andrew murray consulting

food process and project engineers
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Ecological Thermodynamics -

What is it and why is it vital to the future of the food industry.

G. Tyler Miller, an American Chemist calculated that -
Three hundred trout are needed to support one man for a year. The trout, in turn, must consume 90,000 frogs, which must consume 27 million grasshoppers that live off 1,000 tons of grass.

Does this mean that if trout was the only available food to man one man would require the input of 1000 tons of grass every year? And what has it to do with Thermodynamics?

What is it?

Let us consider a simple idealistic ecological system containing only grass, rabbits and foxes.  We might want to know:

    * how efficient  the grass is at converting inorganic matter into rabbit food

    * how efficient is the rabbits' production of fox food

    * how efficient are the foxes in producing biomass and energy from rabbits.

To answer the questions meaningfully and a host of similar ones we need to understand the basics of the thermodynamics of the systems.

The laws of thermodynamics can be adapted for simplicity to state the following

All work and growth requires energy and  energy cannot be created or destroyed; (First law). That is, without photosynthesis and radiation from the sun there will be no grass, no rabbits and no foxes.

 Increased order (growth, complexity) in one part of a system entails increased disorder (entropy) in another part (Second law) An increase in fox order implies an increase in rabbit disorder.

 Mass cycles through an eco-system. Thus in the system we considered above the mass goes from inorganic matter to grass to rabbit to fox and via decomposition and microbial action back to inorganic matter. We need to add the decomposers (bacteria) to our hypothetical system.  The relatively short times in our planet's history that the decomposers have been inactive have resulted in the deposits of fossil fuels which we are now depleting.

In contrast to mass, energy flows through the system.  It enters the system through the sun’s heat and light in photosynthesis and is eventually dissipated in heat generated through movement, metabolism, and decomposition and it is then radiated out through the atmosphere to space.

This is the basic principle of ecological thermodynamics and is true for the system planet earth - materials cycle in ecosystems, energy flows through them. The mass of the planet is fixed.  Radiant energy from the sun continually reaches us and energy is continually being dissipated from the planet into space.

 Ecosystems are far more complex than the simple grass-rabbit-fox scenario and one needs to consider food webs rather than food chains.

 Biomass can only be produced by plants and certain bacteria. We designate these autotrophs or primary producers.

 Herbivores convert the plant material into energy and biomass.  Carnivores in turn use the energy and mass provided by the herbivores.   Once again it is not quite so simple.  There are omnivores and there are higher levels of carnivores that prey on other carnivores.

 Each step is designated a trophic level.  Thus plants are the lowest trophic level, herbivores (eg grasshoppers) next and levels of carnivores (frogs, trout)  and omnivores (humans)  higher up the food chain or food web.  Finally bacteria take the waste from all these process and convert it back into inorganic matter.

In terms of the second law every conversion is characterised by a reduction in energy. It is possible to draw an energy pyramid which shows the energy produced by each trophic level. It is also possible to draw a pyramid of mass and a pyramid of numbers.

The American environmentalist, Howard T Odum studied an ecosystem at Silver Springs, Florida.  As a part of his study he constructed an energy flow diagram which gave the flow of energy per square metre per year.  This has been simplified to an energy pyramid.  Alongside the energy pyramid it is possible to construct pyramids of number, the census at a given time of the populations and a pyramid of mass, the standing mass of the system. The standing mass pyramids and the numbers pyramids may be inverted indicating that the lower trophic levels replenish more quickly than the level above. This is similar to the food in your larder at a given time being less than you require for the year.  You buy more when needed.  The pyramid of energy cannot in terms of the first law be inverted.

 Similar research has been conducted for other systems and indeed energy diagrams have be produced for the analysis of our total global footprint.

 And why does the industry need to take note

 The analysis of the energy flows can become rather complex and indeed particularly so when one considers human requirements and expectations.  An analysis of the planet might consider energy and entropy in transfers between the atmosphere, lithosphere, hydrosphere, biosphere and technosphere as well as within each of these divisions.  A few of the important results from many such analysis  are the following:

 There is a limit to the number of trophic levels that can be sustained in any food chain.

 The efficiency of each level may be considered as being about 10%. Some may be as low as 1% and some reach as high as 15%.  Generally animal husbandry will provide for more efficient systems.

The greenhouse gas emissions from the livestock industry is between 18% and 51% of the total global emissions (depending on how one does the calculations).  Thus, they possibly exceed the emissions from power plants world wide.   This information has led to a trend of eco-vegetarianism.

 Humans presently appropriate 40% of all terrestrial net prime production (NPP).  The bulk of this is for food.   It does not leave much space for bio-energy or to alleviate poverty without drastic changes to technology, reduction of waste and reduction in expectations.

 Responsible use of biomass and bio-energy in the future is central to human survival.  Technically, this is in the hands of the agricultural and food industries. A holistic approach will require understanding of how ecosystems use energy.


Hygienic design, PRPs and HACCP

The object of a food process operation is to produce safe wholesome food from specified raw materials.

This requires the design of a suitable process to kill or control relevant microorganisms together with a suitable process control system.

Further it requires the application of hygienic design incorporating:

            •         factory siting and construction
         design of the building structure
         selection of surface finishes
Cape Town  
         segregation of work areas to control hazards
         flow of raw materials and product
         movement and control of people
         design and installation of the process equipment
         design and installation of services 

and hygienic practises which include:

         practises that return the processing environment to its original condition. These are usually referred to as cleaning and disinfection or sanitation programmes.

         practices that keep the building and equipment in efficient operation. These are referred to as the maintenance programme.

         practices that relate to the control of cross-contamination during manufacture, usually related to people, surfaces, the air and the segregation of raw and cooked product. Such control is generally referred to as Good Manufacturing Practice (GMP).

Hygienic design and hygienic practices include almost all the listed PRPs. However there are others such as supplier control and recall programmes. These are added. 

A food safety management programme (HACCP) is  a surround that encompasses all these things.

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PRPs listed in SABS 10330

Hygienic Design
  • External areas to the facility
  • Building structure, ablution facilities, production,distribution and storage facilities
  • staff and product flow
  • construction of equipment
  • services needed for production, for example, air, water
Hygienic Practices
  • maintenance programme
  • cleaning and disinfection programme
  • pest control programme
  • refuse and waste control programme
  • personal hygiene programme
Other PRPs
  • product recall and traceability programme
  • control of suppliers
  • relevant training programmes
  • relevant records

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