Standardizing of milk for Cheesemaking.

Protein-Fat ratio.

The relative amounts of protein and fat in milk are described as the protein-fat ratio or P/F where

P/F =protein / % fat

Fat content of cheese is often reported as a ratio of percent fat in the cheese to the total solids or dry matter of the cheese. This ratio is called fat in dry matter of F/DM where

F/DM = % fat / % dry matter

The percent fat in cheese is determined by two factors: the percent moisture in the cheese and the P/F of the milk. However F/DM depends mainly on the P/F of the milk. Therefore, the value of F/DM is used to calculate the amounts of protein and fat, which are required in the milk to give the desired fat content of the cheese.

The protein content can be determined from the following formula:

% protein = (0.45179 x % fat) + 1.5214

Methods of Standardizing:

1. Addition of skim milk powder (or condensed skim.)
2. Addition of skim milk.
3. Removal of cream.

These methods are based on the assumption that the milk has high fat content relative to the protein content. It is well known that as the fat content of milk increases, the protein also increases, but at a slower rate.

Calculations:

The following steps are required to calculate the amount of powder or skim milk to be added, or the amount of cream to be removed. Suppose a cheese maker has 10,000 kg of milk which he/she wishes to make into Swiss cheese.

Step 1. Determine the protein and fat content of the milk using an automatic milk analyzer (LactiCheck in 85 sec.)

Step 2. Determine the required fat, moisture and F/DM of Swiss cheese. ?Dairy Products Regulations? of the Canada Agricultural Products Standard Act require Swiss cheese to contain a minimum of 27 % fat and a maximum of 40 % moisture.
Therefore
F/DM = % fat / % dry matter = 27 / (100 ? 40)= 45 %

Step 3. Determine the required P/F of the milk. At the present time it is not possible to accurately predict the required P/F for all types. When the desired F/DM is 50 % as it is for Cheddar cheese, the required P/F = 0.96. For this special case) where F/DM = 50 % and P/F = 0.96), the required amounts of fat to be removed or powder to be added can be read from a table. The P/F required to yield F/DM = 45 % is about 1.15
(regarding p/f ratio, cheese makers work mostly within historical data for a given process.)

Step 4. Calculate the amount of: (A) skim milk powder to be added or; (B) fat to be removed or; (C) skim milk to be added.

A. Adding skim milk powder.

(i) Calculate the protein required to give P/F = 1.15
P/F in the milk = % protein / % fat = 3.1 / 3.5 = 0.89
The required level of protein = 1.15 x % fat
= 1.15 x 3.5 = 4.03
(ii) The protein to be added = 4.03 ? 3.1 = 0.93 %
(iii) Calculate the weight of protein which must be added to 10,000 kg of milk.
The required weight of protein = 0.93 % of 10,000
= (0.93 / 100) x 10,000 = 93 kg
(iv) Calculate the amount of powder, which must be added.

Skim milk powder contains 35 % protein.
Required amount of powder = 100 / 35 x 93 = 266 kg.

(B) Removing fat.

(i) Calculate the % fat required to give P/F = 1.15
P/F in the milk = % protein / % fat = 3.1 / 3.5 = 0.89
The required level of fat = % protein / 1.15 = 3.1 / 1,15 = 2.70
(ii) % fat to be removed = 3.5 ? 2.70 = 0.80
(iii) Calculate how much fat must be removed from 10,000 kg milk
Amount of fat to be removed = 10,000 kg x 0.80 /100 = 80 kg.
(iv) Calculate how much cream must be removed assuming the cream
contains 30 % fat.

Weight of cream = 80 kg x 100 / 30 = 267 kg.