There's Milk and Milk

For a blog that talks about Italian food compared to its North American counterpart, milk is probably one of the less obvious choices of topic. But if cow milk is similar, the way Italians and North Americans look at it as a product can be quite different. For instance, it is perfectly normal for Italians to buy fresh milk with a shelf life of 2 days, as well as to buy milk meant to be stored unrefrigerated for months before consumption.

Before we venture ourselves into the different preservation techniques, let's talk for a moment about the relationship between Italians and milk. Italians like their milk just as much as North Americans do, but researches show that consumption of cold milk as a drink is less in adults. A glass of milk is appreciated, but isn't commonly available in coffee bars and especially in restaurants because Italians don't have milk with their meals. Flavored milk is also quite uncommon in Italy - chocolate milk does exist, but is only meant for young children (and is not as thick as the North American one). The consumption of milk-derived products, such as cheese, is instead higher in Italy.

Flavor-wise, Italian milk can taste quite different from the North American one. Flavor largely depends on how the cows are fed. For instance, a prevalently dry hay diet produces a mildly cheesy aroma, while lush pasturage produces sweeter flavors, but also barnyardy indoles⁽³⁾. Homogenization and pasteurization, which are nowadays standard for almost all milk, also affect the flavor.

Homogenization is a treatment developed in France around 1900 to prevent milk cream from rising to the top. The homogenization process breaks down the fat globules into smaller ones (from 4 μm to 1 μm). Caseine particles form a coating around the fat globules and this weights them down and interferes with their ability to clump, keeping them evenly dispersed in the milk. The structural changes introduced by homogenization cause the milk to taste blander, but also feel creamier, and appear whiter⁽³⁾.

The use of heat as a way to sanitize milk has been documented since the 1820s, but it took until the beginning of the 20th century for milk pasteurization to be regulated and required by the governments⁽³⁾. Raw unpasteurized milk can in fact be quite harmful, as it has a relatively high chance to become infected with dangerous bacteria including Salmonella and Listeria. Nowadays, raw milk is illegal in Canada, whereas in Italy and in the U.S. its commercialization is restricted to authorized farms (which must be frequently inspected) that can only sell directly to the public within their premises.

The effects of thermal processing on milk vary based on its intensity, and provide different levels of sanitation, shelf life extension, and side-effects on flavor and nutritional values. The following treatments are considered standard⁽²⁾:

• Thermalization: 20 seconds at ~65°C. The process kills many vegetative organisms and bacteria that produce enzymes that eventually cause milk deterioration. In the dairy industry, milk is often thermalized before undergoing further processing. Flavor and nutritional properties are unaltered.
  
  
• Low pasteurization: 30 minutes at 63°C, or 15 seconds at 72°C. The latter is referred to as Flash Pasteurization or HTST (high-temperature, short-time) and is considered the pasteurization standard for milk. It represents the minimal requirement by law in many countries (including Italy, the U.S. and Canada). Low pasteurized milk is safe to drink because all yeasts, molds and pathogen bacteria have been killed. However, bacterial spores and some enzymes are preserved. Even if refrigerated, shelf life is limited to 1 or 2 weeks (depending on the milk's "keeping qualities"). At strict HTST intensity, the flavor is almost unaltered and so are the nutritional properties. The slightly higher time and temperature (20 seconds at 75°C) required by homogenized milk is however sufficient to introduce small alterations.
  
  
• High pasteurization: 20 seconds at 85-100°C. This process, which essentially consists of a short boiling, kills all vegetative organisms and deactivates most enzymes (but still doesn't affect bacterial spores). High pasteurized milk has a longer shelf life, but is more vulnerable to post-processing contamination because the higher temperatures also eliminate the bacterial growth inhibitors. As a result, this type of pasteurization is usually operated on the bottled product. The milk serum starts to denaturate and a "cooked" flavor develops. The nutritional properties are slightly reduced because of a loss of vitamin C.
  
  
• Sterilization: 30 minutes at 110°C (prolonged boiling), or Ultra-High Temperature processes (UHT) ranging between 30 seconds at 130°C, and 1 second at 145°C. UHT milk (called "ultrapasteurized" in the United States) is preferred over milk sterilized by prolonged boiling because of the more limited browning and a better flavor. Shelf life is generally between 3 and 6 months, unrefrigerated. Once opened, it only lasts for 3-4 days at 4°C because natural bacteria inhibitors have been destroyed by the heating process. The nutritional value of UHT milk is reduced, but it is still a great source of essential nutrients such as calcium and proteins. UHT milk is particularly useful in all cases where transportation or storage of fresh milk is impossible, as well as for all uses that call for boiled milk. UHT milk is very common in Italy, where it represents almost 50% of the entire milk consumption, some Italians are used to its flavor and even prefer it over fresh milk. North America, instead, resists the introduction of UHT because of its flavor and because it's deemed not acceptable that milk can be stored unrefrigerated.

In recent years, the milk industry has devised an alternative to UHT which is also capable of extending shelf life, still without using preservatives. Through a process called "microfiltration", between 99.0 and 99.9% of bacterial cells (including most spores) are removed by using ceramic membranes with pore sizes of about 1 μm⁽²⁾. Since the fat globules are also about 1 μm in diameter, before microfiltration the milk's cream is separated, sterilized using a regular UHT treatment, and then added back. Microfiltered milk is nutritionally equivalent to regular pasteurized milk, but with a longer shelf life of up to 3-4 weeks, if properly refrigerated. Flavor-wise, it's considered very similar to regular pasteurized milk, but with a creamier texture.

Under the same storage temperatures, milk's shelf life depends on its "keeping quality", which derives from the quality of the raw milk, the type of pasteurization and the level of post-processing contamination⁽¹⁾. Keeping quality varies from country to country based on shelf life demand. In Italy, an expiry date of only a few days in the future is considered acceptable for milk, since it's quite common to buy fresh aliments daily. In North America, a minimum of 2 weeks is generally the requirement.

Because of the shorter shelf life of fresh milk, Italian milk is sold almost exclusively in 1 liter containers. UHT milk is also sold in 1 liter containers because of its limited expiry time once opened. North American milk instead supports larger formats up to 4 liters, or 1 gallon (in the U.S.).

Another important difference between Italian and North American milk is in the use of “fortification”. In Canada and the US, by law, vitamin A (a fat-soluble vitamin) is added to all skimmed milk to compensate for the amount that was removed when the milk was skimmed. Milk is also fortified with vitamin D, as regulated by law, to compensate for the lack of exposure of the cattle to direct sunlight. Italian milk has no additives.

Finally, as a summary of the differences, here is a comparison table.

	North American Milk	Italian Milk
Percentages of fat available	• Whole (3.5%, called Homogenized in Canada). • 2% or “Reduced fat”. • 1% or “Low fat”. • Semi-skimmed 1.8% (not available in Canada). • Skimmed (less than 0.5%).	• Whole (3.5% fat min). • Partly skimmed (1.5% to 1.8%). • Skimmed (less than 0.3%).
Retail sizes	Containers up to 1 gallon (4 liters in Canada).	Containers usually only up to 1 liter.
Fortification	Vitamins A added to all skimmed milk. Vitamin D added to all milk.	No vitamins added - vitamins are not even mentioned in the nutritional info.
Types of sanitation	• Raw milk - illegal in Canada, rare in the U.S. • Pasteurized: 2+ weeks shelf life at 4°C max. • Microfiltered pasteurized - not very common. 3-4 weeks shelf life at 4°C max. • Long preservation milk (UHT) - rarely available. Over 3 months shelf life at room temperature.	• Raw milk legal if sold on the premises from the producer. • Pasteurized milk(*) or Fresh Pasteurized milk(**): 6 days shelf life at 4°C max. • Microfiltered pasteurized milk. 2-3 weeks shelf life at 4°C max. • Long preservation milk (UHT). Over 3 months shelf life at room temperature.

(*) Milk proteins at least 11% of the total proteins.
(**) Pasteurization has to occur within 48 hrs from milking. Milk proteins at least 14% of the total (when over 15.5%, can be labelled "High Quality").


References

(1) Smit, G. (Editor). Dairy Processing : Maximising Quality. Cambridge, GBR: Woodhead Publishing, Limited, 2003.

(2) Walstra, Pieter. Dairy Technology : Principles of Milk Properties and Processes.
New York, NY, USA: Marcel Dekker, 1999.

(3) Harold McGee. On Food and Cooking: The Science and Lore of the Kitchen. Second edition (2004).