Dilutions

10X Dilutions

Generally, an initial 10X dilution is preparred from the  original sample.  Further dilutions are then made from this initial dilution.  In order to make this 10X dilution, follow the guidelines below for sample size and amount of diluent to use.

                  General Products                            Dairy Products

               Amt of sample     Amt of diluent                    Amt of sample      Amt of diluent

              10 mL or grams +   90 mL diluent                   11 mL or grams +   99 mL diluent

              50 mL or grams + 450 mL diluent                   55 mL or grams + 495 mL diluent

Solid samples:  Blend the sample with the diluent in a sterile blender for 2 minutes, or massage the sample with the diluent in a stomacher bag for 2 minutes.

Liquid samples:  Add the sample to the diluent in a sterile container (such as a diluent bottle or stomacher bag) and shake approximately 25 times.

Remove 1 mL from this 10X dilution and place in the Easygel bottle.  Swirl and pour into an Easygel petri dish.  Incubate, and count colonies.  Multiply the count by the dilution factor, which is 10.

100X Dilutions

                  General Products                              Dairy Products

              Remove 10 mL from the 10X dilution             Remove 11 mL from the 10X dilution

              and deposit in a new 90 mL diluent               and deposit in a new 99 mL bottle
              bottle.  Shake 25 times.                                    bottle.  Shake 25 times.

Remove 1 mL from this 100X dilution and place in the Easygel bottle.  Swirl and pour into an Easygel petri dish.  Incubate, and count colonies.  Multiply the count by the dilution factor, which is 100.

1000X Dilutions

              General Products                                Dairy Products

           Remove 10 mL from the 100X dilution           Remove 11 mL from the 100X dilution

           and deposit in a new 90 mL diluent                and deposit in a new 99 mL bottle
           bottle.  Shake 25 times.                                     bottle.  Shake 25 times.

Remove 1 mL from this 1000X dilution and place in the Easygel bottle.  Swirl and pour into an Easygel petri dish.  Incubate, and count colonies.  Multiply the count by the dilution factor, which is 1000.

Expected dilutions for various products

The following table recommends dilutions for total count, coliform, and yeast and mold testing.  However, some of these products may require testing for other organisms also.

Dilutions should yield between 30 and 300 colonies per dish.  This is for both accuracy and ease of counting.

If you do not know what count to expect from your product, try running a 10X and 1000X dilution. This will give you a good idea of what to expect for future dilutions.

 

 

 

Dilutions Overview