Question

The desired minimum sugar ratio to be maintained in preparation of sweetened condensed milk is:

• A. 8.5
• B. 42.5
• C. 62.5
• D. 68.5

Hint:

To prevent microbial spoilage in sweetened condensed milk without autoclaving, the sugar index must be kept between 62.5% and 64.5%. This level of sugar concentration effectively binds free water, lowering the water activity (\(a_w\)) below 0.86.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Sweetened condensed milk is preserved primarily by its high osmotic pressure, which is achieved by adding sucrose.
The preservation effectiveness is measured by the "sugar ratio" or "sugar index," which represents the concentration of sucrose in the aqueous phase of the condensed milk.
Key Formula or Approach:
The sugar ratio is calculated using the following formula:
\[ \text{Sugar Ratio (\%)} = \frac{\% \text{ Sucrose}}{\% \text{ Sucrose} + \% \text{ Moisture}} \times 100 \]

Step 2: Detailed Explanation:
Let us analyze the requirements for the sugar ratio in sweetened condensed milk:
- To inhibit the growth of osmophilic and spoilage microorganisms (including bacteria, yeasts, and molds) without heat sterilization, the osmotic pressure must be kept high.
- If the sugar ratio is too low (\(<\) 60.0%), the osmotic pressure will be insufficient, allowing microaerophilic spore-formers or yeasts to grow and spoil the product.
- If the sugar ratio is too high (\(>\) 64.5%), the sucrose may crystallize out of solution, causing a gritty, sand-like texture defect.
- Therefore, the industry standard is to maintain the sugar ratio within the range of 62.5% to 64.5%.
- A minimum sugar ratio of 62.5% is specified to ensure preservation while keeping the sucrose fully dissolved.

Step 3: Final Answer:
The desired minimum sugar ratio to be maintained is 62.5. Hence, the correct option is (C).