Which single form of fermentation does not produce gas?

1. All forms of fermentation except lactic acid fermentation produce gas. 2. Lactic acid fermentation is therefore the single gas-free exception. 3. Its equation turns pyruvic acid and NADH into lactic acid and the oxidized carrier, with nothing given off. 4. Alcohol fermentation clearly does release gas, since carbon dioxide leaves when the carboxyl group is removed. 5. The gas produced is used as an indicator of the fermentation of specific carbohydrates. 6. That indicator plays a role in the laboratory identification of bacteria, which only works because most types do give off gas. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 7 "Cellular Respiration", section 7.5 Metabolism without Oxygen_