Breed & Season

The previous pages compared species. This one asks a narrower question with a bigger practical payoff: how much do the numbers move inside one species?

More than I expected. And once again, the lever is casein.

⭐ The κ-casein genotype — a 2.2-point swing in cheese yield

This is the single best fact in this wing, and it closes the argument the other pages have been building.

κ-casein — the protein rennet cuts — comes in variants. Cows carry AA, AB or BB. Measured cheese yields by genotype:

κ-casein genotype	Cheese yield
AA	11.64%
AB	13.3%
BB	13.8%

A 2.2-percentage-point spread between AA and BB — same species, same feed, same make. The B variant shortens coagulation time, improves curd quality and raises yield; BB cows give milk that clots faster and yields most.

Which is the whole wing in one table. Species differences, breed differences, and donkey milk’s outright failure all come back to which caseins, in what proportion, and not to fat or protein totals.

⚠ One honest caveat about that table: these are figures from breed-genotype research, and the cross-species yields came from a different meta-analysis with its own definition of “fresh-cheese yield.” So do not read “AA = 11.64%, goat = 11.9%” as meaning an AA Holstein is worse than a goat. Within each study the comparisons hold; across studies they don’t. It’s the kind of number-splicing that produces confident nonsense, and I’d rather flag it than quietly do it.

Which breeds carry it

Brown Swiss are reported at roughly 35% BB globally — the highest of the common dairy breeds, and the reason the breed has a cheesemaking reputation that isn’t just folklore. Its Italian counterpart is the traditional breed behind the great northern-Italian wheels.

Jerseys: North American Jerseys have a significantly higher share of BB than Holsteins do.

Holsteins, bred hard for volume, sit lowest — which is the trade-off written into the world’s dominant dairy breed. Enormous quantities of milk, less well suited per litre to cheese.

On A2: Guernsey, Jersey and Brown Swiss carry the A2 β-casein variant more frequently than Holstein and Ayrshire. A2 is a β-casein variant and is mostly discussed for digestion rather than cheesemaking — κ-casein is the one that moves your yield. Worth separating, because the marketing around A2 milk tends to blur them.

Practical upshot: if you can choose, milk from a Jersey, Guernsey or Brown Swiss herd is genuinely better cheese milk than Holstein milk — higher fat and protein, and better odds on the κ-casein. If you buy from a farm, it is a fair question to ask what they milk.

Season

The other variable, and it moves things you can see.

Colour. Green forage carries beta-carotene, which passes into the fat. Summer pasture milk makes noticeably yellower cheese than winter hay-and-silage milk. That’s why alpine wheels from mountain pasture are deep gold, why annatto exists, and — running the logic backwards — why buffalo mozzarella is pure white.

Solids rise as lactation advances. In sheep this is well documented and dramatic: through lactation, yield falls while fat, protein and total solids climb, so potential cheese yield goes up as volume comes down. Late-lactation milk is the richest of the year.

Heat cuts it back. Late-summer milk suffers from hot weather and poorer pasture — a real dip, not a folk belief.

And that’s why traditional cheeses are seasonal. Pecorino Romano’s PDO window and the winter/summer split among alpine cheeses aren’t heritage decoration; they follow the milk. The single most useful thing this page can tell a home cheesemaker is that the same recipe in June and in October is not working with the same material.

What to do about it

Keep notes on the milk, not just the make. Date, source, and — if you know it — season and breed. Otherwise a difference between two batches of the same recipe is unattributable, and you’ll blame your technique for something the milk did. This is the same argument as the make sheet, extended one step upstream.

Expect a lower yield from Holstein bulk milk than the books promise, and don’t read it as a fault in your make.

Don’t chase the season for its own sake — you can’t control your supply, and a good cheese from December milk beats no cheese in May. But when a wheel comes out unusually well, look at when before crediting yourself.

I have never had a choice of breed. My first cheese was raw milk from the farm down the road, and what the farm milked is what I got. That’s most home cheesemakers’ situation, which is precisely why it’s worth knowing what the variable is doing to you.

Next: raw vs pasteurized — the last decision in this wing, and the one with a legal answer as well as a technical one.

Sources

Cheese yield by κ-casein genotype (AA 11.64%, AB 13.3%, BB 13.8%), the B variant’s favourable effect on coagulation time, curd quality and yield, Brown Swiss ~35% BB globally, and North American Jerseys higher %BB than Holsteins: Swissgenetics, “Understanding kappa-casein BB”, Farming Connect, “The role of kappa-casein in cheese making” and The Bullvine, “Breeding for Kappa Casein to Increase Cheese Yield”
A2 β-casein more frequent in Guernsey, Jersey and Brown Swiss than Holstein and Ayrshire: Lactanet, “Selection for Milk Caseins: Beta and Kappa”
Breed comparison in a real make (Italian Brown vs Italian Friesian, high-moisture mozzarella): “New Insights in Cheese Yield Capacity of the Milk of Italian Brown and Italian Friesian Cattle,” Animals
Lactation-stage and seasonal effects on solids and potential cheese yield: “Impact of seasonal changes in ovine milk on composition and yield of a hard-pressed cheese,” PubMed