The Mystery of the Non-setting Sheeps Curd

After a summer and early autumn feeling like I got to grips with making some pretty good cheeses, the late season milk has thrown me a curve ball.  A lot is talked about seasonality in rather hazy, romantic terms of the terroir and what grasses or herbs or clover is available during the summer versus hay or silage in the winter.  Or even slightly more scientifically in terms of levels of fats and proteins in late season milk.  Very little, in my experience, is talked about in terms of temperature.We have recently had a head spinning turnaround from milk that set quickly and firmly (which we put down to high solids) to milk that just isn’t setting.  Fats and proteins aren’t dramatically different from the fast setting curd milk, there may be a little less calcium in the milk due to the grass quality not being what it was but basically that doesn’t seem to be the key issue.  Temperature.

For starters, the milk that had been arriving in the dairy at 27C or more in fact earlier in the year is now about 18C or 19C.  There are less sheep milking as more of them are served and those that are milking give less and less milk.  The body temperature of each sheep and the temperature of milk coming from each sheep hasn’t changed, but other factors mean the milk is much colder.  The sheep are milked before the cows.  The pipework is cold in the mornings now as it’s autumn and in addition it’s dark when the milking starts so what sun or daylight there is has had no chance to raise the temperature of the air or surroundings.  The milking system works by accumulating about 8 litres milk in a jar and then pumping it through into the dairy.  However it now takes longer to accumulate the 8 litres allowing the milk longer to cool as it does so.  It’s then pumped through cold pipes into the dairy.

Then there’s the room temperature or really to put it more accurately, drafts and currents of cold air.  If you look at the thermometer in the room the temperature hasn’t dropped massively and the heaters are going full blast and turned up as high as they can be.  However in the corridor where we do the packing the temperature is quite a bit colder which means that at this time of year, doors need to be closed to preserve the temperature in the dairy.

In the past couple of weeks the milk has gone from setting a bit too quickly because of its solids to setting very very slowly. Thinking back, the last of our fast setting milk was also at a point when the days were a little longer and then there was the brief Indian Summer when everyone went to the beach in October.  As the weather broke, the setting problems begain.  In looking at why this is happening (largely to me but it has happened to Martin too) we’ve looked very closely at the different ways in which temperature affects what we’re doing and how without us actually changing what we do, the parameters have entirely altered just because it’s autumn and we have less milk.

1. The milk is colder.  Any time it is left standing before the starter goes in, used to be a brief period of pre-ripening time as it was at 27C but very little is happening at 18C.  The lactic acid bacteria activity from the milk itself and from the starter once added is less even if the milk is heated and the starter added at around 31C because where there was a pre-ripening period, now there isn’t.  This in turn affects the quality of the set because the beginnings of acidification would free up a certain amount of calcium ions from the milk which helps for a good set and increases the yield.

2. The milk needs to be warmed up much more slowly and consistently.  To heat quickly, using the ‘flag’ or mini radiator type thing we use to warm milk (it works by running hot water through it) and stir the hot milk in, means it loses temperature more quickly.

3.  Even warmed more slowly, the milk doesn’t keep its temperature in the same way because there’s much less of it.  Whereas with quantities like 70 or 80 litres, the milk might drop 1 degree between adding starter and then adding rennet an hour later, it can now drop 2 or 3 degrees.  Losing temperature more easily again of course means the set will be weaker.

4.  The top of the curd, where you usually test the set, is colder than the lower part of the vat as it’s the area that’s open to the air the most.  Often this will set more weakly than lower down the vat.

Even by increasing rennet and trying to keep the vat next to the dairy’s heaters at all times after it’s been heated, the set just isn’t as strong as it has been.  The implications of this on the cheese are pretty huge.

1.  Weak curd forms a more sloppy substance going into the cloths.  Small and more mushy particles of curd clog up the cloths and reduce the effectiveness with which they let the cheeses drain.

2. Weaker and colder curd drains more slowly anyway.  It doesn’t free drain in the same way.  More cloth pulling only has a limited effectiveness as the cloths are clogged up already and also because with a weaker structure you end up losing fats and squashing the nutrients out of the curd by using more force but still finding that it feels soft and wet in texture.

And the effects of the weaker curd on the drainage cloths are:

Badly formed rinds because they are largely formed from the soft particles that collected on the cloths.  When salting or maturing further, these rinds are loose, too moist and come away from the cheese.

Cheeses that hold free moisture.
That old enemy we’ve been fighting with our draining cloths!  Because the cloths are clogged up, hindering drainage but also because the curd didn’t have enough resistance to the cloths to force out the free moisture when they were pulled up tightly and in the end slightly collapsed under the pressure we have floppier and less stable cheeses when they are turned out.  The effect of this is that the cheeses do not mature in a stable manner.  They don’t retain the calcium which will allow a full and elastic breakdown and they develop what is more of a lactic cheese texture with a very runny breakdown just under the rinds and a curdy, moist, acidic centre.  It’s not that this is unpleasant to eat, in fact it can be very tasty, it’s just not what we want.

Before I began making cheese, I might have tried to explain this to a customer by saying that at the end of lactation with the milk composition being different and the pasture being different, the cheese would change.  Having made cheese for a few months, I would now tell it very differently.  The biggest change has been the temperature.  So much for terroir!

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