:5
- Pre-washing (rinsing with water)
- Alkaline clean
- Acid clean
- Final rinse
Bakeries make use of open and closed equipment to process a wide variety of liquid, semi-solid, and solid products. This situation is rather uncommon elsewhere in the food industry since the products usually do not radically change regarding their physical state. Baking plants are special processing environments in which chemical reactions and physical transitions take place within the production line. All these conditions must be considered when designing, constructing and/or buying equipment.
Open and closed equipment of a baking plant
||Open and/or Closed
(depending on location within production line)
- Hoppers, bins, totes
- Batch mixers/kneaders (e.g., horizontal, spiral, planetary)
- Dividers, rounders, molders
- Discrete conveying bands (i.e., transport of dough pieces)
- Packaging lines
- Pipeline for liquid ingredient transport
- Pipeline for pneumatic conveyance of dry ingredients
- Pipe fittings (e.g., elbows, tees)
- Continuous mixers
- Bulk dough conveyors (e.g., augers, endless screws)
- Pumps, centrifugal fans
|Instrumentation and control devices (e.g., sensors, actuators)
Sensors: thermocouples, pt100, humidity sensors, manometers, pH sensors, viscosity sensors, laser devices for detecting empty/filled containers
Actuators: valves, motors
Useful terms regarding hygienic design of bakery equipment
- Food-contact surface: All equipment surfaces that intentionally and unintentionally (e.g., due to splashing) come into contact with the product, or from which product or its condensate form may drain or drip down to the main product food container, including surfaces (e.g., tanks, mixers, tables, packaging materials) that may indirectly cross-contaminate food-contact surfaces or containers.1
- Dead space: Space wherein a product, sanitizing agents, or debris/soil can be trapped (i.e., become stagnant), or not be completely removed during the operation of cleaning.5
- Cleaning Out of Place (COP): Equipment is taken to a designated decontamination station for cleaning. COP requires dismantling/disassembling, washing, checking/inspecting, validating, and reassembling.2
- Cleaning In Place (CIP): Cleaning of equipment by circulation of flowing cleaning solutions, with water rinsing into and over surfaces in equipment or systems without dismantling them.2
- Dry cleaning: Cleaning designed or intended for equipment in which the products held or contained are not at risk of contamination after production runs. Products are usually non-hygroscopic and non-sticky. In general, dry cleaning can be an option for products with a water activity below 60%.3 Examples of dry cleaning include brushing, aspiration (vacuuming) and magnetic separation.
- Wet cleaning: Cleaning in which water is used. Water can be used as a solvent to prepare sanitizing solutions.
- Cleanable: Refers to equipment designed to be easily freed from dirt and other contaminants.
- Crevice: Sharp, cleft-like, irregular opening of small depth that adversely affects cleanability.6
- Readily accessible: Location that can be reached by an employee from the floor, a platform, or other permanent work area.6
- Readily removable: Refers to equipment components designed to be easily separated from the machine with or without the use of simple hand tools.6
- Seal: Closure of an aperture so as to effectively prevent the entry or passage of unwanted matter (e.g., gaskets).6
- Self-draining: A condition resulting from a combination of design, construction, installation, and surface finish to prevent the retention of liquid except for normal surface wetting.6
Recommendations when designing and buying new bakery processing equipment
- Members of the bakery staff should have access to the technical specifications (e.g., data sheets) of equipment, specially when buying new assets. These documents should always be provided by the supplier or manufacturer of the equipment.
- Some particulate processing and handling equipment (e.g., flour storage bins, pneumatic conveyor systems, continuous mixers) should only be dry-cleaned. Equipment that processes and handles liquid products (e.g., milk and juice processing) require strict wet cleaning (COP/CIP) procedures to prevent microbiological contamination.
- Certain components of continuous dough mixing units (e.g., centrifugal and axial-flow pumps) can be cleaned in place by using cleaning solutions and rinse cycles.
- It is essential to make equipment manufacturers aware of the cleaning and food safety issues that the bakery has faced during normal operation. This allows for upgrading and improving the standard design of equipment.
- In some cases, bakeries can try to customize food processing equipment to meet hygienic expectations (e.g., by providing specifications to equipment suppliers regarding the design, construction, and installation of equipment).
- The European Hygienic Engineering and Design Group (EHEDG). EHEDG Document No. 8 “Hygienic Equipment Design Criteria.” 2nd ed., 2004.
- Baking Industry Sanitation Standards Committee (BISSC). Design Handbook for Easily Cleanable Equipment, 3rd ed., 2004, pp. 1–10.
- Murray, A. N. “Hygienic Design of Equipment.” Encyclopedia of Food Safety, vol. 4, Academic Press, Elsevier, Inc., 2014, p. 188.
- Lelieveld, H., Holah, J., and Gabric, D. “Cleaning of Surfaces.” Handbook of Hygiene Control in the Food Industry, 2nd ed., Woodhead Publishing, Elsevier Ltd., 2016, pp. 456–457.
- Stanga, M. “CIP (Cleaning in Place).” Sanitation: Cleaning and Disinfection in the Food Industry, 2nd ed., WILEY-VCH Verlag GmbH & Co., 2010, pp. 301–302.
- International Organization for Standardization (ISO). International Standard 14159 “Safety of Machinery – Hygiene Requirements for the Design of Machinery.” 1st ed., 2002, pp. 1–8.