The molecular secrets of cream cheese
The June issue of Wired Magazine carries a story about one of the two university labs in the U.S. dedicated to cream cheese research. This one is -- where else? -- in Madison, Wisconsin, where researchers are exploring the molecular mysteries of cream cheese. You may not know, but this cheese is tricky to produce because the acid-secreting bacteria used to coagulate the milk need to be killed at the right time. The researchers are now writing a guidebook about the secrets of cream cheese, book which will be available to anyone, in a process similar to the open source movement for software. But read more...
The title of the Wired article is "Schmear Campaign." If American English is not your mother tongue, like myself, you might wonder what is the meaning of "schmear." The nice editors of Wikipedia tell us what it means in this page about cream cheese. And of course, they also give us a definition of what is this cheese.
Cream cheese is a soft, mild-tasting, white cheese that contains at least 33% milk fat (as marketed) with a moisture content of not more than 55%, and a pH range of 4.4 to 4.9. It is sold in brick form or in a small, tub-like container. Variety brands add such additional seasonings as garlic, dill, and olives. Cream cheese differs from other cheese in that it is not allowed time to mature and is meant to be consumed fresh. It is a primary ingredient in cheesecake and other desserts, and is often spread on bagels and eaten with lox (smoked salmon). On bagels, cream cheese is sometimes referred to by the Yiddish word schmear.
And if you want to know what it looks like, below is a picture of cream cheese spread on a bagel (Credit: Renee Comet, National Cancer Institute, via the cookbook with cream cheese from Wikibooks).
Now, let's go back to the Wired article, which describes the efforts of Mercedes Brighenti to break the secrets of cream cheese. Brighenti works in the Wisconsin Center for Dairy Research of the Department of Food Science at the University of Wisconsin-Madison under the direction of John Lucey.
Here are some selected excerpts about the making of cream cheese.
Scientifically, it’s one of the trickier dairy products. In their natural state, the protein molecules in milk have a negative charge, so they repel one another – that’s what keeps milk liquid. To solidify it (that is, turn it into cheese), this repellency must be overcome. [...] Acid-secreting bacteria are added to the milk, and the decreasing pH flips the charge of some of the milk’s proteins. The positively charged molecules attract the negatively charged ones, coagulating the liquid and eventually turning it solid.
The key is getting the cheese to an isoelectric state – the point at which half of its proteins are positive and half negative. Left alone, the bacteria will continue producing acid, giving all the molecules a positive charge and turning the mixture back into a liquid. To stop the acidification, the cheese is heated until the bacteria dies. The cheese maker has to anticipate the isoelectric state and kill the bacteria at the right time.
And cheese makers have their own secret recipes to determine when it's the right time to kill the bacteria. This is what Brighenti and Lucey are about to change by writing "a sort of guidebook to the inner workings of cream cheese" which will be available to all cream cheese makers, including Kraft, which has about 70% of the whole market.
Strangely, there are not many academical papers about cream cheese. But Brighenti and Lucey, along with other researchers, have presented a paper named "Textural properties of commercial cream cheese" at the 2005 meeting of the Federation of Animal Science Societies. Here is a link to the abstract (PDF format, 2 pages, abstract on the right column of page one) from which I have extracted the following information.
There has only a limited amount of information published on the textural and rheological properties of cream cheese. Objective of this study were to characterize the textural properties of commercial cream cheese products. Nine types of commercial cream cheeses including full fat, (one-third) less fat and fat-free (one sample), were obtained from a local grocery store. [...] Texture properties were analyzed by penetration test. [...] The penetration test clearly indicated that full fat cream cheese had greater hardness (mean values ranged from 308 to 588g) compared to less fat (50 to 236g) or fat free (182g) cheeses.
If you've read this full note, you must be hungry by now. So it's time to go to your grocery store and buy some cream cheese for cooking a cheesecake.
Sources: Joshua Davis, Wired Magazine, Issue 14.06, June 2006; and various web sites
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