Flavor Basics

The flavor of cheese in influenced by many things -- microorganisms, enzymes, and processing steps to name a few. We'll take a look at the most basic reactions in this post.

Flavor

Why do we eat cheese? For its texture? For its powers of seduction? With reasons aplenty most would say for its flavor. What is flavor? Taste + Aroma. Our brain combines the information from our tongue with the information from our nose and the result is flavor. Cheese represents one of the most complex food products whose wildly different forms fall under the same moniker. Ceteris paribus, no sane person would think that fresh chèvre and aged Gouda were the same type of food based purely on flavor.

This post aims to address some of the underlying processes in cheese responsible for its unique flavors. I have a habit of saying “we’ll cover that in a future post”. That motto applies here more than ever. The biochemical process occurring in cheese are very complex. There are whole books written about how flavor is formed in cheese. For our purposes, we’ll introduce some of the main concepts. Rest assured, we’ll cover the really complex stuff soon enough.

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Acid Formation

One of the major processes occurring in almost all cheeses (those that are ripened) is the breakdown of lactose into lactic acid. This process has tremendous effects on flavor (and not to mention texture). Lactose is a sugar made up of a glucose molecule and galactose molecule. The starter culture break up the lactose and eat the glucose and turn it into lactic acid. This concept was introduced in a previous post.

Acid formation lowers the pH of the cheese and often correlates to an acidic/sour/tart flavor in cheese. Think of really old cheddar, it is really acidic or "sharp".

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Lipolysis

Most of the fat (aka lipids) found in milk/cheese is originally in the form of a triglyceride. There are three long chains called fatty acids, connected to a glycerol molecule. What's important here is that when those intact chains are connected, we don't taste much. Those chains have to be clipped off and/or broken down to start generating flavors and aromas.

Enzymes called lipases clip off those fatty acids, and they become free fatty acids. This process is called lipolysis. These fatty acids now have taste and aroma, yay! A really short fatty acid is called butyric acid and that is the hallmark of so-called "rancid" flavor, which is found in cheeses like provolone and feta. A not-so-consumer-friendly term for this is “baby vomit” aroma. Medium length fatty acids are partly responsible for goat-like flavor found in goat cheeses. Longer fatty acids taste soapy, so think of cheeses like Romano. Length of these fatty acids determine their flavor/aroma as you can see. Do you see how I drastically oversimplified things and attributed flavors to a single class of compounds? In reality it’s much more complicated and not completely understood.

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Proteolysis

Cheese, as mentioned in other posts, is made up of mostly casein protein. All that protein can breakdown into other compounds that generate flavor. Proteolysis is a catch-all term used to describe reactions involving protein breakdown.

Residual rennet could break off big chunks of the casein, and form what we call peptides. Peptides are shorter protein molecules. Some of these peptides can cause bitterness. From there, those peptides could be broken down even more by enzymes from the milk/starter cultures/NSLAB/mold/etc. into amino acids. Amino acids are the building blocks of proteins. These amino acids themselves are flavorful in some cases, but could also go on to react and form a whole bunch of flavorful compounds. See the last section of this post for a teaser.

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Secondary Reactions and Beyond...

We discussed the first stages of lipolysis and proteolysis above. Free fatty acid are formed from lipolysis. Peptides and amino acids are formed from proteolysis. These compounds certainly to contribute to flavor. But the story doesn’t end there. The products of these reaction can go on and form other flavor compounds. The exact processes can get quite complex, but one major pathway is through microbial metabolism. The bacteria/mold/yeast/etc. transform these compounds into different ones creating a huge assortment of flavor compounds. We’ll mention a few.

Beyond Lipolysis

Free fatty acids can further react to form thousands of flavor compounds. Buttery flavors, fruity flavors, perfumy, and many more are formed. Fatty acids can be converted to ketone and alcohol compounds by blue mold giving the characteristic medicinal aroma of strong bleu cheese.

Beyond Proteolysis

Oftentimes the amino acids left over from proteolysis go on and form many different flavor compounds. Sulfur containing amino acids can be broken down and eventually go on to form sulfur compounds, like you'd fine in some aged cheddars. Some protein break-down products could go on to react and form things like ammonia, like in Camembert (simplification). Break-down products can react with fat break-down products and give even more flavor.

For More Information

• Flavour Compounds in Cheese (Review)
• Biochemistry of cheese ripening
• Interactive Cheese Flavor Wheel