# How many ATP are produced in fermentation?

> Lactic acid and alcoholic fermentation each yield two net ATP per glucose. All of that ATP comes from glycolysis; the fermentation reactions add no more.

Fermentation produces **2 net ATP** per glucose, whether it ends in lactate, as in a sprinter's muscles, or in ethanol and carbon dioxide, as in brewer's yeast. All of that ATP comes from [glycolysis](/guides/how-many-atp-are-produced-in-glycolysis), which makes four ATP and spends two. The fermentation step itself, which turns pyruvate into lactate or ethanol, makes none.

So fermentation does produce ATP, but only because it keeps glycolysis running. Converting pyruvate regenerates the NAD<sup>+</sup> that glycolysis consumes, and without it glycolysis would stall. Aerobic respiration gets about 15 times more ATP from the same glucose.

## How many ATP are produced in fermentation?

Glycolysis first invests two ATP and later produces four, leaving two net ATP per glucose. It also forms two pyruvate and two NADH. The fermentation reactions transfer electrons from NADH to a carbon product, restoring the NAD<sup>+</sup> that glycolysis needs to continue. The two NADH made in glycolysis are oxidized again, so fermentation ends with no net NADH.

![Glycolysis produces four ATP and uses two, leaving two net ATP, while the later fermentation reactions produce no additional ATP](/images/charts/fermentation-atp-accounting.webp '**Figure 1. ATP balance of fermenting one glucose molecule.** ATP used is shown as a positive magnitude so that production, investment and net yield can be compared. The pyruvate-to-product step contributes no ATP. Source: [Alberts et al. (2002)](https://www.ncbi.nlm.nih.gov/books/NBK26882/).')

## Does fermentation produce ATP?

Yes, if fermentation means the whole anaerobic pathway, and no if it means only the final step. Textbooks usually say that fermentation produces two ATP because they count glycolysis and the conversion of pyruvate as one pathway. The reactions that convert pyruvate to lactate or ethanol produce zero ATP; the pathway's two ATP were already made during glycolysis.

## How many ATP are produced in lactic acid fermentation?

Lactic acid fermentation yields two net ATP and two lactate molecules per glucose.

Human cells reduce two pyruvate molecules to two lactate molecules. Lactate dehydrogenase uses the two [NADH from glycolysis](/guides/how-many-nadh-are-produced-in-glycolysis) and returns two NAD<sup>+</sup>. This reaction adds no ATP, but the recycled NAD<sup>+</sup> allows glycolysis to keep producing two net ATP per glucose.

The name “lactic acid fermentation” is common, although lactate is the dominant form at physiological pH. The ATP count is unchanged.

## How many ATP are produced in alcoholic fermentation?

Alcoholic fermentation yields two net ATP, two ethanol molecules, and two carbon dioxide molecules per glucose.

Yeast first converts the two pyruvate from glycolysis into two acetaldehyde and two carbon dioxide. It then reduces acetaldehyde to ethanol, oxidizing two NADH back to two NAD<sup>+</sup>. Neither step produces ATP, so the net yield remains the two ATP made during glycolysis.

Lactic acid and alcoholic fermentation therefore have the same ATP yield but different carbon products. Lactic fermentation retains all six glucose carbons in two lactate molecules. Alcoholic fermentation divides them between two ethanol and two carbon dioxide molecules.

## How does fermentation compare with respiration?

  <caption><strong>Table 1. Fermentation and aerobic respiration compared.</strong> Yields per molecule of glucose. Sources: Alberts et al. (2002), Rabinowitz and Enerbäck (2020).</caption>
  <thead>
    <tr>
      <th scope="col">Pathway</th>
      <th scope="col">Net ATP per glucose</th>
      <th scope="col">Electron acceptor for glycolytic NADH</th>
      <th scope="col">Main end products</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Lactic acid fermentation</td>
      <td>2</td>
      <td>Pyruvate</td>
      <td>2 lactate</td>
    </tr>
    <tr>
      <td>Alcoholic fermentation</td>
      <td>2</td>
      <td>Acetaldehyde</td>
      <td>2 ethanol, 2 CO<sub>2</sub></td>
    </tr>
    <tr>
      <td>Aerobic respiration</td>
      <td>About 30 to 32</td>
      <td>Oxygen, through the electron transport chain</td>
      <td>6 CO<sub>2</sub>, water</td>
    </tr>
  </tbody>

Fermentation stops after glycolysis, so its only ATP comes from substrate-level phosphorylation. Aerobic [cellular respiration](/guides/how-many-atp-are-produced-in-cellular-respiration) sends pyruvate into the [Krebs cycle](/guides/how-many-atp-are-produced-in-the-krebs-cycle) and uses NADH to drive [oxidative phosphorylation](/guides/how-many-atp-are-produced-in-oxidative-phosphorylation), which is why it produces roughly 15 times more ATP per glucose.

Fermentation is also different from anaerobic respiration. Some microbes, such as sulfate-reducing bacteria, still run an electron transport chain without oxygen by passing electrons to an inorganic acceptor like sulfate. Fermentation uses no electron transport chain; an organic molecule made from glucose accepts the electrons instead.

## Does every type of fermentation produce two ATP?

Two ATP per glucose is the standard answer for homolactic fermentation and alcoholic fermentation through glycolysis, but it is not a universal yield for every microbial fermentation.

Microorganisms can use other substrates, routes, and end products. Heterolactic fermentation, for example, yields one ATP when glucose is converted to lactate, ethanol and carbon dioxide, and two when the bacterium makes acetate instead of ethanol.

The two-ATP figure remains the correct count for the classic lactic acid and alcoholic pathways taught in biology courses.