(10 pm. – promoted by ek hornbeck)
Of all foodstuffs, milk is unique in that it provides all of the nutritional needs for infant mammals. In addition to nutrition, it also supplies essential antibodies the first few days to newborns. Milk is unique to mammals, and is one of the reasons that mammals had the evolutionary advantage that they had when they arose during the age of reptiles.
However, humans are also unique in that we are one of the few mammals who continue to take it after infancy, and the only species that continues to take it after adolescence and into adulthood. Milk is far from the perfect food for adults, but certainly can be part of healthy diet.
Humans are also unique in that we are the only species that takes milk in a natural setting from other species. By that I mean that we actively collect it, not like giving the cat a saucer of milk. The nutritive value of milk is species specific, and our habit to taking cows’ milk (for the most part) is quite unnatural.
For the purpose of this discussion we shall focus on cows’ milk, although there are some notable exceptions such as the milk from sheep, goats, houses, Asian buffaloes, and some other species. By far, cow’s milk sees the greatest human consumption. I personally love milk, and now drink mostly skim milk, although I do buy whole buttermilk. Like clockwork, I consume a gallon of skim milk and half a gallon of buttermilk every week. This amounts to about 2500 calories per week, or around 350 per day.
All cow’s milk is not the same, although factory produced milk is pretty standard because of the means of production. Most US milk is produced by the big black and white Holstein cows, mostly because they are extremely large producers on a volume basis. However, Holstein milk is not as “rich” (meaning as high in butterfat) as milk from other breeds, notably Jerseys and Guernseys. Often to make whole milk reach the 3.25% milkfat minimum US standard, milk from richer breeds is blended with Holstein milk, but with the increasing popularity of reduced fat milk and the lessening popularity of butter, that is not as common as it once was.
Milk, although it looks simple in a glass, is an amazingly complex substance. There are hundreds of chemical compounds in milk, the largest one being water. Carbohydrates come next, in the form of the milk sugar lactose. Lactose is almost unique to milk, being found only in a very few other sources. Milk contains around 5.25% lactose. Lactose is a sugar, and milk contains about half the sugar that is found in soft drinks. The reason that milk does not taste very sweet is that lactose is only about 20% as sweet as sucrose.
Lactose presents a problem for many people because after infancy the enzyme needed to digest it, lactase, in general diminishes to the point that it is no longer digested, but rather fermented by yeasts in the GI tract. This causes flatulence, bloating, pain, and often diarrhea in those who are intolerant to lactose. This is a genetic thing, because there are several populations who maintain adequate lactase levels into adulthood. Northern Europeans and people from India generally can digest lactose, but only about 30% of people of African heritage can. There are a couple of things that can be done, one of which is to add bacteria (the so called acidophilus milk). A better way is to pass the milk over commercially produced lactase which predigests the lactose into the simple sugars glucose and galactose. These are readily absorbed and do not cause any problem. However, since they are sweeter than lactose, this milk tastes sweeter than regular milk. Actually, most lactose intolerant people can drink limited amounts of regular milk, up to about a cup per day, without any real problem.
The next most abundant nutrient is milkfat, at 3.25% minimum by federal standard for whole milk. This provides almost half of the calories in milk, and is fairly highly saturated. Although in reasonable amounts milkfat is not that big a deal, the typical American diet has way too many calories in it already, so cutting back on milkfat is probably a good idea for many people.
Next in abundance is protein, at about 3.2%. This is excellent protein, well balanced and readily digestible. However, one of these proteins is phenylalanine, and in infants with phenylketonuria milk must be severely restricted. This applies to human milk as well, and special infant formulas with reduced phenylalanine are available. By the way, no infant should be fed cow’s milk. Human milk is by far the best food for infants, but some formulas are fairly good for normal infants.
After that come the micronutrients vitamins and minerals such as sodium, potassium, and especially calcium. Milk is an important source of calcium for many people, and especially for children whose bones are forming it is an important part of their diet unless other factors interfere.
When I was a lad, my grandmum kept a Guernsey cow named Boney Maroney. She would milk her every morning and evening (cows have to be milked twice per day), and I well remember her sitting the milkpail on the kitchen table for the cream to rise. She would take the cream, or rather part of it, and churn it to butter, and the rest was either mixed back into the milk or used to make whipped cream, ice cream, or just to use plain on fruit and shortbread. It was good stuff. She kept the whole family in milk for a long time, until we had to move to North Little Rock. Boney got sold then, and my grandmum cried over selling the cow.
Boney was a free range cow, and the taste of the milk changed as her forage changed with the seasons. The spring milk was very flavorful because of the lush grass and other plants that she would eat then. Except for a very few people who still keep a cow, no one remembers how milk used to change with the seasons. The milk that we had was raw milk, with absolutely no treatment except for chilling. These days it is almost impossible to buy raw milk because of FDA regulations, and with good reason. Back when commercially produced milk first came out, thousands of people, in particular children, were sickened with tuberculosis and other milk borne diseases that came from infected cows. This milk was pooled with milk from healthy cows and thus the whole batch was contaminated. After pasteurization became the norm, these diseases, at least from milk, were eliminated. We shall discuss this process in a few minutes.
Most whole milk is also homogenized, which makes the cream stay suspended in the milk. When milk is homogenized, it is forced through very small orifices that break up the relatively large milkfat particles into much smaller ones that do not tend to float to the surface. This is for convenience and has nothing to do with health issues.
There are several methods to pasteurize milk. The least harmful to flavor is batch pasteurization, where a tank of milk is heated to 145 degrees F while being stirred, and that temperature held for half an hour. This is sufficient to kill pathogens, but does not “cook” the milk much. However, it still requires refrigeration because it is not sterile. This process is not very efficient of time or energy, so most milk today is pasteurized by the high temperature, short time process (HTST). In this process, the milk is heated to 162 degrees and held for 15 seconds. In practice, this is done by passing the milk through a heat exchanger continuously, being in the high temperature zone for the required amount of time. The third was to pasteurize milk is the ultrahigh temperature (UHT) process, where the milk is heated to nearly 300 degrees F in a pressurized heat exchanger and held for three seconds or less. This milk is truly sterile, and can be put up in coated paper boxes and stored on the shelf for months without going bad. However the flavor is severely compromised, being quite “cooked” tasting. In all three processes, the milk is cooled rapidly after pasteurization.
Most half and half and heavy cream is now processed by UHT, because with less sugar and protein than whole milk, the Maillard reactions that produce the cooked flavor and brownish color are of less significance.
Milk is produced in huge factories now, most of it being trucked in from various dairies, so the milk from thousands of cows is blended. Since most dairies are confined spaces and the feed is the same the year round, the seasonal variations are gone. However, I can taste a difference in milk bought from different stores, and I attribute that to subtle differences in the way that pasteurization was carried out. I am particular about my milk, and will do without rather then get it from a store that has what I consider to be bad tasting milk.
We have just scratched the surface of the topic this time, and next week we shall go more in depth about other milk products. I apologize for this being such short piece, and for the fact that I likely will be late in getting to comments tonight. I have an invitation to visit someone this evening, and those opportunities are important not to pass.
Doc, aka Dr. David W. Smith
Daily Kos, and