Oh Holey Swiss Cheese

When in Switzerland, my day begins with cheese; a trail lunch will be either cheese and crackers or a stop at a chalet for some fondue. During this last trip, I became attuned to the nuances in flavor, even within the same appellation d’origine contrôlée (AOC).

How does cheese get its taste?

My investigation began during a rainy day visit to La Maison du Gruyère My favorite part was sniffing the various alpine plants which alpine cows eat.

Finding #1. Flower-filled Pastures with a View of the Alps Make Tastier Milk than Grassy Plains
It seems obvious, but of course a bunch of scientists had to prove it: a cow eating a mix of alpine grasses and flowers produces milk with a different flavor profile than that of a cow eating a low-land pasture. A Swiss researcher quantified these differences and published the findings published in 1988 and 1991. (1)

Finding #2. Pasteurization Kills Bacteria and Flavor
Another flavor-maker is unpasteurized milk. In the U.S., we kill organisms and destroy helpful proteins eduring pasteurization and then have to add cultures back in. What is present naturally in milk is a much more complex flora than the mix used by U.S. producers.

Finding #3. The Ripening and Aging Process is Complex
It involves a number of variables:

• bacteria and enzymes of the milk (pasteurization kills the first and changes the second)
• lactic culture (I think at the Gruyere factory, they save some whey from the previous batch, but am not sure)
• rennet (this is a crazy ingredient – when they slaughter an unweaned calf for veal, they save the fourth stomach chamber and then dry, clean and slice it into small pieces with salt water, vinegar or whey to reduce the pH. They filter it and the liquid they take off of it contains a mix of enzymes which coagulate the milk. It makes me wonder:  how did they figure this out? – ‘hey Marge! maybe we should toss some of this stomach in to the cheese mix…’?).
• lipases present in the rennet (lipases break down fats)
• added molds or yeasts
• environmental contaminants

Each one of those agents holds a universe of possibilities for flavor tweaks.

Scientists have a general understanding of the aging process. For these longer-aged cheeses, the bacteria present in the starter inhibit the growth of harmful organisms. These bacteria also die off.  And when bacteria cells die their cell walls fall apart and release enzymes which are now free to break down the  fats and proteins within the cheese.

Fat or protein + enzyme -> flavors

With some cheeses these changes promote the growth of a different set of organisms which add their own waste products which manifest as holes, flavors, rinds, etc. The biochemical details of these processes are not entirely worked out.

I used to have a sourdough starter that I called, “The Beast.” The more I read about cheese, the more I see its production as a whole community of Beasts, the populations of which the cheese-maker tends and nurtures.

Finding #4. Holes are Good Except When they’re Not
If cheese from The Bernese Oberland has holes, they don’t sell it.
Here’s why. If Oberlander Käse has holes, it means the cheese got too warm during the first 10 days of aging in the alp house and a bacteria, probably Propionibacterium shermanii, has grown. In this case, the bacteria produces off flavors. (The cheese doesn’t stay in the alp house long. After those first 10 days of washing in a brine/bacteria mix, it is moved to a cellar on the side of the mountain where the temperature is 55-60F for a year or more.)

Cheese from the warmer region of Emmental, however, does have holes. Three different bacteria inhabit Emmentaler cheese: Streptococcus thermophillus, Lactobacillus and Propionibacterium freudenreichii. Though their names sound scary, the first two bacteria are familiar – they are both part of the “live cultures” in yogurt. They create lactic acid which is in turn eaten by that last bacteria, which people call “prop” for short. And when “prop” uses lactic acid, it releases CO2 which makes the holes (bubbles) in the cheese. Cool, huh?

Finding #5 They’re still discovering about cheese. For example, an article published in January 1996 in the International Journal of Systematic Bacteriology describes the discovery of 2 new bacteria that they found on the surface of Gruyére and Beaufort cheeses. (2) 
Considering the brining that happens during the aging process of Gruyeres, I wasn’t too surprised to find out that these two species are highly salt tolerant. They’d have to be.

That was when I really started to appreciate the complexity of organisms living in cheese.

And I hadn’t even gotten to the molds yet.

Finding #6. The white “bloom” on French cheeses such as Camembert and Brie comes from a mold Peniccillium camemberti.

Finding #7. Raclette requires a yeast for its flavor Yarrowia lipolytica. This yeast is very different from the yeast of brewing, etc. First of all, to live, this yeast requires oxygen (bread and beer yeast can use either O2 or CO2); but what’s really cool is that this yeast can actually use normal hydrocarbons and various fats as carbon sources. When I read that, I immediately thought: bioremediation? and yes – they are currently developing this organism for use in a wide variety of products and technologies.

That’s probably enough nerdy stuff on cheese for one day.

I still have about 0.5 kg of Raclette left from the trip. Now would be a great time for a snack.

For the Geeky Crickets out there:

(1) Sehovic, J. (1988) “Secondary metabolites in some plants of grassland forages.” Rech. Agron. Suisse. 27:  153-165.
Sehovic J. (1991) “Consideration on the chemical composition in the quality estimation of the natural grassland forages.” Rev. Suisse Agric. 23:  305-310.

(2) Schubert, K. et al. (1996) “Two coryneform bacteria isolated from the surface of French Gruyère and Beaufort cheeses are new species of the genus Brachybacterium: Brachybacterium alimentarium sp. nov. and Brachybacterium tyrofermentans sp. nov.” Int J Syst Bacteriol. 46 (1): 81-7.