It’s a question that gets asked time-and-time again, why is Cheddar cheese bitter?
Perhaps, you’ve even noticed this yourself.
Then again, maybe you find that certain cheddars seem fine, whereas others have a bitter taste.
So, what exactly is going on here?
Allow me to explain about cheddar cheese and potential bitterness.
There are actually a number of reasons that cheddar cheese is bitter. The most obvious of these is due to the age of the cheddar. The bitterness comes from the peptides that form during the aging process. Therefore, a mature cheddar is likely to taste more bitter than a mild cheddar. Additionally, rennet is used during the cheese-making process, and this is occasionally animal rennet. However, as vegetable rennet is more commonly used, this can impart a more bitter flavor.
1. Why Is an Aged Cheddar More Bitter?
It’s true, not all cheddars are created equal.
And therefore, you’ll typically notice that some cheddars are more bitter than others.
This typically comes down to the age of cheddar cheese.
Basically, during the aging process of cheddar, and for all cheeses for that matter, bioactive peptides will be produced.
So, the older a cheese is, the more peptides that will form.
And it is these peptides that typically make a cheese sharp or bitter.
Therefore, you’ll generally find that a mild cheddar, which has only been aged for a few months, is likely to taste much smoother
However, a mature cheddar, which may have been aged for a number of years, will typically taste bitter.
2. Can Rennet Make Cheddar Bitter?
Something else to consider is the use of rennet is cheese-making.
Rennet is an enzyme that is used to curdle the casein in milk, which in turn will separate the curds and whey.
This is the initial process used when it comes to making cheese.
Now, rennet has always traditionally been extracted from the stomachs of calves.
Basically, the inner chamber of the fourth stomach is removed and then sliced into small pieces.
These pieces are then placed into whey or salt water, and then vinegar or lime is added in order to reduce the pH of the overall solution.
You may initially believe that this would make the solution bitter, but it doesn’t.
With that being said, it is estimated that only around 5% of all cheese produced in the world now uses animal rennet.
Therefore, the majority of rennet is now produced from plants, such as nettles and thistles, or from other bacterial sources.
You’ll typically find that vegetable rennet gets more bitter as it ages, typically after 6 months or more.
Whereas, animal rennet will not get bitter.
But, when you consider that the vast majority of cheddar (and cheeses) now use vegetable rennet, it’s easy to see why the finished product may taste bitter.
Easy Cheese Making With Rennet
3. Can “Undesirable Organisms” Make Cheddar Bitter?
If you’ve researched online the reason why cheddar cheese is bitter, you’ll typically be greeted with information about “undesirable organisms”.
However, in truth, this doesn’t strictly refer to the cheddar cheese you purchase at the store or the supermarket.
Well, you’d hope not anyway.
In fact, this is far more geared to those who actually make and produce their own cheddar cheese.
So, undesirable organisms are something to look out for if you make cheese at home for your own consumption.
Basically, this refers to perhaps obtaining inferior quality milk, typically alkaline-forming and protein-splitting bacteria.
This is often the case if the milk was collected from dirty cows.
Then again, this could be due to using old starter bacteria, and even from rusty or unclean milk cans.
So, as I say, this is not something that you’d typically have to worry about from store bought cheddar.
However, if you are making your own cheese, any one of these things can cause your cheddar to taste bitter.

Final Thoughts
So, I hope you understand that there are a wide variety of reasons why cheddar cheese is bitter.
The most obvious of these will be to do with age.
Basically, the older (mature) a cheddar is, the more peptides will form, which will impart a more bitter taste.
With that being said, rennet is used in the cheese-making process.
This was traditionally done using animal rennet.
However, in the modern day and age vegetable rennet is much more commonly used.
And vegetable rennet is definitely more bitter (especially when aged) than the animal variety.
Finally, if you’re actually producing your own cheddar, or have even gone directly to a farm, the bitter taste could be down to undesirable organisms.
Talking of unwanted stuff, what happens if you don’t refrigerate Cheddar cheese?