KENYA STANDARD      DKS2861:2018  
ICS 67.080.20  
  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
   Production and handling of sweetpotato -   
code of practice  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
© KEBS 20 18       First Edition 20 18 
 
 
  DKS2861:2018  
ii  © KEBS 20 18 — All rights reserve d  
TECHNICAL COMMITTEE REPRESENTATION  
 
The following organizations were represented on the Technical Committee:  
 
University of Nairobi -Department of Food Science, Nutrition and Technology  
Agriculture and Food Authority - Food Cop directorate  
Kenya Agricultural & Livestock Research Organization  
Kenya  Industrial Research & Development Institute  
National Potato Council of Kenya  
Propack Ltd.  
Graduate Africa Ltd  
Food Science and Technology platform of Kenya  
International Potato Council  
Kenya Bureau of Standards — Secretariat  
 
 
 
 
 
 
REVISION OF KENYA STANDARDS  
 
In order to keep abreast of progress in industry, Kenya Standards shall be regularly reviewed. Suggestions for 
improvements to published standards, addressed to the Managing Director, Kenya Bureau of Standards, are 
welcome.  
 
 
 
 
 
 
 
 
 
 
 
© Kenya Bureau of Standards, 2018  
  
Copyright. Users are reminded that by virtue of Section 25 of the Copyright Act, Cap. 12 of 2001  of the Laws of Kenya, copyr ight subsists 
in all Kenya Standards and except as provided under Section 26 of this Act, no Kenya Standard produced by Kenya Bureau of Standards 
may be reproduced, stored in a retrieval system in any form or transmitted by any means without prior permission in writing f rom the 
Managing Director . 
 
 
 
   KENYA STANDARD       DKS2861:2018  
ICS 67.080.20  
© KEBS 20 18 — All rights reserve d  iii  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Production  and handling of sweetpotato - 
Code of practice  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
KENYA BUREAU OF STANDARDS (KEBS)  
 
Head Office:  P.O. Box 54974, Nairobi -00200, Tel.: (+254 020) 605490, 602350, Fax: (+254 020)  604031  
E-Mail: info@kebs.org,  Web:http://www.kebs.org   
 
Coast Region     Lake Region          Rift Valley Region  
P.O. Box 99376, Mombasa -80100   P.O. Box 2949, Kisumu -40100        P.O. Box 2138, Nakuru -20100  
Tel.: (+254  041) 229563, 230939/40  Tel.: (+254 057) 23549, 22396        Tel.: (+254 051) 210553, 210555  
Fax: (+254  041) 229 448 Fax: (+254 057) 21814  
 
 
  DKS2861:2018  
iv  © KEBS 20 18 — All rights reserve d  
Foreword  
 
This Kenya Standard has been developed by the  Tubers  and Tuber Products  Technical Committee under the 
guidance of the Standards Projects Committee and  it is in accordance with the procedures of the Kenya Bureau 
of Standards.       
 
 
The development of this standard was  in response to the need to accommodate the emerging quality, 
technological and environmental issues in the sector. The implementation of the standard is aimed at creating 
sector harmony, quality uniformity and fair trade in the sector, thereby creating va lue for the stakeholders. In 
the development of this standard it was envisaged that the current paradigm of sustainable development shall 
be ensured in the context of social, economic and environmental concerns. The standard thus intends to 
safeguard the i nterests of the stakeholders in the entire value chain, guarantee product quality and enhanced 
safety of the consumers.  
 
In the development of this standard, reference was made to the following documents:  
 
Recommended International Code of Practice General  Principles of Food Hygiene.  
 
EuroGap Protocol for Fresh Fruit and Vegetables _Sept_2001_Rev.02.  
 
Global Good Agricultural Practices  
 
 Acknowledgement is hereby made for the assistance derived from these sources.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
   KENYA STANDARD        DKS2861:2018  
 
 
© KEBS 20 18 — All rights reserve d  1  
Production and handling of sweetpotato — Code of practice  
 
 
1 Scope  
 
This Kenya Code of practice provides recommended Good Agricultural Practices for the production, post -
harvest handling, storage, packaging and transportation of fresh sweetpotato es ( Ipomea batatas ), intended 
for human consumption.  
 
2 Normative references  
 
The following documents are referred to in the text in such a way that some or all of their content constitutes 
requirements of this document.  For dated references, only the edition cited applies.  For undated references, 
the latest edition of the referen ced document (in cluding any amendments) applies:  
 
EAS 38,  General standard for the labelling of pre -packaged foods  
 
EAS 39, Hygiene in the food and drink manufacturing industr y — Code  of practice  
 
CAC/RCP 53, Code of hygienic practice for fresh fruits and vegetables  
 
CAC/RCP 44, Code  of Practice for Packaging and Transport of Fresh Fruits and Vegetables   
 
KS 2783  Warehousing and storage of roots and tubers - Code of practice  
 
3 Terms and definitions  
For the purposes of this Code of practice, the following terms and definitions shall apply:  
3.1 
fresh sweetpotato  
produce of species Ipomea batatas  grown for its roots  primarily used for human consumption  
3.2 
agricultural inputs  
any incoming  material (e.g. water, agricultural chemicals and planting material) us ed for the primary  
production of fresh  sweetpotato . 
3.3 
biological control  
use of competing biological agents (such as insects, micro -organisms and/or microbial metabolites) for the  
control of pests, plant pathogens and spoilage organisms  DKS2861:2018  
2   © KEBS 20 18 — All rights reserve d 3.4 
primary deterioration  
reduction in quality as a result of physiological changes characterized  by vascular streaking or vascular  
discoloration  
3.5 
secondary deterioration  
reduction in quality induced  by micro -organisms that cause rotting under aerobic and anaerobic conditions  
3.6 
curing  
operation of self -healing of wounds, cuts and bruises  
3.7 
clamp  
rectangular depression in the field where sweetpotato roots  are stacked and covered with straw/hay and soil to  
act as temporary storage  
 
4 Primary production and handling of fresh sweet potato  
4.1 General requirements  
Fresh sweetpotato  is grown and harvested under a wide range of climatic and diverse geographical  
conditions, using various agricultural inputs  and technologies. Biological, chemical and physical hazards may  
vary significantly from one type of production to another.  
In each primary production area, it is necessary to consider particular agricultural practices that promote  
production of safe fresh  sweetpotato es, taking into account the conditions specific to the primary production  
area, varieties of fresh sweetpotato  and methods used.  
During production, primary and secondary deterioration should be avoided so as to maintain the quality of  
fresh sweetpotato . Procedures associated with primary production shall be conducted under good hygienic  
conditions to minimize potential hazards to health due to the contamination of fresh sweetpotato  in 
accordance with EAS 39 and CAC/RCP 53.  
4.2 Agricultural in put requirements  
4.2.1  Inputs used for the production of fresh sweetpotato  shall conform to the relevant  
Standards.   DKS2861:2018  
© KEBS 20 18 — All rights reserve d  3 4.2.2  Agricultural inputs shall not contain microbial or chemical contaminants at levels that may adversely  
affect the safety and quality of fresh sweetpotato es. 
4.2.3  Growers shall use only agricultural inputs which are approved by the Competent Authority for the  
cultivation of  sweetpotato  and shall use them according to the product label for the intended purpose.  
4.2.4  The disposal of surplus chemical s and used containers shall be in accordance to the national  
environment regulatory agency guidelines.  
4.2.5 Agricultural workers who apply agricultural chemicals shall be trained  on proper application  
procedures.  
 4.2.6  Untreated Sewage and industrial waste shall not be used in sweetpotato production.  
4.2.7  Growers shall keep records of agricultural chemical applications. Records should include information  
on the date of application, the chemical used, the crop sprayed, the  pest or disease against which it was  
used, the concentration, method and frequency of application, and records on harvesting to verify that the  
time between applications and harvesting is appropriate.  
4.2.8  Agricultural implements and equipment shall be c alibrated, as necessary, to control the accuracy of  
application.  
4.2.9  Agricultural chemicals shall be kept in their original containers, labelled with the name of the  
chemical and the instructions for application and use  
 
.4.3 Handling during production  
During the primary production and post -harvest activities, effective measures shall be taken to prevent  
contamination of fresh sweet potato from agricultural inputs or personnel who come directly or indirectly into  
contact with fresh sweet potato.  
 
4.4 Handl ing during harvesting  
4.4.1  sweetp otatoes should be harvested when fully mature. Maturity can be assessed by:  
a) cutting fresh sweetpotato  in the field and observing the colour of the latex exuded; latex from  
immature sweet potato turns black, while from mature roots  remains creamy -white;  
b) rubbing the skin of the roots ; immature roots  skin easily peel off.  
 
 DKS2861:2018  
4   © KEBS 20 18 — All rights reserve d 4.4.2  Careful harvesting and proper handling of sweetpotato  is an important step towards successful  
storage.  
4.4.3  Sweetpotato can be harvested manually or mechanically. Care should be taken during the harvesting  
process to minimize damage such as bruising, scrapping or breaking of the sweet potato, to minimize postharvest  
losses.  
4.4.3  Care should be taken to prevent excessive damage and injuries during cleaning of harvested roots .  
4.4.4  Whether harvested manually or mechanically, the produce shall be carefully handled and  
transported to the packing facility immediately.  
To prevent conta mination, fresh sweetpotato  growers, harvesters and handlers shall adhere to the following:  
        a) fresh sweetpotato  unfit for human consumption shall be segregated during harvesting. Those which  
             cannot be made safe by further processing s hould be disposed of properly;  
        b) agricultural workers should not use harvesting containers for other purposes. Where  such containers 
have to be used for other purposes they shall be cleaned and     sanitized;  
         c) care shall be taken when harvesting fresh  sweetpotato  in the field to avoid exposure to contamination  
               with animal/human filth.  
        d)  only potable shall be used water for cleaning of the sweetpotato roots  
 
5 Storage and preservation  
5.1 General  
5.1.1 Fresh sweet potato  roots are perishable and under normal conditions , they store  for 3 to 4 weeks  while 
bruised  ones deteriorate more  rapidly .  
5.1.2 The  main causes of  post-harvest  losses  in sweetpotato are associated  
with mechanical damage, physiological condition (maturity, respiration, water loss), diseases and pests. To  
ensure effective storage of root  crops, these major causative factors need to be properly understood and,  
where appropriate, be properly controlled, taking into account the socio -economi c factors which prevail in the  
areas of production and marketing.  
 
5.1.2 General storage requirements  
5.1.2.1  For proper storage of sweetpotato  roots  ensure  that roots  with excessive mechanical injury and those    
damaged by insects or fungus are isolated   DKS2861:2018  
© KEBS 20 18 — All rights reserve d  5 5.1.2.2  Ensure the Storage structure p rovides adequate ventilation to avoid dampness and control temperature. 
Higher temperatures reduce the duration of storage by encouraging development of sprouts more so at high 
humidity and internal cork where viral disease is present.  
5.1.2.3  The recommended range of storage temperature and relative humidity for sweetpotato is 12-15 oC/80-  
95% rh. These conditions will guarantee storage up to 4 -6 months.  
5.1.2.4  At a temperature of 4oC-chilling injury and other del eterious effects such as:  
• increased susceptibility to infection by rot -causing organisms  
• internal discoloration and root break down and  
• reduction of ‘seed’ value of roots  due to failure to p roduce any sprouts when bedded are likely to occur  
5.1.2.4  Where  warehouse is used for storage of sweetpotato the structure shall comply with the requirements of 
KS 2783 . 
5.2 Preparing fresh sweetpotato  for storage  
Fresh sweetpotato es should be harvested and handled with care to minimize deterioration during storage  
and the following should be adhered to:  
a) retain only those roots  that do not show signs of injury. Roots  that are to be kept for more than one  
      week or more should be carefully selected since curing will not be effective on roots  with extensive  
      damage;  
b) establish curing of the roots  after harvest as a routine operation with, as far as possible,  
      minimum handling  
c) Severely damaged roots  should not be stored because of the following reasons:  
      a) lower quality;  
       b) increased risk of subsequent pathogenic losses; and  
        c) risk of introducing disease  causing organisms  into sound produce.  
 
5.3 Control of damage  
Mechanically damaged roots  will normally deteriorate rapidly and should not be stored and exported.  
Mechanical dam age can occur during all handling operations, particularly during harvesting and washing and  
damaged regions are more susceptible to microbial infection.  
Careful handling should be done during all handling operations and adequate drying and curing should b e 
ensured prior to packing and storage.  
 DKS2861:2018  
6   © KEBS 20 18 — All rights reserve d 5.4 Temperature control  
Temperature has a great influence on many factors that cause loss during storage; it influences the rate of  
sprout growth, the development of rotting micro -organisms and insect infestation. S torage at temperature  
below 10 °C will result in sweetening  and chilling injury  while storage temperatures above 25 °C will result in  
increased rate of decay  ,water loss and sprouting.  
Fresh sweetpotato  may be stored at 1 2 °C — 15°C   
Temperature control methods should aim at slowing down rates of physiological and microbiological  
deterioration.  
5.5 Curing of fresh sweetpotato  
5.5.1  Fresh sweetpotato  shall be properly cured as soon as possible after harvest to promote the formation of a  
hard cork layer. Curing should be carried out near the place where the roots  will be stored to minimize  
handling after curing.  
5.5.2  Curing of sweetpotato roots involves  holding roots at specific temperature an d relative humidity in order to  
 
i. Facilitate h ealing of injuries (cuts and bruises) incurred during harvest ing  and handling  
ii. Guarantee successful storage.  
iii. Prevent attack on the roots by rot -causing organisms and other pests.  
iv. Prevent excessive shrinkage while starches are being converted to sugars and  other 
flavor compounds during storage  
5.5.3  For proper curing:  
a) Do not wash roots since it interferes with wound healing process.  
b) Dry freshly harvested roots (if wet) in the sun for few hours before moving to curing room.  
c) Allow sufficient exchange of air  to avoid accumulation of Carbon dioxide.  
5.5.4  The recommended curing  conditions  are as shown in table 1:  
           Table 1: The recommended curing conditions for sweetpotatoes  
Relative humidity  Temperature  Number of days  
85% - 95%.  29 oC -32oC 2- 7   
85% - 95%.  27 oC 8-10  
85% - 95%.  24 oC 15-20 DKS2861:2018  
© KEBS 20 18 — All rights reserve d  7  
 
 
• NOTE 1: Higher temp >32oC will facilitate sprouting while lower temp -increase days of curing . At 2oC 
and below, there will be no more wound healing.  
• NOTE 2: Slow wound healing increases rate of infection by decay -producing organisms.  
 
5.6 Storage methods  
5.6.1 Storage in the soil before harvest  
Fresh sweetpotato  may be stored by leaving them un -harvested for short periods before the optimum harvest  
age. Roots  should not be left in the ground as a method of storage beyond the optimum harvest period  
because of the danger of roots  being infested by pathogens and any other physiological deterioration.  
 
5.6.2 Storage pits/heaps  
Storage in outdoor pits/heaps is not recommended.   Where used care  should be taken to reduce  dampness in 
order to prevent decay.  
 
5.6.3 Storing fresh sweetpotato  in crates/ baskets/boxes  
Freshly harvested sweet potato roots  can be stored in wooden cra tes or baskets. The crates should  be lined with 
a layer of sawdust, wood shavings, peat or any other suitable adsorbent materials. The spaces between the  
roots  should  also be filled with sawdust. Finally, the roots  are then covered with sawdust.  
To prevent the roots  drying out too early, the crate s should be lined with plastic foil. The sawdust should  
neither be damp nor wet. If the sawdust is too dry the roots  will deteriorate quickly. Sawdust which is too  
moist promotes the formation of mould and rot.  
The crates or baskets can simultaneo usly be used as containers during transport ation  (also several times) which  
saves on handling costs and also reduces injury to the roots  during transport.  
5.6.4 The field clamp  
Fresh sweetpotato  may be kept in a clamp (preferably under shade) for up  to eig ht weeks. The clamp should  
be in a well -drained location. Temperatures inside a ventilated clamp - should be approximately those of the  
ambient temperatures.  
 85% - 95%.  21 oC 25-30 DKS2861:2018  
8   © KEBS 20 18 — All rights reserve d 5.6.5 Other methods  
Other methods of storage and preservation include refrigeration, waxing of the roots  , modified atmosphere and 
chemical treatment.  
5.6.5.1 Refrigeration  
Reduced temperatures extend the storage ability of sweetpotato  roots  by delaying the rot processes which  
occur rapidly at normal storage temperatures. The most favourable temperature for the storage of fresh sweet  
potato is 12 °C — 15  °C  
 
5.6.5.2 Waxing  
 Sweetp otato roots may be preserved during storage  by coating them with food grade wax. The wax may or may 
not be  supported with a fungicide.  
 
6 Sorting and packing for export  
With suitable handling and storage, fresh sweetpotato  can be successfully transported for long distances  
including export by sea -shipment. Fresh sweetpotato  may be graded in terms of size and shape, with only  
one type being packed in one carton e.g. small rounded, small elongated, medium round etc.  
The optimum handling system is as follows:  
a) fresh sweet potato shall be carefully cleaned and dipped  in a solution of 0.05% Thiabendazole for  
15 - 30 s.  
b) after washing and fungicide treatment, the fresh sweet potato should be left overnight in a well  
ventilated area to dry before packing for dispatch . 
c) during shipment, the required storage temperatur e is 1 2 °C –15 °C.  
 
7 Packaging and labelling  
7.1 packaging shall  be done in accordance to the requirements of CAC/RCP 44  
 
7.2 Sweetpotato roots shall  be packaged in food grade materials that will safeguard the hygienic, nutritional and  
organoleptic qualities of the product.  The packaging materials shall also comply with other national regulations.  
7.3 Packaging materials shall protect the produce and ease handling including accounting for quantity  
in the lot.  
7.4 The selection of suitable containers  for commercial scale marketing requires very careful  DKS2861:2018  
© KEBS 20 18 — All rights reserve d  9 consideration. The following factors should be considered in choosing packaging materials:  
a) the level of losses occurring during marketing;  
b) the comparative cost of the present and improved packaging;  
c) the regularity of supply of the packaging material; and  
d) the acceptance of the packaging method to the market.  
 
7.5 Among the various types of packaging material that are available, the following are used;  
a) natural and synthetic fibre sac ks; 
b) moulded plastic boxes;  
c) sawn wooden boxes;  
d) cardboard boxes; and  
e) paper or plastic  film sacks.  
7.6 The net weight shall be:  
a) in metric units; and  
b) not more than 50 kg in line with ILO guidelines.  
NOTE : For sea-shipment, an additional 5% packing weight may be required due to weight loss which will occur 
during storage and  shipment.  
7.7 The labelling of packaged fresh sweetpotato  shall be in accordance with EAS 38 . 
8 Criteria for conformity  
A lot shall be dec lared as acceptable if the production and handling processes conform to the provisions of  
this Code of practice.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 DKS2861:2018  
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