C.O.B - Clot On Boiling Test

Dairy Science

Clot . On . Boiling Test

Determination of Milk Acidity

Introduction

The normal pH of a natural milk produced ranges from 6.6 to 6.8 and of an acidity 0.13 to 0.18, this acidity is called the Natural Acidity due to some constituents which make up this acidity in milk such as Casein ( composed of α-casein, β-casein, and γ-casein), Whey protein ( composed of Lactoglobulin and Lactoalbumin), Salts ( e.g., Phosphates, Citrates, Nitrogen, Potassium, Zinc, Boron, etc...) and CO2

Leaving milk under normal temperature such as room temperature, this allows for the growth of bacteria present in the milk especially the Lactic acid bacterial strains which converts the Lactose ( milk sugar) to Lactic acid by fermentation decreasing the pH and increasing the milk acidity, and this acidity is called Developed Acidity; Because it came/rose or developed from an organism which is in our case the Lactic acid bacteria.

There are qualitative and quantitative methods of acidity determination for milk bulks in factories/plants and usually we measure the acidity by measuring lactic acid percentage, and in this case we call it '' Total Titratable Acidity ''.

Why do we need to determine acidity in milk?

Because it is important for the manufacture of some dairy products, quality of milk, and the milk stability during some technological treatments.

Clot . On . Boiling Test

It is a qualitative method of acidity determination in milk, we conclude from the test name is that we are counting on the formation or the appearance of Clots in the milk sample, so the milk will be clotted if acidity is 0.25% and more

Tools needed ( Home )

• Pipette
• Beaker ( will be used as a hot water bath)
• Test tube
• Milk sample
• Flame source

Procedures

1. Put 5 ml. of milk in clean test tube.
2. Put the test tube in boiling water bath until boiling of the sample.
3. Notice the presence of clots, if present it will be positive result, If not, then it will be a negative result.

+ve result - By me 

The formation of clots indicates the high acidity of the milk, and perhaps you could ask how I received an acidic milk sample:

 Basically, I took like an amount of 200 ml., and a tablespoon of yoghurt ( containing a Lactic acid bacteria Bifidobacterium sp., and Lactobacillus sp.), and left them for about a day in room temperature until a curd was formed. Yet the whole sample wasn't curd, Once a curd was formed I managed to take 5 ml. and perform the test.

I hope you gentlemen and ladies find this informative and if you do please do share it with your science buds and follow my blog for new topics.

I will upload a complete video explaining all the steps in case you find something difficult or how you going to perform this test at home - so the video COMING SOON...

Next one in our dairy science episodes laboratory work experiments will be the quantitative method of milk acidity determination..., the scientific method. STAY TUNED

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