Industrial alcohol substrates: which of the following is NOT a principal feedstock used for large-scale ethanol production by fermentation?

Introduction / Context:
Traditional fermentation industries produce ethanol using carbohydrate-rich, low-cost feedstocks available at scale. Recognizing principal substrates versus marginal or emerging alternatives helps clarify classic process design and historical practice versus modern pilot projects.

Given Data / Assumptions:

• Classic substrates include molasses (cane/beet), starch mashes (from grains), and sulphite waste liquor from pulp mills.
• “Principal” denotes historically dominant, widely deployed feedstocks.
• Wood waste contains lignocellulose and typically requires extensive pretreatment and hydrolysis; it is not a classic principal feedstock in conventional plants.

Concept / Approach:
Evaluate each option’s historical and industrial prevalence. Black strap molasses and sulphite waste liquor are textbook principal feeds. Starch mashes converted to fermentable sugars via amylolytic enzymes are also principal. While glucose is fermentable, purchasing refined glucose as the main feed is rarely economical compared with the above bulk sources. Wood waste, although a focus in modern cellulosic ethanol R&D, was not a principal feedstock for traditional fermentation plants.

Step-by-Step Solution:

Verification / Alternative check:
Surveying industrial references shows molasses, starch hydrolysates, and sulphite waste liquor as core feedstocks; cellulosic routes from wood waste remain specialized or developmental.

Why Other Options Are Wrong:

• Black strap molasses: Classic principal feedstock.
• Sulphite waste liquor: Historically important in regions with pulp industry.
• Glucose: While not cost-optimal, it is a direct, fermentable sugar—more principal than wood waste in legacy plants.
• Starch mash: A principal route after liquefaction and saccharification.

Common Pitfalls:
Confusing modern cellulosic ethanol research prominence with historical industrial prevalence; assuming any fermentable carbohydrate is economical at scale.

Final Answer:
Wood waste