(10 pm. – promoted by ek hornbeck)
This is the third part of a four part series about milk. The first and second parts are here and here. The final installment will be about human milk with emphasis on its importance to the development of infants.
Cheese is one of the oldest processed food products known. Whilst the origins of cheesemaking are obscure, it is fairly easy to speculate on how it got started, and we shall look at that in due time. Archaeological evidence indicates that cheesemaking was an established art at least 4000 years ago, and the actual date of regular production is likely to be much older than that, but no records exist.
Because of the tremendous variety of cheese, I am sure not to mention one of your favorites. Please pardon that oversight, but I like to keep under 5000 words! However, I found an expert source that is likely to mention yours, and it appears directly under the fold.
I think that almost all of the varieties were legitimate, except for the beaver cheese. I just love Monty Python!
In any event, cheese is actually a range of products, produced from mammal milk, that have a few things in common (for the most part). With a few notable exceptions, almost all cheese is made from milk that has had an initial lactose fermentation, then treatment with a particular curdling agent, separation of the semisolid phase from the fluid phase, salting, and usually but not always an aging phase.
I am being fairly vague in this description because there are lots of variations. For example, authentic ricotta cheese is made from whey left over from other cheesemaking activities. Other cheeses do not undergo a lactic fermentation before the coagulating agent is added, whilst some others only undergo the lactic fermentation. Without getting into the gory details just yet, let us first discuss the typical process for making most kinds of cheese.
First, the milk is inoculated with the types of bacteria discussed last time for making yogurt or buttermilk. Either simultaneously of later, rennet is usually added to coagulate the protein in the milk further. This is a critical step, and we shall talk about that more. Soon most of the protein in the milk, and almost all of the casein, forms a firm network and this network is cut into smaller pieces to allow the whey to drain. Next, salt is added to the “new” cheese for reasons to be developed later. The amount of salt is highly variable, depending on the kind of cheese to be made. At this point, the curds may be lifted to make “fresh” cheeses like cottage cheese. With a high moisture content and low acid content, these fresh cheeses are quite perishable and need to be kept cold to stay good for a week or two. They do not have a lot of character, but are wholesome foods. For other, more aged cheeses, additional water removal steps are taken to make a product that will keep well.
There was a question about A1 casein and A2 casein. It turns out that there is a minor structural variation betwixt those two types of casein. Some people claim that A1 casein is unhealthy whislt A2 is healthy. The A1 type is produced by Holstein cattle, the most numerous dairy breed, and the A2 by Guernsey cattle. There is a company, the A2 Corporation, that advocates for A2 milk and claims that A1 milk is bad for people. First, beta casein (which is the casein that is either A1 or A2) makes up only about 30% of the protein in milk. Second, the difference is a single amino acid out of a chain of 209 amino acids. Whilst there MIGHT be some merit in the claims, no government agency has found the claims credible. I rooted around the web for quite a bit, and it turns out that the chief advocate for health benefits for A2 milk is the A2 Corporation.
We need to stop right here so that we understand rennet. With only a very few exceptions, all cheese is made with rennet, and it actually sort of defines what cheese is. Rennet is a complex of enzymes that are quite specific in the action on casein, the predominant milk protein. The really important one is chymosin, and modern cheesemaking usually uses it exclusively. Naturally, rennet is found in the forth stomach of ruminant animals before being weaned. Now we get into the history of cheesemaking.
In prehistoric times, bags that would hold liquids were hard to find, and almost all of them were internal organs of animals. There are several that can hold liquids well, including bladders, the single stomachs of nonruminant animals, and the multiple stomachs of ruminants. Very early on it was discovered empirically that if milk were put into the forth stomach, the abomasum, of a milkfeeding animal, the solid phase and the liquid phase would separate, fast at high temperatures, and that the solid phase, being low in moisture, would keep for some time. That was the origin of cheesemaking.
Once that was discovered, extracts of the abomasum were made by cutting pieces of fresh material and extracting it with warm (not hot) salt water, and the extract would also coagulate milk into whey and curds. This might be our first experiment in biotechnology, since people took a living thing, extracted the enzymes, and then used them elsewhere. Before the saltwater extraction was discovered, cheese was made with strips of abomasum put into the milk, and they were not always completely recovered!
These extracts were used for centuries, and only recently has modern science freed us from them. Most natural rennet comes from the veal industry, and since veal is not a huge item these days, the supply of natural rennet is quite limited. Now most chymosin is obtained by inserting the gene that expresses it into bacteria, sort of the 21st century comeback to the crude saltwater extractions. This has some important implications for vegetarians, since most cheese is made from milk with rennet from sources that do not have to do with the slaughter of animals. Although strict vegans do not eat cheese, many less strict vegetarians will eat milk products if they are not connected with the death of animals.
There is a natural vegetable rennet, from the thistle Cynara cardunculus. It is used in the Iberian peninsula to make sheep and goat cheese, and does a good job. It will also set cow’s milk, but is unsuitable because it produces a bitter products with cow’s milk.
I apologize for taking so long to explain rennet, but without it hardly any cheese could be made. Now, let us look at different kinds of cheese.
Cheese can be classified in many different ways. The simplest is just to look at moisture content, but cheeses of quite different properties may have similar moisture contents. I believe that a better was is to kind of classify them by how they are made (and aged, if aged). This kind of correlates with moisture content, but has the advantage of being able to sort out families of cheeses by process used to attain them.
Looking at it this way, the least highly processed cheeses are the fresh, firm cheeses like queso fresco that are made from milk that is taken near to the boil and treated with acid, usually vinegar or lemon juice, and stirring until the curds form. It is then put in a cheesecloth bag and drained for a few hours. That is it. It does not matter if the milk is raw or pasteurized, because of the high temperature step.
From here on, we shall assume that pasteurized milk is used. After cooling, bacterial cultures and rennet are added, the proportions depending on what kind of cheese is desired. If milk is used, after cutting the curds, cottage cheese results. If cream is used, cream cheese is the result after the curds are pressed together. Goat cheese is also made this was. Like queso fresco, these cheeses are unaged and quite perishable, so they have to be kept cold to keep for any length of time. These cheeses retain most if not all of they whey, so they are quite high in moisture.
Most cheeses are made my cutting the curd and draining they whey from it. This automatically makes them lower in moisture, since the whey contains most of the moisture. The whey is generally dried and used to boost protein content of other foods, but authentic ricotta is made from the whey, not the curds. To make ricotta, the whey is heated to near to boil to coagulate what protein is left (casein is resistant to coagulation by heating, but it is all in the curds now).
Now things get interesting. For soft cheeses, the curd is merely lifted from the whey and not pressed. The curd is salted, the amount of salt depending on the kind of cheese wanted. Here is where molds and bacteria (other than the starter bacteria) are added either to the outside of the molded mass of curd or blended into the curd. For soft cheeses like Camembert, the organisms are added to the outside of the curds where they form a “skin”. For “stinky” cheeses like Limburger the bacterium Brevibacterium linens is applied as a brine solution to the outside of the cheese. These cheeses are called washed rind cheeses because the brine solution is applied over and over to the surface, either during the entire aging period of just at the beginning. There is another bacterium, B. epidermidis, that is a close relative to the cheese curing one. This is the bacterium responsible for human body odor! If you take a chunk of Limburger and let it reach room temperature, you know what I mean.
For milder cheeses like Brie and Camembert, the rinds are washed with a culture of Penicillium camamberti. This gives a rind, but one of much milder flavor.
To make blue cheeses, like Stilton (one of my favorites) and Roquefort, one of several Penicillium molds are added. For Stilton, P. glacum is used, and the culture is mixed with the curds so that they develop inside the cheese as well as on the surface. For Roquefort, P. roqueforti is used, again mixed with the curd. By the way, Roquefort cheese can legally be manufactured only in the Roquefort region of France, and is always made with sheep’s milk.
To make pickled cheeses like feta, the curds are immersed in strong brine for the short aging period. There are no additional bacteria or molds added for those. For mozzarella and provolone, the curds are treated with warm water and kneeded. This kneeding aligns the protein chains and makes them stringy and stretchy. This is great for pizza and similar dishes, but never use mozzarella in sauces because the stringiness is a problem. By the way, authentic mozzarella cheese is made from the milk of water buffalo, herds of which were imported into Italy centuries ago just for this type of cheese.
To make the so called “Dutch” style cheeses like gouda, colby, edam, and jack, the curds are washed in warm water but not kneeded. These cheeses are lower in calcium and acid because of the water wash than most cheeses are. After the washing the curds are placed in molds and pressed to remove more whey and water. They are then aged for a short period.
So far, all of the cheeses are fairly high in moisture and are aged only briefly (if at all) because they are fairly perishable, ranging from very for cottage cheese to somewhat for Roquefort. They are best used shortly after purchase, but some of them will keep for a few weeks in the refrigerator.
The cheeses meant to be aged have a heat treatment after the curd is cut. For semihard cheeses like Tommes, the curd is heated to about 100 degrees F and then pressed gently to expel whey.
For cheeses like cheddar a more complex process is used. After the curd is heated to about 105 degrees F, it is piled up and then milled to expel whey and to reduce granularity. Then they are pressed fairly firmly to consolidate the curd, and aged for a longer period of time, usually months.
For cheeses like Asiago, the curds are heated to around 125 degrees F and pressed firmly. For Swiss, a culture of the bacterium Propionibacter shermanii is added after the curds cool and before pressing. Swiss requires a fairly high aging temperature, around 75 degrees F, where most other cheeses are aged at closer to 50. After weeks, the bacteria digest some of the lactic acid from the starter cultures and convert it to other acids and carbon dioxide. That is why Swiss has holes in it. By the way, a close cousin to that bacterium lives on our skin, and P. acnes causes trouble in some folks by digesting oils on skin.
For hard cheeses like romano or Parmesan, the curds are heated to around 135 degrees F and pressed very firmly. These cheeses are aged for often up to a year, sometimes more, and keep very well because of the low moisture content.
Cheeses made by similar processes often have less than subtle differences because of the nature of the milk used to make them. In the US, where most cheese is made on a huge scale with pretty much standard milk, a fairly standard product is obtained. However, let us take cheddar as an example. Mild cheddar is made with a starter that is more rennet than lactic bacteria, and has low residual acidity. Sharp cheddar is made with more lactic bacteria than for mild, and so has higher acidity after aging.
There is no accounting for taste when choosing cheese, but regardless of what kind you like, there are a few things to know to keep the cheese at its peak after purchase. First is buying the cheese itself. Most people go to the supermarket or big box store for their cheese, but having it custom cut by a cheese shop is the better way. The reason is surface area. In a cheese shop, the cheese is in a big block so light and oxygen do not affect it as much as precut slabs. If you do buy precut cheese, get the largest blocks that you will use before it goes bad. Unless you are going to make that pizza in the next day or two, never buy pregrated cheese because the surface area is so large that it goes stale rapidly.
The refrigerator is about the only choice for most people for storing cheese, but that is really too cold. Storage at about 60 degrees F in very high humidity is ideal, and the refrigerator is around 38 degrees and the humidity is usually near zero. Tight plastic wrapping is also bad, but at refrigerator humidity is just about essential. Ideally, a real cheese lover has a special cooler for it where the cheese can be left uncovered on a stainless steel rack so it can breathe and yet not dry out. Those do not come cheap.
Cheese, like butter, is quite prone to pick up odors, so keep your refrigerator very clean. Only a day or two in a smelly refrigerator can ruin cheese, even in plastic wraps. When handling cheese, try not to touch the part not to be served to keep from innoculating it with undesirable bacteria and mold. Never serve cheese straight out of the refrigerator, but rather allow it to come to room temperature under an inverted bowl to keep it from drying out. The full flavor is developed as it warms.
When making cheese sauces or chowders, add the cheese as near to the end of cooking as possible and stir as little as possible after adding it. The more that you stir, the more you align the long casein molecules and the stringer the product will be. Never use mozzarella for a sauce because you are guaranteed to have a string one.
Finally, something has to be said about processed cheese food, like American cheese slices and Velveeta. They actually have their place, but I do not consider them to be actual cheese. Neither does the government, because they have to be called processed cheese food. These are made by taking actual cheese scraps, usually from a mix of ripened, partially ripened, and new cheeses, mixing in a blend of citric acid and phosphates, then heating and blending them before injecting the mix into the bag and cooling it. It melts nicely without getting stringy so is fine on hamburgers and such, and makes a really good dip. It also keeps better than genuine cheese, so is sort of handy to keep for when you realize that the block of cheddar that you were going to use has gone moldy.
Well, that does it for cheese for tonight. Next week we shall finish up about milk by disusing the benefits of breast milk for infants.
Well, you have done it again! You have wasted many more einsteins of perfectly good photons by reading this cheesy piece. And even though Rick Santorum realizes he will NEVER be president when he reads me say it, I always learn much more than I could possibly hope to teach by writing this series, so keep those questions, comments, corrections, and other feedback coming. Tips and recs are also always welcome. I shall hand around tonight as long as comments warrant, and shall return around 9:00 PM Eastern tomorrow for Review Time.
Doc, aka Dr. David W. Smith
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