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DAIRY FOODS – Cheese – “Souring” the Batch

DAIRY FOODS – Cheese Processing Methods


The process of making cheese requires the separation of milk into solids (curds) and liquid (whey).

This separation is accomplished by acidifying (souring the batch) the milk and adding rennet. 


There are two common ways to “sour” the batch in cheese processing:


      1.   Cheese Separation – The Acid Method :


The acidification process of some fresh cheeses is by the direct addition of an acid like vinegar (acetic acid), lactic acid or phosphoric acid, but the curds produced are very fragile. To alter the curds and prevent fragility, an enzyme is added to promote curdling at lower temperatures.

The addition of rennet (enzyme) is a common method to produce a stronger and more flexible (rubbery) curd with pseudo-plastic physical properties. This allows curdling at a lower /acidic pH (Power of Hydrogen; a scale to measure 7.1 and above for alkalinity vs. 6.9 and below for acidity) which is important because the flavor-making bacteria are inhibited in high-acidity environments.

Many manufacturers use magnesia to “buffer” the pH to lower levels to keep the fermentation process optimized for the microflora activity. It is common for softer, smaller, fresher cheeses to be curdled with higher levels of acid to rennet. Harder, larger, longer-aged varieties like cheddar require lower levels of acid to rennet.

2.   Cheese Separation – The “Starter Culture Medium” Method:


“Starter culture” is live beneficial microflora bacteria with the possible addition of fungi (yeast and molds) that convert milk sugars into lactic acid through the process of fermentation. Sometimes mixtures of microflora colonies and/or enzymes are added to create the “complete culture medium” which is added to the cheese vat (stainless steel vessel) to kick start the fermentation process to produce cheese.

These microbiological cultures are well colonized by microflora to start and accelerate the fermentation process; which also acts to minimize interference from unwanted bacterial strains. These same bacteria and the enzymes they produce promote the development of the final flavor profile displayed in aged cheeses.

Most cheeses are made with starter bacteria from the Lactococci, Lactobacilli, or Streptococci families. Swiss starter cultures also include Propionibacter shermani, which produces carbon dioxide gas bubbles during aging, giving Swiss cheese or Emmental its holes (commonly called “eyes”).