How Much Cream Will You Get? Working Out Separation Yield
"How much cream will this give me" is one of the first questions a small dairy asks, and one of the few that can be answered before the machine is bought. It is arithmetic on three numbers rather than a performance claim, and it is worth doing on paper because it tells you whether your batch size and your machine are matched.
The three numbers that decide the answer
- Volume of milk. Measured, not estimated from the size of the churn.
- Fat content of that milk. From a test, or from the record of the farm supplying it.
- Fat content you want in the cream. This is the setting you choose, and it is close to what the cream-screw position controls.
A fourth number, the fat left behind in the skim, is a result rather than an input. The examples below assume 0.05 percent, which is a normal figure for a separator that is working properly. If you have your own test result, use it instead - the arithmetic does not change, only the outcome.
The calculation
Separation conserves fat. Whatever was in the milk leaves through one of the two outlets, so the fat in the cream plus the fat in the skim equals the fat in the milk. Rearranged:
cream = milk x (milk fat - skim fat) / (cream fat - skim fat)
All quantities in the same unit - if the milk is measured in litres, treat one litre as one kilogram. The error from doing so is small and it does not change any decision you would make from the result.
Worked figures
For 100 kg of milk at 4.0 percent fat, with skim assumed at 0.05 percent:
| Cream fat wanted | Cream produced | Skim produced | Milk to cream |
|---|---|---|---|
| 35 percent | 11.3 kg | 88.7 kg | about 9 to 1 |
| 40 percent | 9.9 kg | 90.1 kg | about 10 to 1 |
| 45 percent | 8.8 kg | 91.2 kg | about 11 to 1 |
| 50 percent | 7.9 kg | 92.1 kg | about 13 to 1 |
Two things follow from the table, and both surprise people who have not run the numbers. Thicker cream does not mean more cream: the fat is identical, it is only more concentrated, so a higher target reduces the weight you collect. And the ratio between milk and cream is a property of the milk and the setting, not of the price of the machine.
Why your own figure will differ
The calculation is exact; the inputs are not. Four things move the real number away from the table:
1. Fat content of the milk changed. Feed, stage of lactation and season all move it, and a batch that tested 4.0 percent last month may not be 4.0 percent today. This is the largest single source of error in the estimate.
2. The skim is not as lean as assumed. If the feed rate is too high, the milk is too cold, or the disc stack is not seated correctly, fat leaves with the skim and the cream yield drops. The loss is invisible unless the skim is tested or tasted for richness.
3. Cream is left in the machine. Whatever remains in the bowl at shutdown is not in your container. Consistent shutdown practice makes this a constant rather than a variable.
4. Foam and spillage. Cream that foams out of the outlet is lost twice - once as product and once as cleaning time.
How to check your own numbers in three runs
You do not need a laboratory to get useful figures. Weigh the cream container empty, weigh it again after the run, and write down the milk volume and the cream weight side by side. Do it for three runs at the same setting. If the three ratios agree within a few percent, your process is repeatable and the table above is a reasonable planning tool. If they scatter, the cause is one of the four items above, and the consistency guide covers how to find which one moved.
A fat test on the milk, if you can get one, improves the estimate far more than any other single measurement.
What this means for capacity
Working backwards is the useful direction. If you need a given weight of cream per week, divide it by the ratio in the table to get the milk volume, then divide by your available session hours to get the flow rate you need. That number, compared with the rated throughput on the machine, tells you whether one session covers your week or whether you are planning two.
Be careful at this step: a rated rate is not a working rate. Setup, filling, the slower pass at the end of a batch and cleaning all sit outside the rated figure. The real throughput guide sets out what moves that number, and the capacity selection guide covers matching a machine to a working day rather than to a datasheet.
What this page does not tell you
It does not tell you what the cream is worth, what your fat recovery should be, or how the machine will behave on milk that is colder or older than usual. It is a planning calculation, not a specification of performance, and it should be replaced by your own measured figures as soon as you have three of them. Our product pages state rated throughput for each build; the arithmetic above is the step that turns a rated figure into an expectation for your own batch.
Related maintenance resources
Use the ANDUUK replacement parts catalog to match seals, discs, outlets, motor components and cleaning tools to the correct machine assembly.
Browse replacement parts · Read the cleaning and reassembly checklist · Read separator FAQs