Feta cheese and brine pH

[Bernardsmith]

I started some feta cheese last night (my first) and set aside some of the whey to use as the liquid for the brine. I measured the pH of the whey tonight and it's 6.05. Is there a  target pH I should be looking for ? Thanks.

[Kern]

Feta cheese has a pH of 4.5 to 4.7.  Ideally, your brine is in that range.  You can use the whey if you like but add a little bit of vinegar until the pH gets to the 4.6 +/- pH range.  If your feta gets soft and slimy on the outside you need to add some calcium chloride to the whey brine.  You can avoid this risk by adding a tablespoon per gallon of whey before you add the cheese. 

[Bernardsmith]

Thanks Kern. I checked (and tasted ) the feta tonight and while it was very tasty there was some slime developing. I re-calibrated my pH meter and see that a more accurate reading was 5.05. The fact that I added some Calcium Chloride to the milk before I added the culture does not mean that there will be enough in the whey ?
Is the best way to deal with this sliminess to allow the curds to air dry ?
Thanks 

[Gregore]

If your getting any slime  add more calcium chloride as it will just get more so

[Bernardsmith]

Thanks Gregore. You took the question right out of my mouth. What I did was transfer the feta from the whey-based brine to a water based brine I had used last week when I was making some Caerphilly. The pH of that brine was about 4.07 (and I had added Ca Cl to it). Is the slime bacterial or is it coming from fats and calcium being extracted from the cheese?

[Gregore]

The calcium is coming out of the cheese to balance out the brine becuase the brine is lower in calcium

I am sure a chemist would add a lot more detail but that is my understanding of it.

[Kern]

Calcium binds the proteins into a network that resists dissolution in aqueous solutions.  If the calcium content of the water/whey is too low calcium will be dissolved out of the cheese and the proteins become unbound and slimy.  If this happens remove the cheese, wash the slime off under running water and replace the cheese in a salt solution with the proper pH and the proper amount of calcium.  Caldwell states for feta aging brines to use 0.74 pounds of salt, one teaspoon of vinegar and 1 tablespoons of liquid calcium chloride solution per gallon of water.  I found this to be too low in calcium so doubled the calcium and had no more slime.  The slime is not coming from bacterial decay.

[Gregore]

Thanks kern I knew you would know  why  in chemist speak 

[Bernardsmith]

Calcium binds the proteins into a network that resists dissolution in aqueous solutions.  If the calcium content of the water/whey is too low calcium will be dissolved out of the cheese and the proteins become unbound and slimy.  If this happens remove the cheese, wash the slime off under running water and replace the cheese in a salt solution with the proper pH and the proper amount of calcium.  Caldwell states for feta aging brines to use 0.74 pounds of salt, one teaspoon of vinegar and 1 tablespoons of liquid calcium chloride solution per gallon of water.  I found this to be too low in calcium so doubled the calcium and had no more slime.  The slime is not coming from bacterial decay.

So that is about 9.25% brine solution ?

[Kern]

It is about 8% calculated as follows:  1 gallon on water + 0.74# of NaCl = 8.34 + .74 = 9.08#.  .74/9.08 = .081 or 8.1%