Question

To obtain smooth texture in sweetened condensed milk, the desired lactose crystal size is

• A. <20\(\mu\)m
• B. <30\(\mu\)m
• C. <15\(\mu\)m
• D. <10\(\mu\)m

Hint:

SCM Lactose Crystal Sizes:
Desired Smooth Texture = $\mathbf{< 10\;\mu\text{m}}$ (Undetectable on palate).
Sandy Gritty Defect = $> 15 - 20\;\mu\text{m}$.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Controlled lactose crystallization seeding in sweetened condensed milk: flash cooling and seeding with finely ground $lpha$-lactose monohydrate ($30^\circ ext{C}$) induces millions of micro-crystals $< 10\ \mu ext{m}$, below human tongue organoleptic detection threshold to ensure smooth velvety texture.
Key Formula or Approach:
\[ \text{Lactose Crystal Size in SCM: } \mathbf{ 15 - 20\;\mu\text{m (Sandy / Gritty Defect)} \]

Step 2: Detailed Explanation:
In the manufacturing technology and texture control of Sweetened Condensed Milk:
- SCM is supersaturated with lactose; without controlled cooling, lactose spontaneously grows into large, sharp, jagged tomahawk crystals ($> 20\;\mu\text{m}$) causing severe 'Sandiness' defect.
- During manufacture, condensed milk is cooled to the optimum seeding temperature ($30^\circ - 32^\circ ext{C}$) and seeded with finely pulverized $\alpha$-lactose monohydrate seed powder ($0.05\% - 0.1\%$, seed size $< 5\;\mu\text{m}$) under intense agitation for 60 minutes.
- This forces lactose to crystallize rapidly into billions of microscopic crystals where the desired lactose crystal size is strictly less than 10 micrometers (< 10 \(\mu\)m) (average $6 - 8\;\mu\text{m}$) (D).
- Crystals $< 10\;\mu\text{m}$ cannot be resolved by tactile sensory papillae on the human tongue, producing a luxurious, smooth, velvety texture.

Step 3: Final Answer:
Thus, the desired lactose crystal size is <10\(\mu\)m, matching option (D).