Flocculation.
Isn’t that a great word? I love a great word like that. Flocc-u-lation. Flo-cc-u-la-tion. It’s always one to raise an eyebrow. Either folks think you’re being dirty. Or that you’re trying to sound all high and mighty. Or, coming closer to the truth of things, that you’re a big dork.
But understanding flocculation is an important trick for any cheesemaker to have up their sleeve.
Flocculation doesn’t settle the question of who cut the cheese, but it will answer when to cut the cheese. It’s relatively easy to do (there is a bit of math involved), free, and could potentially save you from wasting your time over a milk vat that won’t coagulate or a recipe that won’t give you the results you’re looking for.
What is Flocculation?
So, what is flocculation? It is the point at which enzymes in rennet work their magic and begin to coagulate the milk. Simple as. More specifically the casein proteins are aggregating to form calcium bonds and result in a mass of curd. It happens very quickly, is visibly and physically discernible, and is a far more accurate test for when the curds should be cut than going by a “clean break.” A clean break can be tested for quite a while before the edges of the curd start pooling whey and getting jagged cuts. By that time, you’ve likely locked in way more moisture than you want and will end up with bitter cheese.
When you pinpoint how fast the protein and calcium bonds are forming, you can calculate the rate at which the curd will be ready to cut.
Want to geek out even harder? Check out this article on the science behind coagulation. It’s surprisingly accessible!
Factors that Affect Coagulation Time
How long does it take for milk to reach the flocculation point after adding the rennet? It depends. (Couldn’t be an easy answer, now could it?) Factors that affect it include how much rennet you use in the recipe, the temperature of your milk, as well as the components, freshness, and acidity of your milk. Typically, it takes between 10-30 minutes. As the coagulation progresses, the curd will get continually more firm.
Moisture is locked into the curd as the protein bonds become stronger. The longer you allow the milk to coagulate, the more moisture will be trapped in the curd. So if you are trying to make a hard alpine cheese, such as parmesan, you want to work with a very short coagulation time. For a moist, creamy cheese opt for a longer coagulation.
Factors that affect total coagulation time include:
Old or weak rennet will take longer to set curds than your recipe may call for. (If you’re not sure you can test batch your rennet using a gallon of milk instead of a full pot. Be sure to adjust the ratio of rennet to match a familiar recipe.)
Likewise, using old or weak cultures will affect the acidity of the milk and, therefore, the length it takes to fully coagulate the curds.
Older milk or milk that wasn’t cooled quickly will have a higher acidity.
Increased protein in the animal’s diet will increase coagulation time (there are more proteins to bond.)
Perhaps you like a moist cheddar for this cheese or a dry one on another occasion. Simply adjust your total coagulation time.
Pasteurizing milk affects the protein in the milk and they will not coagulate predictably.
Using the flocculation point will help navigate those factors as well as allow you to influence your final cheese with more predictable results. Were you not checking your flocculation time and it happened more quickly than the recipe guideline, you allow too much moisture to get locked in and the final cheese may be sour. If it took longer to flocculate than the recipe anticipated then your cheese may end up too hard and dry.
How to Recognize the Flocculation Point
Though I prefer an easier, hands-off method, you can recognize the flocculation point with your hands by gently pressing a fingertip onto the surface of the milk and observing an impression made on the top. (As the coagulation progresses and the bonds more tightly lock, you can press with increasing pressure.) This is not the same as the cream layer rising to the top. You can break through the cream layer and feel the liquid milk beneath. When the milk has begun coagulating, it will happen in the fullness of the mass. At the flocculation point, were you to break into the mass, it will have the consistency of gravy.
Another way to check the flocculation point is to set a smooth-topped, plastic, vitamin bottle cap upside down onto the surface of the milk just after stirring in the rennet. It’s like a little boat on a milky lake. Be sure you sanitized and completely dried the cap before placing it on your milk. Set a timer and check your milk every five minutes if you don’t know what your target time is.
To check your milk for the flocculation point, gently flick the cap across the surface. At first, you’ll notice it glides like with the wind. When the magic moment gets close, you’ll notice the cap meets with resistance part-way through the glide. When your little boat is land-locked and flicking the cap meets with resistance right away, you have arrived.
Here is a video I made for Homesteaders of America using my cheddar cheese recipe. I add the rennet at :46 and demonstrate the flocculation test with the cap as well as what to look for when cutting the curd.
Flocculation Multipliers
Now, what do you do with this information? Well, sadly, the answer is some math. Grab your calculator and first figure out how long it took from the minute you added the rennet to the minute you noticed flocculation. Let’s say it was 10 minutes. Multiply that flocculation point number (Fp) by the multiplier (M) you’d like to use for the final moisture level in the cheese.
Parmesan & Alpine cheeses- 1-2 (Some use a very low flocculation point for these. Merryl Winstein uses .167 but I couldn’t even crack my 6-gallon Winstein parm aged for 10 months. So, in my experience, that multiplier is far too short and dry for a small batch cheese and you might have a brick that tastes like parm but you’ll never know because you can’t hack into it. Even with a cleaver. Other sources generally seem to fall between 1 and 2. I can neither confirm nor deny. If I ever end up with a parm recipe that is any good, I’ll be sure to let you have it.)
Dry, aged cheeses- 2-2.5
Moist, aged cheeses- 3 to 3.5
Feta- 4
Brie-style- 4-5 (I do less if I plan on baking the brie, more if I want it to be runny when cut.)
Since we are dreaming of a nice, grilled burger topped with a slice of melting cheddar oozing over the edges on this cloudy winter day, we want it a little moister and will use a multiplier of 3. Our total coagulation time then is 30 minutes.
BUT we’ve already gone through ten minutes of coagulation time so that must be subtracted. Set your timer again. We’ve got 20 more minutes until it’s time to cut the curds.
Fp(M)= Total Coagulation Time
10(3)=30 minutes
Fp(M) - Fp = Time Remaining
30-10= 20 minutes
Checking for Curd Set
With the exception of parmesan/alpine cheese where you want very little moisture to be locked in, most cheeses will have a very firm top that gives you that clean break recipes call for. If you press the curd mass downwards with the palm of your hand, you’ll feel resistance and it will pull away from the side of the pot. (For alpine cheese the curd mass will be much softer. It reminds me of the texture of yogurt. For brie-style cheeses, where you want a lot of moisture locked in, the curd should be very firm with some whey beginning to puddle around the edges of the pot or top of the curd mass.)
Finally, I think it’s worth mentioning there is, unfortunately, some confusing language about the correct way to calculate the total flocculation time. Some authors indicate that the product is the TOTAL coagulating time (rennet to cutting) so it would stand to reason you’d subtract the flocculation time that has already passed from the total time. Other authors state that the product is ADDITIONAL time.
“If using flocculation as a guide, multiply the time to flocculation by 2 to 2.5 for the total time from adding rennet to cutting.” (emphasis mine) Mastering Artisan Cheesemaking, Gianaclis Caldwell
“For example, you’ll cut an Asiago cheese at three times the flocculation point because it is a drier cheese, whereas you’ll cut Brie at six times the flocculation point.” Kitchen Creamery, Louella Hill
“You can now determine the flocculation time to be the minutes since you added the rennet. To estimate when gel development will be complete, multiply the flocculation time by the rate factor. For example: If it took 10 minutes for the onset of flocculation and the rate factor is 3, the gel would be ready to process 30 minutes (3x10) from the time the rennet was added.” The Complete Idiot’s Guide to Cheesemaking, James. R. Leverentz
“If you are trying to make a soft cheese and you observe that it takes 10 minutes for the milk to flocculate, you will need to let the coagulum rest for another 20 minutes (2 x10). The total coagulation time with the addition of the coagulant and the cutting time should be approximately 30 minutes. (20 times for the resting time and 10 minutes for the flocculation time.)” The Joy of Cheesemaking, Jody M. Farnham
“The time from adding rennet to the first sign of flocculation is then multiplied by a mathematical factor to calculate the cutting time. This approach is based on what appears to be a reasonable sound assumption, that the optimum cutting time is proportional to the flocculation time; the longer the milk takes to flocculate, the longer the time to optimum cutting firmness. Thus if flocculation occurs at 10 minutes after the rennet is added in Cheddar cheesemaking, the recommended cutting time is 10 x 2.5, or 25 minutes.” American Farmstead Cheese, Paul Kindsteat
Merryl Winstein in Successful Cheesemaking says to “Multiply the flocculation time… add that amount of time on.”
Gavin Weber’s video on flocculation does not address this issue directly, however in the comments, when asked which way, he states simply, “It’s the total time.”
It’s frustrating there isn’t a general consensus on this because in the case of a 10-minute flocculation with a multiplier of 3, you’re talking about the difference between a total time of 30 minutes versus a total time of 40 minutes. This is why it is so important to take notes when sampling new recipes or developing your own. And why it’s so important to learn how to use flocculation as a tool in your cheesemaking. If you find when you use the total coagulating time method and your cheese turns out too dry, you can either increase your multiplier for a moister cheese or switch to the additional time method. Personally, I’ve had great success with my cheese using the total time so that’s what I’m sticking with.