Runny blue - slipskin?

[Jackbcheesy]

Hi everyone!

Gooey blue cheese question for the experts! My first attempt at a blue was going well for the first three weeks (photos below). After about 4 weeks it started to get a bit squishy under the rind (but firm in the core) and got a few tears when turning which oozed a very runny liquid cheese. After that I put the cheese in a container in the fridge to try and slow down maturation. The lower temp also firmed up the cheese. It's about 10 weeks now and the rind and 'mantle' (sorry for the geology jargon) of the cheese are firmer but the core is now runny, even at 4•c (photo below). Tastes quite nice, sharp, but would turn to mush at any temperature above 10•c.

Any ideas where I went wrong? Was there too much moisture in the curds maybe, or drying and maturation occurring at a high temperature? Or did I age too long? Thanks in advance!

[mikekchar]

Well a combination of too much moisture and too much acidity (which may go hand in hand).  Cheese goes runny because the mold produces ammonia.  The ammonia soaks into the cheese and raises the pH.  The higher the pH goes, the more runny the cheese gets.  So why does a low pH (more acidity at the beginning) cause a problem?

Milk contains a salt called calcium phosphate.  This is where virtually all of the calcium in milk comes from.  Almost all of the calcium phosphate exists wrapped up in casein protein bundles called "micelles".  Those same protein bundles are what we make cheese from.  Incidentally, this is why the cheese is white and the whey is clear -- all of the calcium phosphate ends up in the cheese because it's wrapped up in the protein.  It's the calcium phosphate that makes milk white.

Anyway, when you put the casein micelles (milk protein bundles) in an acidic environment, some of the acid reacts with the calcium phosphate.  It's actually the calcium phosphate that glues together the protein strands into the bundle (in ways that nobody understands, even now).  This allows the micelles to relax a bit and to stretch.  This is, in turn, is why reducing the pH of the curd to 5.1 to 5.3 allows the cheese to stretch and melt.  (So much trivia, so little time...)

Now the interesting part here is that the calcium phosphate acts just like baking powder when you add acid -- it neutralises the acid.  As you add more acid, the pH just stays in one place and doesn't move until the acid reacts with all the calcium phosphate.  This is called "buffering".  Remember that the calcium phosphate is bound up in the protein bundles (casein micelles).  It's not all available all at once.  It takes time to leak out.  So the milk gradually acidifies over time.  But the pH can bounce around a bit and even go back up over time if you are producing acid slowly enough (this is actually a problem in the mozzarella industry where they get a pH "rebound" after it has been stretched and the resultant cheese will no longer stretch -- so they aim for a lower than optimal pH when initially making the cheese).

More trivia: The amount of calcium phosphate in the milk and the speed at which it can get dissolved out of the casein micelles is completely dependent upon the milk.  So if you take milk from 2 different cows and add the same amount of acid to it, they will end up with different pH at the end, even though they started at the same pH.  That's because the different milks have different "buffering capacity".  That's why "quick mozzarella" is a complete crap shoot.  Will you have the correct amount of acid to counter the calcium phosphate in your milk?  Only if you are lucky and there is basically no way to tell how much acid you need ahead of time.  (I'm really going off topic).

So anyway....  If you let your cheese get as acidic as it can get, it will dissolve most of the calcium phosphate.  That calcium phosphate will react with the acid and be gone.  Then when you add ammonia to the cheese, there is nothing to buffer the pH change!  It will rise quickly. 

There is another important thing you need to know.  Proteins are large chemical structures (hundreds of times bigger than a normal molecule).  Overall, casein micelles have a positive or negative charge (they are positive before rennet works on it and negative after rennet works on it -- I won't get into the details here).  However, as the solution that the protein is in gets more and more acidic, the protein bundle loses it's average negative charge (it gets weaker and weaker).  At some point, it has an average charge of zero.

One thing you probably have never thought about, but is important here, is what it means to be "dissolved".  Why the heck can you put something in water and it basically disappears???  As it turns out, water (H2O) is kind of a cool molecule.  It's shaped like a boomerang with O in the middle and an H on either side.  The H has a negative charge and the O has a positive charge.  Because of it's shape, basically one side of it has the Hs and one side the O.  It's powerful enough that it will split up other chemicals (mostly salts) and force the negative particles to hang out with the O side (opposites attract like a magnet) and the positive particles to hang out with the H side.  This is what "dissolved" means.  When you take the water away, the particles find their long lost lovers and reunite.

Well, casein basically does the same thing.  When it's charged, it hangs out on one or the other side of the water molecule.  This is called being "hydrophillic"  It's not really "dissolved" (it doesn't split apart), but basically each bundle is forced to be evenly distributed through the water and so it just becomes part of the liquid.  When the bundle loses its charge (due to the acidity), it no longer needs to hang out distributed through the water.  It becomes "hydrophobic" and clumps up (mostly sticking together thanks to the globs of fat, or just friction).  This is what happens when you coagulate milk using an acid (Rennet is different, but I won't talk about that now).

The super duper cool thing is that if you take acidic curds and *raise* the pH, the opposite thing happens!  The bundles of proteins get charged up again and are forced to hang out distributed through the water.  The higher the pH, the more it will happen and the more runny your cheese will get.

If you made it this far, you deserve to eat lots of cheese for your efforts :-)  But I can now answer your question.  If you salt your cheese at a higher pH, it will stop the starter culture earlier.  This will stop the acid production.  This will keep your cheese at a relatively high pH.  This will *preserve* the calcium phosphate in the casein bundles, which means that it will be available to stop the ammonia from raising the pH too high.  This will stop your cheese from getting too runny.  This is the secret to "stabilised paste" camembert :-)  No matter how long you age it, it will not get runny.

Now, of course, if you have less moisture in the cheese it will also be less runny because there is less water to for the protein to be spread out it. (That last sentence was depressingly easy to describe -- surely there is something more complicated about it :-D )

Hope that helps!

[John@PC]

If you salt your cheese at a higher pH, it will stop the starter culture earlier.  This will stop the acid production.  This will keep your cheese at a relatively high pH.  This will *preserve* the calcium phosphate in the casein bundles, which means that it will be available to stop the ammonia from raising the pH too high.  This will stop your cheese from getting too runny.

So a lower pH at salting makes for a higher (and softer / runnier) cheese during aging?  Is there an impact on flavor either way?  Caldwell sets a target curd pH of 4.7-4.8 before salting for a rindless blue; is this a good range?  Thanks.

[mikekchar]

Yes, it's ironic that the lower the pH you get to in the make, the faster you can get to a higher pH on the aging side (i.e. it takes less ammonia to pull the pH back up).  And, yes, it affects the flavour quite a lot.  Your pH target for a blue depends a lot on what kind of blue you are making and how long you are going to age it for.  Also, it depends a lot on the rind treatment.  For example, it's common for both Stilton and Gorgonzola to get brevibacterium linens going on the rind and then *really* dry it out (much like an alpine rind).  This reduces the amount of ammonia you are producing and lets you age the cheese for a long time.  But other cheeses let it go blue all the way out to the rind and you really have to eat it young or it will basically melt on you.  I think the easiest way to think about it is that a Brie is made with penicillium candidum while a Roquefort is made with penicillium roqueforti -- they are both penicillium molds.  They soften the paste similarly.  Caldwell *does* suggest a pH of 4.8 for the rindless blue recipe and 4.7 for the natural rind recipe.  However, the rindless is wrapped tightly to keep out oxygen (and hopefully stop the blue from growing) and the natural rind is only aged for 60-75 days (like a Bie).  It's super important to have a large cheese that is about the same height at width so that you minimize the surface area to volume ratio.  This means that the surface mold (which has the most oxygen and grows the fastest) produces less ammonia per volume of the cheese (because there is less of it) and thus will soften more slowly.  If I were doing it, I would also age it in the normal fridge after the blue takes hold just to slow it down even more.  This allows the ammonia to transport into the paste so that it doesn't get too soft on the edge.  I do this with all my rind ripened cheeses (washed rinds and bloomy rinds as well).