Defects and grading
Common Cheese Defects
Body: in the context of modern sensory analysis body refers to texture, which is confusing because cheese graders use the term “texture” to refer to cheese openness. Here, we will use the traditional cheese grading terms. Some descriptors for body defects are:
Crumbly/short: often due to excess salt or acid.
Corky: due to overcooking, low fat, low moisture, or excess salt.
Mealy: this defect can be detected on the palate or by massaging the cheese between the thumb and forefinger. It is usually associated with excess acidity.
Pasty: sticks to the palate and fingers; due to excess moisture.
Weak: breaks down too quickly when worked by hand due to excess fat or moisture.
Texture: relates to openness in the cheese which may or may not be desirable depending on the type of cheese and the cause of openness. Openness can be due to:
Mechanical openings, which are holes of irregular shape caused by trapped whey. Trapped whey makes the impression in the cheese during pressing, but during ripening the moisture is dispersed throughout the cheese leaving the hole behind. Mechanical openings can lead to discolouration around the opening due to local acid development. Undesired mechanical openings can be reduced or closed by vacuum packaging.
Gas holes, which are desirable in many types of cheese. Gas hole defects include:
- Early gas defects due to coliforms. These appear as small, spherical, shiny holes. The defect is often associated with unclean flavour.
- Late gas due to Clostridium tyrobutryricum or perfringens, especially in some European made cheese. Clostridia spores are often present in American cheese as well but do not normally cause problems. However, they may be activated by heat treatment and, therefore, sometimes cause gas defect in processed cheese.
- A third gas defect occurs in Cheddar and American types. The defect is distinctive in that the gas (mainly CO2 with some hydrogen sulphide) blows the package but not the cheese. The defect occurs at 6 - 9 months in Cheddar, but a similar defect is sometimes observed earlier in American Mozzarella and Colby. The causative anaerobic organism is not fully identified; however, experiments have demonstrated that the defect does not occur in cheese aged at < 10°C.
- Yeast slits due to yeast growth.
Flavour: most grading systems assign the greatest weight to flavour defects. A few common descriptors are:
Acid flavour is often associated with acid body defects noted above. The common causes all relate to process control:
- Too much moisture (i.e., too much lactose).
- Too much starter (i.e., too much acid development before draining).
- Salting too late or too little.
- Too warm during or immediately after pressing.
Bitter flavours are common defects in American but also other cheese, including fresh cheese. Some causes include:
- High moisture.
- Excess rennet.
- Bitter cultures.
- High ripening temperatures.
Fruity/Yeasty flavours are usually associated with high pH and bitterness, and sometimes with yeast slits.
Unclean flavours are reminiscent of the barnyard, and may be associated with coliforms.
Whey taint is due to high moisture and is usually associated with acid defects including bitterness.
Colour: other than traditional colour preferences such as orange Cheddar and white goat cheese, the most important colour parameter is uniformity. Even for cheese such as Colby, which is coloured with annatto, graders do not evaluate colour intensity. Rather, they look for non-uniformity, which may signal a manufacturing defect. Some common descriptors are:
Acid cut (pink or bleached): low pH, oxidation of annatto.
Mottled: may be an acid defect or caused by mixing cheese from different vats.
Seamy: this is a Cheddar defect where the curd particles fail to knit properly. Causes Include:
- Greasy curd from too much fat or high temperature during pressing.
- Improper salting, too soon after milling or pH at salting is too high or too low.
- Hooped too soon after salting.
Finish: a lot of art and patience are required to produce cheese with a good finish. Common defects are:
Checked/Cracked: too dry on surface.
Greasy: temperature too high during pressing or curing.
Mineral Deposits due to calcium lactate.
- Common on Cheddar cheese and sometimes on American varieties
- Encouraged by certain non-starter Lactobacilli and Pediococci which favour formation of D-lactate which in turn encourages crystallization of DL-calcium lactate.
- Control measures are:
- Decrease numbers of non-starter bacteria (e.g., pasteurize versus heat treat and/or bactofuge the milk).
- Use tight packaging. Calcium lactate crystals tends to form in areas where the package is loose or in depressions on the cheese surface.
- Avoid temperature fluctuations. Calcium lactate crystals often form in the dairy case where temperatures are not constant.
- Encourage rapid turnover in the dairy case.
Rind rot caused by mites or mold.
Surface mold is definitely one of the most common defects. A frequent consumer question is about the safety of moldy cheese.
Unsymmetrical/Rough: poor workmanship.