3. Overview of bioethanol production processes

Bioethanol is essentially produced by fermentation of sugars and starch-rich materials. A distinction is usually made between several generations of bioethanol, depending on the source of the raw material (see box):

• first-generation bioethanol produced by hydrolysis and then fermentation of plants rich in cellulose, starch or hemicellulose;

• second-generation bioethanol produced by hydrolysis and fermentation of lignocellulose-rich plants;

• third-generation bioethanol produced enzymatically on microalgae or yeast.

The latter technology essentially produces oils (which can be upgraded to biodiesel), but research is underway to steer this third-generation biofuel towards ethanol production. What's more, growing microalgae requires large quantities...