ICS 67.220.20                       DMS 1257:2023  
                Second edition  
 
 
 
 
DRAFT MALAWI STANDARD  
 
 
 
 
 
 
 
 
Baker’s yeast  – Specification  
 
 
 
 
 
 
 
 
NOTE: This is a draft proposal and it shall neither be used nor regarded as a Malawi Standard  
 
__________________  
 Published by  
MALAWI BUREAU OF STANDARDS BOARD   
  ICS 67.220.20         DMS 1257 :2023       
Second edition  
 
 
 
 
 
 
 
 
Baker’s yeast  – Specification  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Obtainable from the  
Malawi Bureau of Standards  
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P O Box 946  
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 i TABLE OF CONTENTS  
  
Contents                                                                                                                                                     page     
Foreword………………………… ………………………………………………………………………………… ……. ii 
Technical committee…………………… ……………………………………………………………………………… ..ii 
Notice…………………………………………………………………………………………………………………… ...ii 
Scope……………………………………………………………………………………………………………………..  1 
Normative references……………………………………………………………… ……………………………………  1 
Terms and definitions …………………………………………………………………………………………………… 1 
Types of yeast………………………………………………………………… …………………………………… …... 2 
Essential comp osition and quality factors …………………………………………… ……………………… ……….  2 
Hygiene ……………………… …………………………………………………………………………………... ..........  3 
Packakging and storage …………………………………………………………………………………… …………… 3 
Labelling……………………………………………... …………………… ..…………………………………………...  3 
Sampling and test methods ………………………………… …..….………………………………………………...  4 
Annex A ……………………………………………………………….... ……………… …….……………… ……… …. 5 
Annex B ……………………………………………………………. …..……………… ……. …………………………  6 
Annex C……..……… ….………………………………………………………………………………… ……………...7 
Annex D…………………………………………………………………………………………………………………..9  
Annex E …………… ……………………………………………..………………………………………………… .....10 
Annex F ………………… ….….……………………………………………………………………………………….12  
Annex G…………………………………… .…………………………………………………………………………..  16 
 
 
 
 
 
 
 
 
 
 
 
 
  
 ii FOREWORD  
 
This draft Malawi standard was prepared by MBS/TC 19, the Technical Committee on  Bread and confectioneries,  
to provide requirements  for baker’s yeast . It is the revision of MS 1257 :2016, Baker’s yeast  – Specification . 
 
In preparing this draft Malawi standard reference was made to the following standard:  
 
East African Standard, EAS 997:2019 , Baker’s yeast  – Specification . 
 
Acknowledgement is made for the use of the information.  
 
 
TECHNICAL COMMITTEE  
 
This draft Malawi standard was prepared by MBS/TC 19, the Technical Committee on Bread and confectioneries , 
and the following companies, organizations a nd institutions were consulted : 
 
Bakelines Limited ; 
 
Bakeman’s Confectioneries Limited ; 
 
Bakhresa Malawi ;  
 
Blantyre City Council ; 
 
Bread Talk ; 
 
Bvumbwe Agricultural Research Station ; 
 
Competition and Fair Trading Commission ; 
 
Consumers Association of Malawi ; 
 
H.M.S Food and Grains Limited ; 
 
International Potato Centre Malawi ; 
 
Kachere Bakery ; 
 
Lilongwe University of Agriculture and Natural Resources ; 
 
Malawi University of Business and Applied Sciences ; 
 
Mega Bakers ; 
 
Ministry of Health – Department of Nutrition, HIV and AIDS ; 
 
Ministry of Trade and Industry ; 
 
National Fortification Alliance ; 
 
Rab Proc essors ; 
 
Shoprite Trading Limited ; 
 
Tehilah Bakery ; 
 
University of Malawi ; and  
 
Universal Industries . 
 
 
 
 
NOTICE  
 
This standard shall be reviewed every five years, or earlier whenever it is necessary, in order to keep abreast of 
progress. Comments are welcome and shall be considered when the standard is being reviewed .1 
                                                                                                  DMS 1257 :2023  
DRAFT MALAWI STANDARD   
 
Baker’s yeast  – Specification  
 
 
1 SCOPE  
 
This draft Malawi standard specifies requirements, sampling and test methods for baker's yeast.   
 
 
2 NORMATIVE REFERENCES  
 
The following standards contain provisions which, through reference in this text, constitute provisions of this 
draft proposal. All standards are subject to revision and, since any reference to a standard is deemed to be a 
reference to the latest edition of the standard, parties to  agreements based on this draft Malawi standard  are 
enco uraged to take steps to ensure the use of the most recent editions of the standards indicated below. 
Information on currently valid national and international standards can be obtained from the Malawi Bureau of 
Standards.  
 
MS 19: Labelling of prepacked foo ds – General standard;  
 
MS 21: Food and food processing units – Code of hygienic conditions;  
 
MS 30:  Fortified wheat  flour – Specification ; 
 
CAC/GL 50: General guidelines on sampling ; 
 
ISO 4832; Microbiology of f ood and animal feeding stuffs – Horizontal method for the enumeration of Coliforms 
– Colony -count technique ; 
 
ISO 6579 -1: Microbiology of the food  chain – Horizontal method for the detection, enumeration and serotyping 
of Salmonella – Part 1: Detection of Salmonella spp;  
 
ISO/TS 6579 -2: Microbi ology of food and animal feed – Horizontal method for the detection, enumeration and  
serotyping  of salmonella – Part 2: Enumeration by a miniaturized most probable number technique ; 
 
ISO 6888 -1: Microbiology of f ood and animal feeding stuffs – Horizontal method for the enumeration of 
coagulase -positive staphylococci (Staphylococcus aureus and other species) – Part 1: Technique using Baird -
Parker agar medium ; 
 
ISO 6888 -2: Microbiology of f ood and animal feeding stuffs – Horizontal method for the enumeration of 
coagulase -positive staphylococci (Staphylococ cus aureus and other species) – Part 2: Technique using rabbit 
plasma fibrinogen agar medium ; 
 
ISO 6888 -3: Microbiology of f ood and animal feeding stuffs – Horizontal method for the enumeration of  
coagulase -positive staphylococci (Staphylococ cus aureus and other species) – Part 3: Detection and MPN 
technique for low numbers ; 
 
ISO 7251: Microbiology of f ood and animal feeding stuffs – Horizontal method for the detection and 
enumeration of  presumptiv e Escherichia coli – Most probable number technique ; and  
 
ISO 15914: Animal feeding stuffs – Enzymatic determination of total starch content . 
 
 
3 TERMS AND DEFINITIONS  
 
For the  purposes of this draft Malawi standard , the following te rms and definitions shall apply:  
 
3.1 
baker’s yeast  
cells of one or more strains of the yeast Saccharomyces cerevisiae  that aid the fermentation and aromatic 
activity of fermented doughs  
 
  
 2 3.2 
Fresh Baker’s Yeast (FBY)  
baker’s yeast consisting of living cells of Saccharomyces  cerevisiae  
 
3.3 
Dry Baker’s Yeast (DBY)  
baker’s yeast consisting of living but inactive cells of Saccharomyces cerevisiae  
 
 
4 TYPES OF BAKER’S YEAST  
 
Baker’s yeast shall be categorised in two types  as follows:  
 
4.1 Fresh Baker’s Yeast  (FBY)  
 
FBY may be in three major forms:  
 
4.1.1  Block or compressed yeast   
 
This shall be in the form of a block. The texture or consistency shall be either high plasticity (kneadable, 
deformation possible without breakage) or friable/crumbly (blocks easily broken in to small pieces).  
 
4.1.2  Granulated yeast  
 
This shall be in the form of small granules . 
 
4.1.3  Liquid yeast  
 
This shall be a liquid suspension of yeast cells in wat er with a cream -like viscosity.  
4.2 Dry Baker’s Yeast (DBY)  
DBY may be in the following forms : 
4.2.1  Active dry yeast  
 
Yeast that requires reactivation by rehydration using warm water (38 °C – 45 °C ) prior to use. It may be of 
spheroid particles , 0.2 – 3 mm in diameter.  
 
4.2.2 Instant dry yeast  
 
Yeast dried in a way that rehydration is not necessary to facilitate reactivation. It consist s of porous cylindrical 
yeast particles with an approximate diameter of 0.5 mm and length up to a few millimetres.  
 
 
5 ESSENTIAL COMPOSITION AND QUALITY  FACTORS  
 
5.1  General quality requirements  
 
Baker’s yeast shall:  
 
5.1.1  Be ivory in colour;  
 
5.1.2  Have an odour typical of yeast;  
 
5.1.3  Be free of extraneous materials;  
 
5.1.4  Not be slimy or mouldy; and  
 
5.1.5  Not show any signs of deterioration or decomposition.  
 
 
  
 3 5.2  Specific  compositional  requirements  
 
Baker’s yeast shall comply with the compositional requirements  given in Table 1  when tested in accordance 
with the test methods specified therein.  
 
Table 1 – Compositional  requirements for baker’s yeast  
 
S/N Characteristic  Requirement  Test 
method  Fresh baker’s yeast (FBY)  Dry baker’s yeast (DBY)  
1 Moisture, % (m/m), max  73 8 Annex A  
2 Edible starch, % (m/m), max  7 10 ISO 15914  
3 Dispersibility in water  No yeast cell deposits  No yeast cell deposits  Annex B  
4 Fermenting power , ml, min  1000  350 Annex C  
5 Dough -raising capacity  To satisfy the test  To satisfy the test  Annex D  
 
5.3 Microbiological limits  
 
Baker’s yeast shall comply with the microbial limits given in Table 2  when tested in accordance with the test 
methods specified therein.  
Table 2 – Microbiological limits for baker’s yeast  
 
S/N Characteristic  Maximum l imits  Test 
method  Fresh Baker’s Yeast 
(FBY)  Dry Baker’s Yeast 
(DBY)  
1 Coliform count , cfu/g  10 50 ISO 4832  
2 Escherichia coli , MPN/g  Absent  Absent  ISO 7251  
3 Salmonella  in 25 g  Absent  Absent  ISO 6579  
4 Staphylococcus aureus , cfu/g  10 10 ISO 6888  
5 Rope spore count, cfu/g  10 100 Annex E  
6 Bacterial flora, other than yeast, 
millions per gram (on dry basis)  0.75 8.0 Annex F  
 
 
6 HYGIENE  
 
Yeast shall be manufactured, packaged  and stored under hygienic conditions in premises conforming to the 
requirements  prescribed in MS 21.  
 
 
7 PACKAGING AND STORAGE  
 
7.1 Fresh Baker’s Yeast  
 
The FBY blocks shall be wrapped or packed in clean wax ed paper or any other suitable food grade wrapping 
material or non -toxic wrappers to preserve freshness and to prevent undue deterioration during storage.  
 
The yeast blocks shall be stored at the temperature s of between 1 to 60 C.  
 
7.2 Dry Baker’s Yeast  
 
The DBY shall be packed in clean, sound and suitable airtight  containers preferably tin containers such a 
manner as  to prevent the absorption of moisture and to prevent undue deterioration during storage.  
 
The yeast shall be stored in a cool and dry place at a te mperature of not more than 250 C. 
 
 
8 LABELLING  
 
In additio n to the labelling requirements stipulated in MS 19 , the packages shall be legibly and indelibly marked 
with the following information:  
  
 4 8.1 Name of the product shall be “Baker’s Yeast” . Type  of the product may be indicated in close proximity 
to the name of the product e.g. “Baker’s Yeast, Granula ted”, “Instant Baker’s Yeast”, “Granulated Baker’s 
Yeast” , etc. ;  
 
8.2 Name and physical address of the processor/packer/importer;  
 
8.3 Date of manufacture;  
 
8.4 Expiry date ; 
 
8.5 Batch or code number ; 
 
8.6 Net weight of the product in metric units;  
 
8.7 List of ingredients in descending order by quantity when used;  
 
8.8 Country of origin ; 
 
8.9 Storage instructions ; and  
 
9.0 Declaration 'Contains  edible starch', when edible starch is added.  
 
10 SAMPLING  AND TEST METHODS  
 
Representative samples shall be drawn in accordance to th e procedure outlined in Annex G  and tested using 
appropriate standard methods declared in this draft Malawi standard . 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 5  
Annex A  
(Normative)  
 
DETERMINATION OF MOISTURE  
A.1 APPARATUS  
A.1.1  Dish, with a cover , made of glass or aluminium, about 25 mm in diameter  
A.1.2  Glass stirring  rod, approximately 60 mm long, with a flattened end . 
 
A.2 REAGENT  
Alcohol, Ethyl alcohol or rectified spirit.  
 
A.3 PROCEDURE  
Weigh the dish with the cover and stirring rod ( M). Transfer to this, add about  10 g of dry yeast or 2.5 g of fresh 
yeast and weigh accurately to the nearest milligram (M 1). Remove the cover of the dish and add 5 ml of alcohol. 
Mix thoroughly using the stirring rod and leave the stirring rod in the weighing dish. Place the cov er on the dish 
and dry at 105 ± 1 °C for 4 h for fresh baker’s yeast and 6 h for dry baker’s yeast. Co ol the di sh in a desiccator 
and weigh ( M2). 
A.4 CALCULATION  
The moisture content, expressed as percent by mass, shall be calculated as follows:  
 100 𝑥 (𝑀1−𝑀2 )
𝑀1−𝑀 
Where,  
𝑀  is the mass , in grams, of the dish, its cover and the stirring rod;  
𝑀1 is the mass, in grams, of the dish, its cover and the stirring rod with the sample before drying, and,  
𝑀2  is the mass, in grams, of the dish, its cover and the stirring rod with the sample after drying.  
 
 
 
 
 
 
 
 
 
 
  
 6  
Annex B  
(Normative)  
 
TEST FOR DISPERSIBILITY IN WATER  
B.1 APPARATUS  
B.1.1  Beaker , 400 ml. 
B.1.2  Measuring cylinder,  100 ml and 1000m l. 
B.1.3  Thermometer . 
 
B.2 REAGENT  
B.2.1  Distilled water . 
 
B. 3 PROCEDURE  
B. 3.1  Dry baker’s yeast  
Weigh 5 g of dry baker’s yeast into a 400 ml beaker and add 50 ml of disti lled water at 40 °C. Leave the product 
undisturbed for 5 min and thereafter, stir for 2 min. To a one -litre graduated c ylinder, add 900 ml of distilled 
water at 40 °C. Pour the slurry in the beaker into the water in the gradu ated cyli nder. Wash the beaker with 50 
ml of distilled water, pour it into the cylinder and leave it undisturbed for  5 min. Check for any deposits at the 
bottom of the cylinder. If no deposits appear at the bottom of the c ylinder, the material shall be considered t o 
have passed the test.  
B.3.2 Fresh baker’s yeast  
Weigh 20 g of fresh baker’s yeast into a 400 ml beaker and add 50 ml of disti lled water at 40 °C. Leave the 
product undisturbed for 5 min and thereafter, stir for 2 min. To a one -litre gra duated cylinder, a dd 900 ml of 
distilled water at 30 °C. Pour the slurry in the beaker into the water in the gradu ated cylinder. Wash the beaker 
with 50 ml of distilled water, pour it into the cylinder and leave it undisturbed for  5 min. Check for any deposits 
at the bottom  of the cylinder. If no deposits appear at the bottom of the c ylinder, the material shall be considered 
to have passed the test.  
Note:  If starch was added to the yeast, it may form a sediment, which  may contain a few yeast cells.  
 
 
 
 
 
 
 
 
  
 7  
Annex C  
(Normative)  
 
DETERMINATION OF FERMENTING POWER  
C.1 APPARATUS  
C.1.1  Fermentometer.  The assembly of the apparatus is illustrated in Figure 1. It consists of a 250 ml flat -
bottomed flask ( A), whose mouth is fitted with a ground -glass joint having a gla ss delivery tube bent at right 
angle. It is connected to a three -way T -shaped stop -cock ( B) which in turn is fit ted on a 100 ml graduated tube 
(D) of the manometer. E is the manometer reservoir of 250 ml capacity. I is the iron stand. D and E are 
connected by a PVC tube F. G is a water  bath.  
C.1.2  Barometer . 
C.1.3  Thermometer . 
 
C.2 REAGENTS  
C.2.1  Sugar phosphate mixture.  Grind and mix thoroughly 400 g of sucrose, 25 g of diammonium hydrogen 
phosphate [(NH4) 2 HPO 4] and 25 g of di potassium hydrogen phosphate (K 2 HPO 4). 
C.2.2  Calcium sulphate solution.  Dilute 30 g of saturated calcium sulpha te solution (CaSO 4 .2H 2 O) with 
70 g of distilled water.  
C.2.3  Manometer solution.  Weigh 200 g of anhydrous calcium chloride a nd 10 g of cupric chloride and 
dissolve in distilled water. Add a little hydrochloric acid so that the final pH after  making up the solution to two 
litres does not exceed 5.0.  
 
Figure 1:  Fermentometer apparatu s 
 
 8  
C.3 PROCEDURE  
C.3.1  Mix 6.75 g of the sugar phosphate mixture with 75 ml of the calcium  sulphate sol ution in the flask. Add 
to it, 3.67 g of fresh baker’s yeast or 0.893 g of dry baker’s yeast. Stir well to dispers e the yeast. Keep the flask 
in the water bath  at 30 °C througho ut the experiment. Bring the three -way T -shaped stop -cock of the 
manometer into a position which allows displacement of initial air (by the carbon dio xide evolved) to escape to 
the atmosphere without displacement of the manometer fluid. This displacement i s allowed for the first 13 min 
after which the stop -cock position is altered to allow the carbon dioxide evol ved to enter the manometer and 
bring about the displacement of the manometer fluid. Shake the cont ents of the flask every 10 min.  
C.3.2  While takin g the reading of the gas evolved, the level of the fluid in the manometer shal l be adjusted 
by sliding the reservoir arm of the manometer and the volume of gas evolved at this pre ssure (which will now 
be equal to the atmospher ic pressure) shall be recorded.  
C.3.3  As soon as the reading is taken, the initial gas formed which has just been measured, is allowed to 
escape into the atmosphere by operating the three -way stop -cock and the stop -cock posi tion is again adjusted 
to take the second reading. For  fresh baker’s yeast, readings should be taken every 10 minutes and for dry 
baker’s yeast, readings shall be taken every 30 min. In both the cases, r eadings shall be taken for 3 h.  
C.3.4  The room temperature and the atmospheric pressure shall also be noted  during  the course of the 
experiment. The readings are recorded in a tabulated form (see Table C.1) and the t otal volume of gas 
produced is calculated and corre cted at 101 kPa pressure and 20 °C tempera ture by the formula given in C.4. 
Table C.1 – Recording  carbon dioxide evolved every 10/30 min  
Time  Volume of CO 2 
evolved (ml)  Room 
temperature (0 C) Atmospheric 
pressure (mmHg)  Corrected volume 
(ml) 
10:00 am  ………….  ………….  ………….  ………….  
10:10 am  ………….  ………….  ………….  ………….  
10:20 am  ………….  ………….  ………….  ………….  
10:30 am  ………….  ………….  ………….  ………….  
10:40 am  ………….  ………….  ………….  ………….  
………….  ………….  ………….  ………….  ………….  
………….  ………….  ………….  ………….  ………….  
1:00 pm  ………….  ………….  ………….  ………….  
 Total volume  Average 
temperature  Average pressure   
 
C.4 CALCULATION  
The fermenting power, expressed  as corrected volume in millilitres, shall be expressed as follows:  
  𝐶𝑜𝑟𝑟𝑒𝑐𝑡𝑒𝑑  𝑉𝑜𝑙𝑢𝑚𝑒  =Observed  volume  x Observed  average  pressure  x293
760  x273 +Average  room  temperature 
The mass of carbon dioxide evolved, expressed in grams, may be calculated  from this corrected volume as 
follows:  
  𝑚𝑎𝑠𝑠  𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛𝑑𝑖𝑜𝑥𝑖𝑑𝑒  𝑒𝑣𝑜𝑙𝑣𝑒𝑑 =44 x V
22400 
Where,  
V is the corrected v olume of carbon dioxide evolved . 
  
 9  
Annex D  
(Normative)  
 
DETERMINATION OF DOUGH RAISING CAPACITY  
D.1 APPARATUS  
D.1.1  Beaker , 500 ml . 
D.1.2  Measuring cylinder , 100 ml . 
D.1.2  Calibrated weighing balance . 
 
D.2 MATERIALS  
D.2.1  Wheat flour  conforming to MS 30  
D.2.2  Sucrose . 
 
D.2 PROCEDURE  
D.2.1  Mix 4.0 g of fresh baker's yeast or 1.0 g of dry baker's yeast with 100 g of wh eat flour. Add 1.0 to  
1.5 g of sucrose and a suitable quantity of water (about 55 ml). Knead well. Press th e resulting dough into a 
glass beaker. Note the level of the dough by means of a scale, from the bottom of t he beaker. Keep it cover ed 
for one hour at 27 °C. At the end of thi s period, note the level again.  
D.2.2  The product shall be deemed to have satisfied the test if the rise in level is at le ast 80 percent of the 
original for dry baker’s yeast and 110 % for fresh baker’s yeast . 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 10  
Annex E  
(Normative)  
 
DETERMINATION OF BACTERIAL ROPE SPORE COUNT  
E.1 APPARATUS  
E.1.1  Flask , 100 ml . 
E.1.2  Conical flask , 250 ml . 
E.1.3  Water bath . 
E.1.4  Pipette , 1 ml and 10 ml . 
E.1.5  Petri dishes . 
 
E.2 REAGENTS  
E.2.1  Sterilised peptone water, 0·1 %  
E.2.2  Tryptone glucose extract (TGE) Agar composed of:  
E.2.2.1  Tryptone 5.0 g;  
E.2.2.2  Agar, bacteriological grade, 15.0 g. Granulated or chopped shreds, prac tically free from thermophilic 
bacteria shall be used;  
E.2.2.3  Yeast extract 2.5 g;  
E.2.2.4  Distilled water, one litre;  
E.2.2.5  Sodium chloride 6.5 g;  
E.2.2.6  Glucose (dextrose) 1.0 g; and  
E.2.2.7  Final pH of 7.0 ± 0.1.  
 
E.2 PROCEDURE  
E.2.1  Weigh 22 g of wheat flour in a suitable sanitised container and transfer to a coni cal flask containing 
100 ml of sterile 0.1 % peptone water and sterile sand or glass beads. Blend on a shaker for about two minutes. 
Dilute the blended mixture further,  1:10, 1:100, 1:1 000, 1:10 000, etc., by dilution te chnique, using sterile 
peptone wate r. 
E.2.2  Prepare tryptone glucose extract (TGE) agar; 100 ml per 250 ml conical flask. P repare one additional 
flask of medium to serve as ster ility control. Sterilise at 121 °C for 15 min and then  cool to 45 °C in a waterbath. 
Pipette volumes of the blended mixture into a series of TGE agar flasks while t hey are held in the waterbath; 
10 ml into the first, 1 ml into the second and 1 ml of each dilution into the third, fourth and fifth TGE flask and 
so on. Gently agitate the flasks to disperse the blended mixt ure throughout the medium.  
E.2.3  Transfer the flasks without dela y to a waterbath adjusted to 65°C to 90 °C and hold for 30 min with 
gentle shaking occasionally to assist heat distribution. After 30 min of heat treatme nt, cool the flasks to about 
45°C witho ut allowing the agar to gelatinise. Pour 100 ml of the medium into each flask representing the 
product and sterility control into a set of five sterile petri dishes in approximately eq ual volumes of about 20 ml 
per plate. When agar has solidified, invert t he plates and incubate at 35 °C for 48 h.   
 11 E.2.4  Count the surface and sub -surface colonies. The sum of the colonies on the set of five pl ates poured 
from TGE agar, containing 10 ml of the blended mixture represents the number of  aerobic and mesophilic 
spore s per gram of the product. Similarly, 1 ml of the blended and 1 ml of each dilu tion are equal to 0.01, 
0.001, 0.000 1 and 0.000 01 of the number of spores per gram and shall be multipl ied by the respective dilution 
factor. Generally, the set of plates showing about 30 to 60 colonies per plate are to be chosen for the counting  
purposes.   
 
E.3 PRECAUTIONS AND LIMITATIONS  
E.3.1  The procedure permits enumeration of aerobic and mesophilic spores in food  samples containing 
relatively higher number of spores b y higher dilution of the samples prior to heat treatment.  
E.3.2  Certain thermophilic strains may also be indicated in this method in whi ch case a separate 
enumeration method for thermophiles may be adopted and their numbers subtracted from the spore count  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 12 Annex F  
(Normative)  
 
DETERMINATION OF BACTERIAL FLORA OTHER TH AN YEAST  
F.1. METHOD 1  
 
F.1.1  APPARATUS  
F.1.1.1  Sterile weighing scoop – with counterweight . 
F.1.1.2  Sterile bac teriological transfer pipettes – accurancy  graduated and with non -absorbent cotton plug 
in the sucking end . 
F.1.1.3  Sterile dilution flasks – made of heat resistant glass . 
F.1.1.4  Sterile petri dishes  – outside diameter 100  mm, with inside diameter 90  mm and depth 16  mm. The 
exterior and interior surfaces of the bottom shall be flat and free from bubbles, scratches or other defects.  
F.1.1.5  Sterile bacteriological tubes – of 25  ml capacity with a mark at the 10  ml level and fitted with a non -
absorbent cotton plug.  
 
F.1.2  REAGENTS  
F.1.2.1  Sterile citric  acid solution – prepare an approximately 10% (m/v) solution of citric acid in water and 
sterilise it in an autoclave at 1200 C for 15 minutes.  
F.1.2.2  Dextrose agar medium – having the following composition: peptone 20  g, dextrose 40  g, agar 25  g 
and distilled water 1000  ml. 
F.1.2.2.1  Preparation of the dextrose agar medium  
Steam the ingredients to dissolve and filter through chardin filter paper at 600 C, sterilise this in an autoclave 
at 1200 C for 15 minutes. Cool to about 900 C and adjust to pH 3.5 with the sterile citric acid solution  (F.1.2.1 ). 
Pour the medium into each of the sterile bacteriological tubes  (F.1.1.5 ) up to the 10ml mark (do not sterilise 
again).  
F.1.2.3  Nutrient agar medium – having the following composition: beef extract 3  g, peptone 6  g, agar 25  g 
and distilled water 1000  ml. 
F.1.2.3.1  Preparation of nutrient agar medium  
Steam the ingredients to dissolve. Adjust to pH 6.2 to 7.2. Boil the medium and filter through chardin filter 
paper at 600 C. Pour the medium into the bacteriological tubes up to 10  ml mark and sterilize in an autoclave 
at 1200 C for 15 minutes.  
F.1.2.4  Ringer’s solution (full strength) - having the following composition: sodium chloride (NaCl) 9.0  g, 
potassium chloride (KCl) 0.42  g, calcium chloride (CaC l) 0.24  g, sodium bicarbonate (NaHCO 3 ) 0.20  g and 
distilled water 1000  ml. 
F.1.2.4.1  Preparation of ringer’s solution  
F.1.2.4.1.1  Dissolve the ingredients and sterilize in an autoclave at 1200 C for 15 minutes.  
F.1.2.4.1.2  Dilute the Ringer’s solution to four times with sterile distilled water before use.  
  
 13 F.1.3  PROCEDURE FOR DETERMINING YEAST CELL COUNT  
F.1.3.1  Dilution  – Prepare a dilution of the material in the Ringer’s solution F.1.2.4.1.2  so that 1ml of the 
diluted sus pension when plated as described in F.1.3.2  give between 30 and 300 colonies . Add 1 ml of this 
dilution to the sterile petri dishes. Use at least five dilutions.  
F.1.3.2  Pouring of plates  – melt the dextrose agar medium in the bacteriological test tubes F.1.2.2.1  and 
immediately cool to about 450C (prolonged heating at higher temperature hydrolyses the agar and affects the 
gelling properties of the medium). Pour this melted medium into the petri dishes and mix by rotating and tilting 
the dish without splashing over the edge. Allow to solidify.  
F.1.3.3  Incubation  – Invert the petri dishes and incubate at 300C for 3 days.  
F.1.3.4  Counting  – count the yeast colonies with the aid of magnification under uniform and properly 
controlled illumination. Count on ly those plates with 30 to 300 colonies.  
 
F.1.4  PROCEDURE FOR DETERMINING TOTAL PLATE COUNT  
F.1.4.1  Dilution – prepare a dilution of the material in the Ringer’s solution F.1.2.4.1.2  so that 1ml of the 
diluted suspension w hen plated as described in F.1.4.2  give between 30 and 300 colonies . Add 1 ml of this 
dilution to the sterile petri dishes. Use at least five dilutions.  
F.1.4.2  Pouring of plates  – melt the nutrient  agar medium in the ba cteriological test tubes F.1.2.3.1  and 
immediately cool to about 4500C. Pour this melted medium into the petri dishes and mix by rotating and tilting 
the dish without splashing over the edge. Allow to solidify.  
F.1.4.3  Incubation  – Invert the petri dishes and incu bate at 370C for 2 days.  
F.1.4.4  Counting  – count the colonie s with the aid of magnification under uniform and properly controlled 
illumination. Count only those plates with 30 to 300 colonies.  
 
F.1.5  CALCULATION  
F.1.5.1  Calculation for yeast cell count  
F.1.5.1.1  Complete the average yeast cell count per gram from the dilution used.  
F.1.5.1.2  Yeast cell count per gram (on dry basis):  
   yc=100x cw
100 −M 
Where,  
cw is the average yeast cell count per gram F.1.5.1.1 ; and  
M is the moisture, percent by mass , as determined in annex A.  
F.1.5.2  Calculation for bacterial flora other than yeasts  
F.1.5.2.1  Complete the average total plate count per gram from the dilutions used.  
F.1.5.2.2  Total plate count per gram (on dry basis):  
   𝑇𝑐=100  x Tw
100 −M 
  
 14 Where,  
Tw is theaverage total plate count per gram , F.1.5.2.1;  and 
M is the moisture, percent by mass , as determined in annex A.  
F.1.5.2.3  Bacterial flora other than yeasts, count per gram (on dry basis) = T C – YC 
Where,  
Tc  is the total plate count per gram (on dry basis); and  
Yc  is the Yeast cell count per gram (on dry basis).  
 
F.2 METHOD 2  
 
F.2.1  PRINCIPLE  
The growth of yeast cells is inhibited by addition of chemicals such as nystatin or cycloheximide (actidione) 
and the material in a suitable medium is incubated at 370 C for 48 hours. The bacterial flora other than yeast 
is then counted.  
 
F.2.2  APPARATUS  
Same as given from F.1.1.1  to F.1.1.5.  
 
F.2.3  REGAENTS  
F.2.3 .1 Nystatin or cycloheximide (acti dione) solution – 0.22 % (m/v), sterilised at 36  kPa for 20 minutes.  
F.2.3 .2 Yeast suspension (m/v basis) – dilution 10-1 to 10-6 . 
F.2.3 .3 Nutrient agar and yeast extract medium.  
F.2.3.3.1 Nutrient agar – having the following composition: Bacto beef extract 3.0  g, bacto peptone  
5.0 g, sodium chloride 8.0  g, bacto agar 15.0  g, distilled water 1000  ml and pH 7.0.  
F.2.3 .3.2  Suspend nutrient agar in water (23  g/litre of water) and add 10  g of yeast extract. Heat in the boiling 
water bath to dissolve. Dispense the agar (12  ml) while hot into test tubes and cover with oxold caps. S terilise 
by autoclaving at 100  kPa for 15 minutes.  
 
F.2.4  PROCEDURE  
F.2.4 .1 In each petri dish, first pour 1ml of nystatin or cycloheximid e solution (0.12  %, m/v), then pou r 1 ml of 
the appropriate dilution of yeast suspension and finally one tube of nutrient ag ar medium F.2.2.3.1  at a 
temperature of 45 to 460 C and mix by rotating and tilting the dishes without splashing over the edge. Allow to 
solidify.  
F.2.4 .2 When set, invert the petri dishes and incubate for 48 hours at 370 C. 
F.2.4 .3 Count each colony and multiply the total by the appropriate dilution used.  
F.2.4 .4 Compute average count per gram of bacterial flora other than yeast (N).  
  
 15 F.2.5  CALCULATION  
Bacterial flora other than yeast, per gram (on dry basis)  =100  x N
100  X M 
Where , 
N is the average count per gram of bacterial flora other than yeast; and  
M is the moisture , percent by mass, as determined in annex A.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 16 Annex G  
(Normative)  
 
SAMPLING OF BAKER’S YEAST  
 
G.1 GENERAL REQUIREMENTS OF SAMPLING  
In drawing, preaparing, storing and handling samples the following precautions and directions shall be 
observed.  
G.1.1  The sampling instrument shall be clean and dry when used. When taking samples for microbiological 
examination, the sampling instrument shall be sterile.  
G.1.2  Precuations shall be taken to protect the samples, the materials being sampled, the sampling 
instruments and the containers for samples,  from adventitious contamination such as damp air, dust and soot.  
G.1.3  The samples shall be placed in cl ean and dry glass containers. The sample containers shall be of such 
a size that they are almost completely filled by the sample. The sample container shall in addition be sterile 
when they are used for storing samples for microbiological examination.  
G.1.4 Each container shall be sealed air tight  after filling and marked with full details of sampling,  batch 
number, name of the manufacturer and other important particulars of the consignment.  
G.1.5  Fresh baker’s yeast samples shall be refrigerated immediatel y at a temperature between 1 – 50 c and 
shall be tested within 24 hours. Dry baker’s yeast shall be refrigerated immediately and tested within 48 hours.  
G.1.6  Sampling shall be done by a person agreed to between the purchaser and the vendor and in the 
presence of the purchaser (or his representative) and the vendor (or his representative).  
 
G.2 SCALE SAMPLING  
G.2.1  Lot 
All the containers in  a single consignment of the material of same type and drawn from a single batch of 
manufacture shall constitute a lot.  If the consignment is declared to consist of different batches of manufacture, 
containers of the same batch shall be separated and shall constitute separate lots.  
G.2.2  For ascertaining the conformity of material to the requirements of this specification,  samples  shall be 
tested from each lot separately.  
G.2.3  The number of containers to be selected from the lot shall depend on the size of the lot and shall be 
according to Tables  G.1 and G.2. 
Table G.1 – Scale of sampling of Fresh Baker’s Yeast (FBY)  
S/N Number of packets in the lot  Sample size  
1 Up to 50  2 
2 51 t0 100  3 
3 101 to 150  5 
4 151 to 300  7 
5 300 and above  10 
 
 
 
  
 17 Table G.2 – Scale of sampling for Dry Baker’s Yeast (DBY)  
 
G.2.3.1  In case of Fresh Baker’s Yeast, if packets are packed in cartons, 25  % of the cartons subject to the 
minimum of two shall be selected and approxiamately equal number of packets shall be selected from each 
carton. In case the cartons are packed in wooden bo xes, at least 255 of the wooden boxes subject to the 
minimum of two shall be selected and one carton from each such wooden box shall be selected, in order to 
obtain the requisite sample size according to Table G.1,  approximately equal number  of packets sha ll be taken 
from each carton.  
G.2.3.2  In case of Dry Baker’s Yeast, if containers are packed in wooden boxes, at least 25  % of the wooden 
boxes subject to the minimum of two shall be selected and approximately equal number of containers selected 
from each wooden box.  
G.2.3.3  The containers from the cartons/wooden boxes and cartons from wooden boxes shall be selected at 
random from the lot.  
 
G.3 TEST SAMPLES AND REFERENCE AMPLES  
G.3.1  Preparation of sample for microbiological examination  
In order to draw a representative sample from each container selected, take small portions of the material from 
a container with an appropriate sampling instrument which is sterile and mix them thoroughly under aseptic 
conditions. The quantity of material in the sample shall  be not less than 100  g. Divide the sample (taking care 
not to bring in microbiological  contamination in the material) into three equal parts; each part shall form reduced 
sample for that container. A set of such reduced samples, consisting of one reduced sample for each container, 
shall constitute the test sample. Three sets of these test samples, each being not less than 25  g, shall be 
transferred to sterile glass containers, sealed air tight and labelled with particulars given in G.1.4.  They shall 
be marked, in addition with the words ‘ For microbiological examination’.  
G.3.2  Preparation of sample for other tests  
Draw from the portion remaining after taking sample for microbiological examination fro m each container in 
the sample, at least  400 g of the container and mix thoroughly so as to form a representative sample for that 
container. Divide this into three equal portions. Each portion, not being less than 100  g shall be transferred to 
a clean dry container made of glass or tinplate and labelled with particulars given in G.1.4.  Three sets of test 
samples shall be prepared and in addition, be marked with words ‘For tests other than microbiological’.  
G.3.3  Sample for purchaser o vendor  
A set of test samples, consisting of two reduced samples  namely one marked ‘For microbiological examination’ 
and the other ‘For tests other than microbiological’, for each container in the sample , shall be sent both to the 
purchaser and the vendor.  
 
 S/N For containers of less than 100  g For containers of 100  g to 
1 kg For containers (tins) of 15  
kg 
1 Lot size  Sample size  Lot size  Sample size  Lot size  Sample size  
2 Up to 100  5 Up to 50  2 Up to 50  2 
3 101 to 300  7 51 to 150  3 51 to 150  3 
4 301 and above  10 151 to 300  5 151 and 
above  4 
5   301 and 
above  7    
 18 G.3.4  Reference sample  
The third set of test samples, consisting of the two reduced samoles, namely one marked ‘For microbiological 
examination’ and the other ‘For tests other than microbiological ’, beari ng the seals of the  purchaser and the 
vendor, shall constitute the reference sample to be used in case of a dispute between the purchaser and the 
vendor.  
G.3.5  The samples labelled with words ‘For microbiological examination’ shall be used for determination of 
the bacterial flora, other than yeast.  
G.3.6  The samples labelled with words ‘For tests other than microbiological’, shall be used for all other tests.  
 
G.4 NUMBER OF TESTS AND CRITERIA FOR CONFORMITY  
G.4.1  All the characteristics given in Table 1  shall be tested on individual samples.  
G.4.2  Microbiological requirements shall be tested on individual sam ples labelled with the words ‘For 
microbiological examination’.  
G.4.3  The lot shall be declared as conforming to the requirements of this specification if all the individual test 
results according to G.4.1  and G.4.2  meet the relevant specification requirements.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 19 
ICS 67.220.20         DMS 1257 :2023
                                                                                   Second  edition  
 
 
 
 
 
 
THE MALAWI BUREAU OF STANDARDS              CERTIFICATION MARK SCHEME  
The Malawi Bureau of Standards is the 
standardizing body in Malawi under the aegis 
of the Ministry of Trade  and Industry .  Set up in 
1972 by the Malawi Bureau of Standards Act 
(Cap: 51:02), the Bureau is a parastatal body 
whose activities aim at formulating and 
promoting the general adoption of standards 
relating to structures, commodities, materials, 
practices, operations and from time  to time 
revise, alter and amend the same to 
incorporate advanced technology.  To bring the advantages of standardization 
within the reach of the common consumer, the 
Bureau operates a Certification Mark Scheme. 
Under this scheme, manufacturers who 
produce goods that conform to national 
standards are granted permits to use the 
Bureau’s “Mark of Quality” depicted below on 
their products.  This Mark gives confidence to 
the consumer of the commodity’s reliability.