Alcohol industry by-products – identity of fusel oil Fusel oil obtained in spirit production is best described as:

Introduction / Context:
During fermentation and distillation of spirits, by-products accompany ethanol. ‘‘Fusel oil’’ is a well-known fraction that has implications for beverage quality, industrial alcohol purification, and effluent handling.

Given Data / Assumptions:

• Feedstock: molasses or other sugar substrates.
• Process: yeast fermentation followed by distillation.
• Focus: identity and composition of fusel oil.

Concept / Approach:
Fusel oil is the higher-boiling side stream comprised mainly of higher alcohols (e.g., amyl alcohols, propanol, butanol), small amounts of aldehydes, and esters. It is separated from spirit streams and can be processed or disposed of depending on application. It is not an essential oil nor an herbal extract; it arises from fermentation by-products and distillation cut management.

Step-by-Step Solution:

Verification / Alternative check:
Distillation practice and beverage technology references list isoamyl alcohol as a principal component of fusel oil; industrial alcohol plants recover or treat this by-product.

Why Other Options Are Wrong:

• Essential oil / herbal extract: Derived from plants via steam distillation/solvent extraction, not from molasses fermentation.
• None of these: Incorrect since the precise definition is provided in option (c).

Common Pitfalls:
Assuming all distilled oily fractions are essential oils; in fermentation distillation, ‘‘oily’’ refers to higher-alcohol mixtures rather than terpene-rich essential oils.

Final Answer:
mixture of higher molecular weight alcohols (a by-product obtained during production of alcohol from molasses).