LETTERS TO THE EDITOR
INCORPORATING COLD CHAIN
Continuing the conversation on
reducing post-harvest fruit losses
Jan Lievens, senior consultant applied post-harvest technologies at Umhwebo Trading Enterprise (UTE)
In digging a little deeper into the subject discussed in the January/February 2019 feature entitled
“Reducing post-harvest losses of fruit”, some interesting and important information was unearthed.
A
s stated in the original article,
effective cooling and good
cold chain management are
among the most common methods
used to control post-harvest ripening
and senescence of fruit and vegetables.
Worldwide, the fruit industry swears
by cooling as the primary means of
preserving fruit to avoid losses. Generally,
the industry believes this is true to a
certain extent. However, when looking at
this in detail, cold chain management is
far more than just keeping things at the
right temperature while being stored or
transported.
While researching post-harvest losses of
fruit, hundreds of papers were discovered,
along with guidelines, books, and rules
that are readily available on what to do in
theory, many of which are overlooked. All
the theory is brilliant and factual, and on
the surface, there is little or no difference
between it and practice. However, when
examined closely, in practice, there is much
more to understand and consider, thus
making theory a baseline rather than a full
procedure.
Reading through the information, it
became very clear that at no point was
the importance of applied post-harvest
technologies and the chain of events in the
process mentioned. After further research,
it was obvious that nature never breaks
her own rules, and that is exactly where far
more attention to detail is required.
final cooling. There are those that call this
‘post-harvest gynaecology’, or, simply
put, cutting the fruit from the tree or vine
is like cutting the umbilical cord from a
baby. Once this is done, you have to look
after the baby, or it dies. The same is true
for fruit.
The timing between harvest and getting
the fruit from the orchard to starting the
post-harvest process in pre-coolers is of
utmost significance. Getting the field heat
off in the appropriate manner and as soon
as possible, is paramount. At this point,
relative humidity and airborne bacteria
removal in the pre-coolers and pack
houses are crucial.
As stated, nature never breaks her
own rules; however, there are ways to
bend the rules to create a gap in what is
called the window of opportunity. This has
been quoted and proven by a number
of industry experts. Therefore, it seems to
be possible and viable to ‘trick’ nature for
an instant and improve the post-harvest
process. It became obvious that preserving
fruit quality after harvest comes through
smart understanding and leaving nothing
to chance.
THE IMPORTANCE OF AIRFLOW
NOT JUST ABOUT COOLING
Locally, fruit is being transported in open
trucks with no temperature control, causing
a break in the cold chain, and losses.
BOX AND PUNNET DESIGNS NEED
TO RESPECT AIRFLOW
All too often, cartons in the field are used
in a manner where properly cooling
airflow through them is impossible. Their
use does not even consider the inner
packaging. Further findings proved
beyond doubt that the way and the
timing of how the fruit is handled after
palletisation and before it arrives to the
forced air coolers, either on the farm or
transported to a central unit, is vital.
Proof was delivered and found on many
transportations of open trucks carrying non-
protected fruit pallets. The inter-stacking of
pallets of boxes from different farms and
different suppliers coming together in a
central cooling unit, is nearly always an
issue and cause of reduced fruit quality.
The post-harvest process is not just
about cooling but also about the timing
between harvest and the processes until
the product is in its carton and ready for
“Table grapes are non-climacteric fruit,
which means they do not continue to ripen
after harvest and for this reason they should
be harvested when they reach optimum
maturity. However, fruit quality tends to
deteriorate rapidly during postharvest
handling and storage, thus reducing
shelf-life during marketing. There are three
compelling reasons why table grapes should
be cooled promptly and thoroughly after
harvest to maintain quality: to minimise
water loss from fruit; to retard developments
of decay by fungi; and to reduce the rate of
respiration. Minimising water loss is probably
the most urgent reason for cooling. Like
many other fruit cooling systems, table
grape cooling is achieved by forcing cold
air through the ventilated package. Forced
air cooling technique has been discussed
by many researchers, but its application is
often not efficiently achieved, mainly due
to the resistance to airflow imposed by the
packaging container and the contents.”
Too many box designs, each with different
‘cooling’ pattern profiles and non-uniform
inner core temperatures, create havoc in
many central cooling tunnels.
DON’T BE FOOLED BY ‘FAST’
COOLING TIMES
Having all boxes with all fruit at the right
core temperature in the same cooling
sequence is important. Modern cooling
tunnel design with the latest airflow,
measuring, and variable speed drive (VSD)
technology, is virtually non-existent, not
implemented, or not considered important.
Through research, the ‘steri’ process’
is another area that must be carefully
considered, as operators often destroy
the fruit with exceptionally high wind
speeds for three to four days when
already on the correct temperature. This
causes unnecessary damage due to bad
early preparation after harvest, followed
by a far-too-low relative humidity through
perforated packaging at further high
wind speeds.
Container and truck loading with
accurate temperature and condition
control is another area of concern.
Attention to detail is required at this point
and this does not need to be repeated.
In conclusion, it is clear that post-harvest
management for better fruit is not all
about only cooling; it would be naive and
short-sighted to say so. After a rewarding
investigation that became an excellent
learning experience, it was noted that
practical, coordinated cooperation and
implementation on ground level with
industry specialists and organisations, are
necessary in the fruit farming industry. The
underlying reason for this is that South
African fruit deserves to arrive in the best
possible condition at the client, both locally
and overseas. CLA
In most fresh food refrigeration systems,
heat is transferred primarily by forced
convection. Here cold air is forced through
food packages and the temperature
and its homogeneity are governed by the
patterns of airflow in the cartons. There are
vast numbers of papers that discuss this
issue in detail; hence, the title of this article.
However, in the field and in practice,
what is discussed by many experts is not
happening on a homogeneous and
structured basis.
Taking an example in the table grape
industry from the article “Resistance to
airflow and cooling patterns through
multi-scale packaging of table grapes”
(published in the International Journal of
Refrigeration in March 2012):
It is important to ensure that box designs have the same ‘cooling’
pattern profiles and uniform inner core temperatures for the product.
The timing between harvest and getting the fruit from the orchard to
starting the post-harvest process in pre-coolers, is of utmost significance.
COLD LINK AFRICA • May 2019
www.coldlinkafrica.co.za
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