Process and Quality Control Procedures
1. General Analytical Requirements
Chemical and microbiological analyses of cheese milk, finished cheese, and cheese whey are required to maintain efficient operations and to ensure food safety and quality. This Section, Part II describes some analytical procedures relevant to cheese making operations, but it is not intended to be a comprehensive process and quality control manual. The following overview of methods is intended to orient the reader to the general types of analyses required in cheese operations.
Milk composition analyses should include both fat and protein, determined by infrared milk analyzers. Note that casein content rather than total protein content is the critical parameter with respect to cheese yield. Many milk analysers are able to measure crude protein, true protein, and casein. See Part III for details on standardization of milk composition and the importance of casein and true protein to cheese yield.
Quality measurements of cheese milk should include total counts (and / or psychrotrophic counts), tests for inhibitors and somatic cell counts. Depending on the types of controls in place at the producer level, cheese makers may need to monitor bacteria counts, inhibitors and somatic cell counts of individual producer milks.
Cheese composition analyses should include fat (by Babcock, Mojonnier, or infrared instruments), moisture, salt, pH and, if possible, protein. Cheese pH should be measured at critical stages during cheese manufacture, 7 days after manufacture, and periodically during curing. Other composition parameters should be determined several days after manufacture to permit time for equilibration of soluble components. Salt, in particular, requires time to become evenly distributed throughout the cheese; in brine or surface ripened cheese, uniform salt distribution may never be achieved. For Cheddar cheese and other vat salted cheese, representative samples for accurate determination of salt content can usually be obtained as early as seven days after manufacture.
With respect to process and quality control, the ‘pH profile’ during manufacture and curing is vital. “pH profile” is a term we use to describe the set of pH values at critical process control points in the cheese making process. Other important process control parameters are the ratio of salt to moisture (SM), the moisture in the non-fat substance (MNFS), and the fat in the dry matter (FDM). These ratios are normally reported as percentages and calculated as follows.
Note: that percent total solids is 100 minus percent cheese moisture
2. Analytical Quality Control
Effective control of quality and plant efficiency requires effective quality control of analytical procedures. Smaller cheese manufacturers generally find it is more economical and reliable to have most analyses performed by an outside laboratory. Some testing however, can be done in house, even for the smallest cheesemakers; pH, TA, brine concentration are all test accessible for even the smallest cheese makers. But, whether the analyses are performed in house or by an outside laboratory, they must be accurate and reliable. In Canada, dairy laboratory accreditation is available via Canadian Laboratory Services (CLS), 1147 Merivale Road, Ottawa, K1Z 6B4, (613) 247-1395. CLS is able to provide ongoing certification for both milk analysis (composition and quality) and cheese composition analysis. I strongly recommend that cheese makers use CLS or other certified testing, whether lab services are provided from inside or outside the company.
Some analytical procedures are detailed in subsequent sections. The reader is also referred to:
- Standard Methods for the examination of dairy products. American Public Health Association, 1015 Eighteenth St. NW, Washington, D.C.
- Official Methods of Analysis of the Association of Official Agricultural Chemists, P.O. Box 540, Benjamin Franklin Station, Washington, D.C.
3. Sampling for Chemical Analysis
Depending on the size and shape, firm to hard cheese should be sampled using a cheese trier (at least 100 g sample) or by taking a sector sample. Soft cheese can be blended for sampling or sector sampled depending on its texture. Sector sampling means taking a sample of uniform thickness across the entire cheese or from the centre to the exterior of the cheese. Cheese samples are stored in opaque airtight containers and fragmented using a grater or another device before analysis. It is important to grind and mix the sample well before sub-sampling for analysis.
If the analytical procedure requires less than a 1 g sample, it is desirable to prepare a liquid cheese homogenate and take a sub-sample from the homogenate. A homogenate suitable for most purposes can be prepared as follows:
- Weigh 40 g cheese into a blender container.
- Add about 100 g of 7% sodium citrate solution.
- Blend until homogenous using a high-speed blender.
- Rinse blender shaft into container and make up to final weight of about 200 g.
Note that cheese is notorious for inhomogeneous composition. Brine salted cheese have pronounced salt and moisture gradients, namely, higher salt and lower moisture near the surface. Large blocks or wheels of pressed cheese will have moisture and pH gradients, namely, increasing moisture and decreasing pH towards the interior. In addition to moisture and salt gradients, surface ripened cheese also has pH gradients because pH increases at the surface during curing. These inconsistencies make it difficult to obtain accurate composition and mass balance (yield) data. A useful approach to improve yield and composition control of large blocks is to set aside small blocks (e.g., 20 Kg blocks of Cheddar) for early composition and quality testing, and subsequently conduct representative sampling of the large blocks (e.g., 240 Kg blocks of Cheddar) during the cut/wrap process.
4. Sampling for Microbial Analysis
Obtain samples as described above for chemical analysis. Triers or knives used for sampling must be flame or alcohol sterilized. Samples should be stored in sterile bags such as Whirl Pack bags at 2-4°C and analyzed within 24 hours.
refers to micro-organisms that are able to grow at temperatures less than 7°C