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Pasteur, Lister and Cullen

Date Added: 12/10/2016

Blog: By Richard Elsdon, Technical Consultant, United Oilseeds

It recently occurred to me what a huge debt of gratitude we owe to Pasteur and Lister and as I wondered where on earth would we be if they had not made their discoveries. Pasteur (1822-1895) initially discovered what microbes “did” and more particularly, how they are responsible for spoiling food.  Pasteur then went on to develop vaccines, in particular one for Anthrax.

Lister (1827-1912) then took Pasteur’s work into the area of surgery which, at the start of his medical career, could only be described as “murder by surgery.” I say this, as the standards of hygiene at the time were truly diabolical and led to patient infections which could not be cured. The fatality rates were eye-watering.  Lister was the first to insist on the highest standards of hygiene in his operating theatres and wards, deploying 5% solutions of carbolic acid, with the result that infections and fatality rates were reduced dramatically.

Where does refrigeration come in? Actually a little before both Pasteur and Lister but in those early days it was a very “slow burn.”  William Cullen, a Professor at the Edinburgh Medical School designed a small refrigerating machine in1755, involving the boiling of diethyl ether in a partial vacuum. The experiment produced a small amount of ice but had no practical use at the time. In 1758, Benjamin Franklin and John Hadley collaborated on a project to investigate the effect of evaporation of a volatile liquid and managed to produce temperatures as low as -14C. But it took the need to transport beef from Texas in the mid 1870s before commercial refrigeration was developed and applied.


Pasteur, Lister and Cullen

So, where do these three seemingly unrelated discoveries lead? Let me take you to the storage of oilseed rape, where all will be revealed.

Although the incidence has been decreasing, we occasionally find ourselves in the unenviable situation of having to contact growers to tell them that the oilseed rape they have produced has either an ‘off smell’ or is rancid, mouldy or has mites. In almost every case, the cause can be traced back to the grower either not having been able to clean the store as well as he would have liked or not being able to keep the crop cool either before or after drying.  The consequences therefore are   invariably due to a failure to apply the principles of Pasteur, Lister, or Professor Cullen. The conversation with the grower in such cases invariably seeks to identify answers to the following questions:

-   Were you able to completely empty and then clean the store pre-harvest? (Some growers now
    pressure wash the store well before harvest). Thus removing as many microbes and insects as
    possible.

-   Was the newly harvested crop either dried and then cooled or, if immediate drying was not
    possible, was the new crop cooled?

-   Once the crop was deemed to be dry (8% moisture content or less, but above 6%) was the crop
     cooled by low volume ventilation AND the store temperature monitored?

Now this last point can be the source of some misunderstanding.  Cooling involves low volume aeration (about 12 cubic feet of air per minute per tonne). In addition, there only needs to be a temperature difference of 3 deg C between the stack temperature and the temperature outside. This monitoring is best done automatically with a differential thermostat. I have heard some growers say “I haven’t blown the crop as the night time temperature hasn’t been low enough.” (At some point in the night it will have been - but who wants to get up in the middle of the night to switch a fan on?)  By cooling the crop you are rapidly reducing the activity of any in-store insects and once the temperature is low enough, they either die or virtually cease all activity.

With everyone on the farm doing much more than they did a few years ago, it is very tempting to cut corners. The work of Messrs Pasteur, Lister and Cullen, prove that it is very unwise to do so.  “Best practice” is your best friend.

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