DAIRY TECHNOLOGY: MILK PROCESSING
Diagram
Homogenized milk and non-homogenized milk side by side
Homogenized milk
Milk forced through a tiny valve under pressure: fat globules break into tiny droplets that stay mixed.
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Non-homogenized milk
Milk left as it is: fat globules stay large and float up as a cream line.
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The core difference
Fat globule size. Homogenization stops the cream from rising; it does not change the amount of fat.
Figure 1: Homogenized milk compared with non-homogenized milk. Drawn in our own style from A. K. M. Humayun Kober, Milk and Dairy Foods: Nutrition, Processing and Healthy Aging, CRC Press, 2024, Ch. 2. Note: the sources cover homogenization at chapter level, and the comparison below says plainly where the books give no standard procedure for this pair.
Introduction
Homogenized milk and non-homogenized milk have the same fat, the same protein and the same nutrients. The difference is only in the size of the fat globules.
The core difference is the cream line. In non-homogenized milk the fat floats up and forms a cream layer on top. In homogenized milk the fat is broken into tiny droplets that stay spread through the milk, so the milk looks uniform from top to bottom.
Quick comparison
Table 1: Homogenized Milk compared with Non-Homogenized Milk
| Aspect | Homogenized Milk | Non-Homogenized Milk |
|---|---|---|
| Fat globule size | Very small, about 1 micrometre or less | Large, about 3 to 5 micrometres |
| Cream line | No cream line, fat stays mixed | Cream rises and forms a visible line on top |
| How it is made | Milk forced through a homogenizer valve under high pressure | No homogenization step, milk is only pasteurized |
| Fat content | Unchanged, the same as the starting milk | Unchanged, the same as the starting milk |
| Appearance | Uniform white from top to bottom | Cream layer on top, thinner milk below |
| Mouthfeel | Slightly thicker and smoother, fat spread evenly | Thinner below the cream, rich on top |
| Flavour | Mild, even flavour in every sip | Mild, with a rich first sip from the cream |
| Digestibility | Slightly easier fat digestion, more surface for enzymes | Normal digestion |
| Use in cooking | Even fat in sauces and baking | Cream can be skimmed off the top for cooking |
| Shelf behaviour | Stays uniform through its shelf life | Cream line grows as the milk stands |
Scientific explanation
Definition
Homogenized milk is milk that has been forced through a narrow valve under high pressure so that its fat globules are broken into much smaller droplets.
Non-homogenized milk is milk that has not had this treatment. Its fat globules stay at their natural size and rise to the top on standing.
Working principle
Fat globules rise because fat is lighter than the water part of milk, and large globules rise fast. Breaking them into tiny droplets slows the rise so much that the fat stays mixed for the whole shelf life.
The new small droplets are coated with protein from the milk, which keeps them from joining back together. The total amount of fat does not change, only its size and spread.
Apparatus
A homogenizer: a high-pressure pump that forces milk through a narrow adjustable valve.
A microscope or a particle size analyser is used in the laboratory to check the size of the fat globules.
Measurement procedure
Warm the milk to about 60 degrees C, pump it through the homogenizer at high pressure, and check that no cream line forms after the milk stands for two days in the cold.
The books give no single standard procedure that names this pair, so the check above is the standard homogenization efficiency test used in dairy plants.
Factors affecting readings
Pressure and temperature decide the result: higher pressure makes smaller globules, and warm milk homogenizes better than cold milk.
The fat content matters: richer milk needs more pressure for the same result. A worn valve or a low pressure leaves large globules and a cream line returns.
Formulas and calculations
The books give no formula for this pair. Cream rising follows the rule that larger and lighter globules rise faster, but no formula is given in the sources for calculating the rise in milk.
Homogenization efficiency is checked by a test, not a calculation: the milk is left standing cold for 48 hours, and the fat in the top part is compared with the fat in the rest. Good homogenization gives almost no difference.
Industrial applications
- Homogenized milk: drinking milk sold in cartons, where a uniform look is expected.
- Homogenized milk: flavoured milk, cream and sauces where even fat gives an even texture.
- Non-homogenized milk: farmhouse milk and traditional milk where the cream line is valued.
- Non-homogenized milk: milk sold so the cream can be skimmed off the top at home.
- Both milks: cheese and yoghurt making, where homogenization is chosen or skipped for the texture wanted.
Advantages and limitations
- Homogenized milk advantage: uniform look and even flavour in every glass, no cream line.
- Homogenized milk limitation: needs a homogenizer, and some people prefer the natural cream line.
- Non-homogenized milk advantage: no extra processing, and the cream can be skimmed off for cooking.
- Non-homogenized milk limitation: the cream rises, so the first glass is rich and the last glass is thin.
FAQ
Does homogenization remove fat from milk?
No. It only breaks the fat into smaller droplets. The amount of fat stays exactly the same.
Is homogenized milk less healthy?
No. Its nutrients are the same as non-homogenized milk. Only the size of the fat globules changes.
Why does non-homogenized milk form a cream line?
Its fat globules are large and fat is lighter than water, so they float up and gather on top.
Can I homogenize milk at home?
Not properly. A homogenizer uses very high pressure through a tiny valve, which no home kitchen tool can match. Shaking the bottle only mixes the cream in for a short time.
Does homogenization affect cheese making?
Yes. Homogenized milk gives a softer curd, so cheese makers often skip homogenization for hard cheeses and use it for soft cheeses and yoghurt.
References and further reading
- A. K. M. Humayun Kober, Milk and Dairy Foods: Nutrition, Processing and Healthy Aging, CRC Press, 2024, Ch. 2 (homogenization) (Google Books page read)
- FTN books on disk: Market Milk, Dairy Processing Handbook by Bylund, Physical Chemistry of Milk (agrimoon dairy series).
