I know most people probably don’t like to think of food and taste in terms of chemicals and receptors, but that’s really all that’s going on when we’re talking about taste and smell. And man, little microbes are awesome for making these compounds for us. Thanks, little guys!
Today I would like to discuss diacetyls. What is a diacetyl? It’s this:
But it’s so much more than that little figure. Diacetyl is, in short, butter. It’s responsible for buttery flavor. In fact, pure diacetyl is the “fake” butter that they add to popcorn in movie theaters. If you are tasting butter flavor in your cheese, it’s a result of this little compound hanging around. The same goes if you’re drinking chardonnay or beer with some buttery over/undertones. It’s a versatile little guy.
Speaking of butter flavor in cheese, have you tried St. Angel from Guilloteau? I swear, I don’t want to promote specific cheeses or one cheese over another – but I have to physically restrain myself from buying it sometimes. It’s like BUTTER CHEESE. I promise my love for it has nothing to do with my name. You should try it. If you put way more butter on your bread than you should and you love cheese, this little guy was made for you.
Anyway, back to diacetyl. How is it made in our cheese?
First, let’s recall lactic acid fermentation. Typical starter cultures we use contain two species of L. lactis that produce lactate (lactic acid) from glucose. I’ve highlighted that section here:
Some cultures – particularly those that are used to make butter and the one I used to make Baby Brie – have additional bacteria added. These guys are capable of converting pyruvate (a fermentation product) in to diacetyl:
L. lactis biovar diacetylactis is one of the bacteria species that produces diacetyls. They produce the buttery deliciousness with the help of the enzyme α-acetolactate synthase, which converts pyruvate to α-acetolactate. Once this product is formed, it will become decarboxylated in the presence of oxygen to make diacetyl. Yum!
In addition to the butter flavor, these little bugs also produce acetoin – which is the compound responsible for the smell of butter. Once α-acetolactate is formed, a second enzyme (α-acetolactate decarboxylase) converts it to acetoin. Both the production of diacetyl and acetoin result in the release of CO2, which results in tiny little holes in the cheese.
So there you have it. The flavor and smell of butter are the result of two compounds. It’s really quite astonishing to think that our experience of a food can be dictated by two such small little chemicals. That being said, it doesn’t change my love of butter (and butter cheese!) one bit.