What type of fermentation occurs when yeast produces alcohol and carbon dioxide?

Primary fermentation is the correct answer because it refers to the initial stage of fermentation in the brewing process, where yeast converts sugars from the wort into alcohol and carbon dioxide. This process typically occurs during the first two weeks of fermentation and is essential for producing alcoholic beverages, particularly beer.

During primary fermentation, the yeast, often Saccharomyces cerevisiae, becomes active and begins consuming the fermentable sugars present in the wort. As the yeast metabolizes these sugars, it produces ethanol, which is the alcohol in beer, and carbon dioxide, which contributes to the beer's carbonation and head. This stage is crucial for establishing the flavor profile and alcohol content of the finished beer.

In contrast, malolactic fermentation is a secondary process primarily associated with wine production, where malic acid is converted to lactic acid. Secondary fermentation in beer can refer to additional fermentation processes that may occur after primary fermentation, often for conditioning or clarifying the beer rather than for the initial production of alcohol and CO2. Spontaneous fermentation refers to fermentation that occurs through naturally occurring yeast and bacteria in the environment, without the addition of cultured yeast, which is not the focus when discussing the primary fermentation process.