This Wiki Article discusses the different methods to determine when to break or cut the milk curd after it has been coagulated, a critical control point in making cheese. When milk first coagulates, it has a natural tendency to contract and expel whey. This property is called syneresis and it depends on several factors, the largest being surface area of the coagulum or curd. Initially the milk is coagulated as a single large curd with a small ratio of surface area to volume which results in slower and less whey expulsion from the coagulum as the whey in the middle has a long distance to travel before being free from the curd.
The purpose of breaking (for lactic acid coagulated cheese) or cutting (for rennet coagulated cheese) the curd is to increase its surface area to volume ratio and thereby increase its expulsion of whey to reduce the water content of the curd and in the final cheese.
Lactic Acid Coagulated Cheeses
Lactic acid coagulated (i.e. no or minimal rennet) cheeses such as cream cheese and cottage cheese are normally formed as one large curd and broken either by stirring or ladling.
This should be done when the coagulum reaches a pH of 4.6-4.7, more acidic - lower pH and the curd will be brittle and “shatter”, higher pH and the curd is more rubbery and clumps together.
If not using a pH meter, a pH of 4.6-4.7 is normally reached when the curd either pulls away from the sides of the vat with about 1 cm/0.5 in of whey around the perimeter and on top of the curd or the curd tears in the middle with about 1 cm/0.5 in with whey released in the gap and again on top of the curd, click on pictures to enlarge and view.
Rennet Coagulated Cheeses
Cutting of rennet coagulated curds should happen when the curd is firm enough to cut cleanly:
- If cut too early then the curd be mushy and cut poorly into non-ideal uneven small pieces or fines resulting in 1) fat and casein loss to the whey and thus poor yield, and 2) lower moisture content in the cheese.
- If cut too late the curd will be very firm, tough, rubbery and will bunch up around the curd knife when cutting and i) tear into pieces of non-preferred uneven size, and ii) tend to resist whey expulsion and result in higher moisture content than wanted in your cheese. Additionally, the un-cut curd will already be expelling whey from its surface and shrinking resulting in uneven density cut curds, as dryer at surface and moister cut curds from interior.
The following are three common methods for determining when to cut rennet coagulated curds, from simple to accurate:
Method #1: Timing
This method simply involves using a set time after rennet is added, i.e. 20, 30, 45, 60 minutes to cut the curd.
While simpler for authors of cheese making recipe books, this method is not recommended as milk types and starter cultures vary widely around the world and across the season thus a non-optimal time of cutting is highly probable.
Method #2: Clean Break
This method involves inserting a clean finger or flat object into the curd at a ~45 degree angle to a depth of 5 cm/2 inches at an early time point, i.e. 20 minutes after renneting, and then lifting the finger or spatula or knife vertically to break the curd. You then observe the curd to see if in general:
- You have a sharp clean split of the curd and green whey accumulating in the pocket where the cut was made, in which case the curd is ready to be cut.
- You have a ragged mushy split with milky whey accumulating in the pocket where the cut was made, in which case the curd is not yet ready to be cut and more time, say another 10 minutes given for the curd to set before trying the test again.
This method isn’t perfect as the ideal firmness of the curd is a function of the milk, which varies over the season, and the cheese type being made. Note, some cheese making procedures call for varying level of firmness before cutting, for example Roquefort using sheep’s milk calls for firmer curd before cutting than blue cheeses using cow’s milk.
Method #3: Flocculation Point
This method is the most complex and the most accurate. For this you need to observe the onset of flocculation which usually occurs ~10-15 minutes after adding rennet. This time after adding rennet to the onset of flocculation is then multiplied by a factor, dependent on the cheese type being made, which determines when to cut the curd after the addition of rennet. This method is based on the optimum cutting time being proportional to the flocculation time and that there are two phases in curd formation. First is the enzymatic phase followed by the aggregation phase where the lattice or curd is formed. The flocculation time is at the start of the aggregation phase. These times are dependent on the levels of casein and calcium which vary with the source of the milk, thus this method takes into account the milking/lactation cycle through the year.
The factor applied to the flocculation time is a function of the cheese type being made, normally between 2 and 6, for example 2-2.5 for Swiss & Alpine types, 2.5-3 for cow’s milk Cheddar, 3.5 for Monterey jack, 4 for Feta & Blues, and 5-6 for soft cheeses such as Camembert & Domiati. So if flocculation time is 15 minutes, then for Feta or Blues, total time since adding rennet to when cut is 60 minutes.
The reason for the different multipliers for different cheese type recipes – procedures is because the curd at time of cutting will have different strength, young curd set will more readily release water when cut versus older curd set will release less. Thus this time, along with the cut curd size are large determinants in the final moisture content of the cheese.
Note, many aged goat cheeses are made from a hybrid lactic and rennet curd set, time to cut is usually performed when pH has dropped to 4.5 and cutting is performed by ladling the curds into forms.
Optical Flocculation Time Test:
This test uses visual observation of the flocculation of the milk and is normally used by very experienced cheese makers.
- When adding rennet to milk start a timer.
- Insert a metal spatula into the milk, withdraw it and observe the milk as it flows back off the spatula, it will drain freely.
- After the milk has pre-ripened for ~8-10 minutes, repeat every ~30 seconds. Initially the milk will thicken and then at the onset of flocculation at the surface of the milk, tiny white grains will be seen in the film of the milk off the spatula. That is your flocculation time.
Physical Flocculation Time Test:
This test uses a physical observation of the flocculation of the milk and is better for less experienced cheese makers.
- When adding rennet to milk start a timer.
- Float a small bowl on top of your milk, spin the bowl, it will spin freely because the milk has not flocculated.
- After the milk has pre-ripened for ~8-10 minutes, spin the bowl every ~30 seconds. When the bowl won’t spin, that is the flocculation time.
Flocculation time multipliers: