Quality control in cheese manufacturing.

QUALITY CONTROL IN CHEESE MANUFACTURING:

In production the main rules are: minimizing expense, while attaining optimum quality. The first requirement can sometimes be in conflict with the latter.

To fulfill the two requirements, the cheese manufacturing process must be adjusted constantly.

Cheese quality can be controlled by observation of the product at the time of sale, but since cheese may not be ready to consume for weeks or months after its manufacture, there will be a great delay in adjustment of the production process. In the meantime, milk characteristics may change so that the proposed adjustment will not be suitable for achieving desired cheese quality.

It is therefore desirable to find a method to control the cheese quality at an earlier moment; preferably right after manufacture, or even better, during the make.

We must design programs for the final cheese quality by controlling manufacturing variables such as :

1. Min. - pH and pH after 6 hours

2. % Moisture

3. Bacteria flora

If we make our adjustment of manufacturing process in relation to such measurements, it is however necessary that we know, which min.-pH, which moisture content and which bacteria flora can lead to optimum cheese quality.

10.1 QUALITY CONTROL WITH THE CHEESE PROCESS IN THE CHEESE VAT:

10.1.1. Acidification:

Titrating of whey at exact times under stirring can show, if the acidification is run normally. In manufacturing of Cheddar and Colby cheese the acidification is followed under "the Cheddar process". The cheese curds stay in the vat after stirring and whey drawing. The final salting and molding happens, when the acid reaches a predetermined level.

10.1.2 % Moisture:

Over the years, many attempts have been made to develop quick methods to determine moisture content, but practical methods are still lacking. Until now, experiments have measured curd density by putting them in salt solutions measuring electric conduction or measuring the electrical constant. The last principle is used for moisture determination in continuous butter making.

10.2 CONTROL WITH THE CHEESE MIN.-pH:

One of the most important tasks in cheese making is to regulate the acidification process in the cheese mass, so the acidity (min. pH) is neither above nor below a definite limit. This limit is very carefully determined for each single cheese type, one must determine which min.pH, gives the best quality.

Consider the following:
Normal cheese with eyes, Emmentaler: pH approx.. 5.20 - 5.25

Maribo, pH approx.. 5.15 - 5.20

Cheddar pH approx.. 5.0

Dana blue (blue pH approx.. 4.7

Camembert pH approx.. 4.5

For most cheeses, the lowest min. pH occurs after 20-24 hours. A pH determination in the cheese at that time gives a good indication of the final cheese quality.

10.2.1.1. The Importance of The Right Min.-pH:

The cheese consistency, moisture binding and ripening depends on min.-pH. A lower min.-pH means, that the cheese becomes less and less elastic and more and more brittle. The cheese moisture binding ability becomes less and less, the lower min.-pH we have in the cheese. The cheese will sweat with temperature swings and the rind is destroyed and becomes unclean.

The ripening will be fairly dependent of min.-pH. The resulting acid formed will depend on, how many bacteria cells are formed. These determine the amount of protein splitting enzymes.

10.2.2. Control With pH Value After 6 Hours:

As has been already stated, the pH in the 24 hour old cheese is an important criteria for the final cheese properties. For establishing the acid development, the exact time the pH is measured should be the same for every vat.

Acidification influences the content of lactic acid, which also influences the content of dissolved/undissolved calcium and phosphoric acid.

If acidification is early in relation to whey drainage, this will mainly mean a change in inoculation time and amount. This will also result in changes in the content of calcium and phosphate.

If acidification occurs later the total content of calcium and phosphate will be influenced to a lesser degree.

An early acid development also influences eye formation in a cheese. Increase in acid will influence C02 production; large C02 production may cause too many holes, small holes and/or no hole development.

It is therefore important to monitor acid development always at the same time for each vat.

10.3 CONTROL WITH CHEESE MOISTURE:

10.3.1 The Cheese Moisture Content and Its Importance

For The Quality:

Moisture content influences the shape, yield and meeting regulatory standards. Moisture content influences shelf life and ripening. A higher moisture content permits faster growth of micro-organisms. Also cheese with a higher moisture content ripens faster, and has a reduced shelf life than lower moisture cheese.

10.3.2 Moisture Content Influence on Consistency:

When discussing cheese consistency, one should differentiate between the two physical material properties: 1) hardness (firmness), 2) elasticity. Moisture content especially influences hardness. Cheese firmness depends on the proportion between liquid and solid matter in the cheese. In the cheese there are two phases, which must be looked at separately: 1) fat phase and 2) the fat-free phase. The cheese firmness will depend on the relation between solid and liquid in these two phases.

1) In the fat phase relation depends on:

a) fat composition (iodine number).

b) the cheese temperature.

2) In the fat free phase the proportion of solid/liquid depends on relation between moisture (liquid) and fat free solid (protein, sugar, milk ash and NaC12 (common salt)). This last consideration may not be quite correct, as sugar and salt are easily dissolve able in water. But protein is found mainly in solid form in the cheese, and as the protein makes up for the main part of the fat-free solids, the relation between moisture and fat-free solids will be important in determining the firmness of the fat free part of the cheese.

Therefore, there is a considerable better connection between the cheese moisture percentage in the fat free part (mffc) and cheese firmness, then there is between cheese moisture and its firmness.

10.3.3 Optimum Moisture Percentage:

For every cheese type there will be certain limits for mffc.

Consider the following:
Samsoe, Elbo, 54 - 56% mffc

Havarti, 57 - 59% mffc

Esrom. 61% mffc

Dana blue (blue cheese) 63% mffc

Rind less 54% mffc

The optimum mffc is a little higher in the winter, (iodine percentage of fat in milk) when iodine is lower. When evaluating percent mffc in the fresh cheese, we must remember, that the percentage should be 2-5% higher, as the moisture percentage falls with salting and storing. For the rind less cheese the lowering of moisture content amounts to normally 2-5%, depending on storing conditions. In regards to moisture distribution in the cheese, we must remember that at the 2-3 week stage the moisture distribution is uniform so that we can determine % mffc with high accuracy.