Microbial changes in Camembert

In Camembert and related surface mould-ripened cheeses, the mesophilic starter reaches perhaps 10^9 cfu/g at the end of manufacture. Spores of Penicillium camemberti may be added to the milk or sprayed on the surface of the cheese after moulding. Initially, the surface microflora is composed of adventitious acid-tolerant yeasts and Geotrichum candidum. P. camemberti appears after about 6 days and dominates the ripening of Camemert and Brie-type cheeses. Eventually, towards the end of ripening, a Gram-positive bacterial microflora begins to develop. These organisms, that are often pigmented, are adventitious and similar to those found of the surface of smear-ripened cheeses.

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Fate of the starter in Cheddar

The starter grows during Cheddar cheese manufacture from ~10^7 to 10^8-10^9 cfu/g and reduces the pH from that of milk (~6.7) to ~5.4 at the point of milling. Since Cheddar is a dry-salted variety, and unlike many other cheeses, acidification must be close to complete at the end of manufacture and before salt addition. Salt-in-moisture levels increase rapidly in Cheddar due to the large surface area of the curd chips.

During the early stages of ripening, viable starter counts decrease rapidly at a strain-dependent rate. This decline is due to the unfavourable conditions in cheese for the growth and survival of lactococci: low pH, high concentration of NaCl and lack of fermentable carbohydrate. The salt-in-moisture level largely determines the rate of utilisation of residual lactose in the cheese which is of significance to cheese quality.

After death, the lactococci lyse at a rate that is strain dependent and contribute many important enzymes to cheese ripening (particularly its battery of peptidases but also esterases). There is evidence emerging that starter cells may be metabolically active but non-culturable during ripening and that they may contribute to amino acid catabolism in that state.

NSLAB

Non-starter lactic acid bacteria (NSLAB) are a common component of the microflora of many cheeses and nearly all hard ripened varieties. In a cheese such as Cheddar, they are perhaps the only aspect of the cheese that remains largely uncontrolled.

NSLAB in Cheddar are usually wild strains of Lactobacillus paracasei/Lb. casei that probably gain access to the cheese from the raw milk by surviving pasteurization or from the cheesemaking environment. These organisms grow from very low numbers and typically reach about 10^7-10^8 cfu/g within 2-3 months. They have enzyme systems generally similar to those of Lactococcus and probably contribute to ripening or indeed to the development of off-flavours (research in New Zealand has suggested many flavour defects in Cheddar made under best practice are due to NSLAB). NSLAB are the dominant viable microflora of mature Cheddar cheese. Ripening temperature and, significantly, the rate of cooling of Cheddar blocks after manufacture are major factors which control the growth rate of NSLAB.

Techniques in the literature used to study the contribution of NSLAB to ripening include comparison of raw and pasteurised milk cheeses, microfiltration, use of antibiotics, aseptic cheesemaking and low ripening temperatures.

Further information:

Fox, P.F., P.L.H. McSweeney and C.M. Lynch (1998). Significance of non-starter lactic acid bacteria in Cheddar cheese. Australian Journal of Dairy Technology 53, 83-89.