Food manufacturers face an array of options when considering new processing vessels for their operation, as several design styles can be used to cook, cool and mix their products. This guide can help you match vessel design to the characteristics of your product and operation to identify the right style for process quality, efficiency and safety. 


Factors about your product that affect vessel design decisions

Several factors about your product must be considered to determine the best vessel solution for your operation. These include:

  • Product weight and viscosity

Heavy and thick products flow through your vessel much differently than lighter and low-viscosity products. Decisions on vessel configuration and agitation styles will affect mixing performance, ease of discharge and cleaning. In applications with cut vegetables, fruit or other solid ingredients, multiple smaller capacity vessels may better ensure product integrity than a single large capacity vessel, as they can avoid crushing or damaging the ingredients with excessive weight. In the case of a high-viscosity product, the bottom shape of the vessel can be designed to promote easier discharge with the appropriate configuration and agitation.

  • Ingredient characteristics

The characteristics of your product’s ingredients affect your vessel design choices due to their impact on cooking and mixing. Delicate ingredients such as tomatoes or fruits, or those intended to remain solid throughout the cooking and mixing process, may require a gentler cooking and mixing environment than those that will be emulsified. Ingredients that can caramelize may need different heating and cooling configurations to avoid product burn-on and maintain quality.

  • Product variety and variability

If you produce only one product, your vessel’s design can be completely customized around it. But if you are a contract manufacturer or otherwise produce multiple products, your vessel must be more flexible. You may need a vessel that can perform well for a variety of product weights and viscosities, or one that can accommodate a wide range of heating and cooling settings. Also, a configuration that accelerates cleaning and product turnaround becomes even more vital for operations that produce multiple products.


Factors about your operation that affect vessel design decisions

Beyond your product’s characteristics, consider these factors about your processes, business objectives and physical facility to determine your best vessel solution option:

  • Production volume

Your throughput objectives will influence your vessel capacity, and therefore your vessel style. Capacity choices must also reflect any physical space limitations, your workflow processes and personnel required.

  • Scalability

Your future growth plans must also be considered in vessel design to ensure your equipment can scale with your needs. Factoring in this anticipated growth upfront may influence choices for capacity, mixing system, heating and cooling configuration and product discharge, and prevent costly revisions later.

  • Physical space and mechanical requirements

Any mechanical limitations you have (e.g., access to heat source) or physical space constraints must be considered in your vessel design. This includes space above and below the vessel to ensure room for product fill and discharge, as well as efficient access for cleaning.  

  • Integrated processes and equipment

Unless they are part of an operational overhaul or new line, your new vessels must work within your existing production processes and the boundaries of other equipment.


Processing vessel options:  matching the design to your need

Once you have a grasp of your product and operational factors, you can begin to apply them to a range of vessel design options to determine the best solution for your situation: 


Hemispherical Kettles

Hemispherical kettles

Image by Lee Industries


Hemispherical kettles are suited for applications where consistent ingredient blending and mixing are required. The kettle’s bowl-like bottom shape provides the ideal profile to accommodate all styles of agitation, including inclined scraped surface agitators, to consistently blend a wide variety of ingredients and viscosities. This makes it useful for food processing applications where delicate, solid ingredients, such as cooked vegetables or fruit, must be gently mixed during the cooking process. The hemispherical shape also makes it possible for scrape surface blades to access 100% of the heat transfer area, which aids in maximum discharge of the batch.


Key Design Features

  • Enables full vessel access for mixing and 100% scraping
  • Super jacket with large annular space on the hemisphere to accommodate steam or water for heating and cooling
  • Can accommodate all styles of agitation, including inclined agitation
  • Capacity up to 2,500 gallons for most agitation; 1,000 gallons for inclined agitation
  • Maximum drainage for high yields

Ideal Application

  • Critical mixing products (e.g., delicate ingredients, hard-to-mix ingredients)
  • Multiple product applications
  • High-viscosity applications
  • High-pressure or reaction applications

Dished-Bottom Tank

dished-bottom tankImage by Lee Industries


A dished-bottom tank, featuring a gently sloping circular bottom, provides mixing capabilities and performance that are close to those of a hemispherical kettle. While its design does not enable the benefits of an inclined agitator like a hemispherical kettle, the rounded bottom assists in discharging product from the tank and provides better suspension of solids than a cone bottom. Moreover, like all tanks, its height does not have to remain proportional to the bottom—as it must with a hemispherical kettle—which means it can be designed to accommodate larger capacities. 


Key Design Features

  • Capacity up to 6,000 gallons
  • Heat transfer jacket options include uniflow coil, standard or dimple

Ideal Application

  • Large capacity high viscosity production where mixing is critical
  • Large capacity, high pressure or reaction applications


Cone-Bottom Tank

Cone-bottom tanksImage by Lee Industries


Cone-bottom tanks, with their circular cone-shaped bottom profile, are more suited to be used as hold tanks which require agitation for keeping a product suspended while waiting to be pumped to the filler. Increasing the angle of the cone bottom can improve the flow of materials to the discharge outlet at the bottom of the tank.

While its mixing capabilities are superior compared to either flat- or pitched-bottom tanks, there are mixing limitations with cone-bottom tanks, primarily regarding suspension of solids or mixing high viscosity products. Since an agitator cannot reach fully to the bottom of the cone, the tank’s geometry leads to accumulation of unmixed material at the very bottom, especially when the cone bottom angle has been made steeper to facilitate product discharge. This limitation can sometimes be overcome by designing a non-scraping fin or baffle at the very bottom of the agitator to provide more complete mixing.


Key Design Features

  • Capacity up to 6,000 gallons
  • Standard 120 degree included angle, can be customized to 60 degree


Ideal Application

  • Very high viscosity or semi-solid product
  • Hold tank

Pitched-Bottom Tank

Pitched-bottom vesselsImage by Lee Industries


Pitched-bottom vessels feature a flat bottom that is angled lower to one side of the tank to provide a drainage path to the bottom of the vessel. A discharge valve can be placed at the lowest side of the vessel bottom, making it easier to operate the valve from the side of, instead of underneath, the vessel. While a pitched-bottom vessel provides for better drainage and more complete product discharge compared to a flat-bottom vessel, agitation can still be problematic, since there will always be a gap at the bottom of the vessel that is out of reach of the agitator blades. Unmixed materials can accumulate in this gap, which can block the discharge outlet and allow unmixed ingredients to flow into the batch upon discharge. For this reason, pitched-bottom tanks are suitable for low-viscosity products with no solid content.


Key Design Features

  • Sidewall discharge for environments with limited room for under-tank piping

Ideal Application

  • Water-like low viscosity with or without heat transfer


Flat-Bottom Tank

Flat-bottom tanksImage by Lee Industries


Flat-bottom tanks are the most basic tank configuration and are commonly used for storage and holding of liquid process materials. While a flat bottom tank profile limits any mixing application, these tanks can be paired with a bottom-sweep or propeller mixer for mixing lower-viscosity materials.

Product discharge can also be problematic in a flat bottom tank because these tanks do not have the angled discharge path available with other tank bottom profiles. This may lead to incomplete drainage of product from the batch and make the vessel more difficult to clean. For these reasons, flat-bottom tanks are not widely used for processing applications where mixing is required.


Key Design Features

  • 10,000+ gallon capacity 

Ideal Application

  • Product storage with limited mixing needs

Beyond matching the vessel design to your needs, your vessel can be configured with an array of options and accessories to further enhance your operation. Depending on your product and business goals, these can include instrumentation, jacket type, covers, custom finishes, tilting kettles, nozzle types and customizable operator safety features. 

Choosing your vessel design is a critical step for your operation. Whether you are in start-up, replacement or expansion mode, the more you understand how to match your design to your product attributes and operational characteristics the higher the return on your vessel investment will be.