Fermentation (lactic and alcoholic)
Fermentation is an anaerobic pathway that allows cells to keep producing ATP through glycolysis when oxygen is limited.
The key idea is NAD+ regeneration: fermentation re-oxidizes NADH back to NAD+, so glycolysis can continue.
In the simplified accounting used here, the only ATP counted is the net ATP from glycolysis: 2 ATP per 1 glucose.
Two common types
1) Lactic fermentation (many bacteria; animal muscle cells under low oxygen)
The pyruvate made in glycolysis is reduced to lactate. This consumes NADH and regenerates NAD+.
2) Alcoholic fermentation (yeast; some plant tissues)
Pyruvate is converted to ethanol and CO2. NADH is used in the final reduction step to regenerate NAD+.
Model reactions used in this calculator
These are standard educational stoichiometric forms (used to compute product yields and a carbon check).
Lactic fermentation
\[
\begin{aligned}
\mathrm{C_6H_{12}O_6} &\rightarrow 2\,\mathrm{C_3H_6O_3} + \text{net } 2\,\mathrm{ATP}
\end{aligned}
\]
Alcoholic fermentation
\[
\begin{aligned}
\mathrm{C_6H_{12}O_6} &\rightarrow 2\,\mathrm{C_2H_6O} + 2\,\mathrm{CO_2} + \text{net } 2\,\mathrm{ATP}
\end{aligned}
\]
Stoichiometric yield rules
Let nglc be the amount of glucose (in moles).
Each mole of glucose produces a fixed number of moles of products (from the coefficients in the model reactions).
Net ATP (both types)
\[
\begin{aligned}
n_{\mathrm{ATP}} &= 2\,n_{\mathrm{glc}}
\end{aligned}
\]
Lactic products
\[
\begin{aligned}
n_{\mathrm{lactate}} &= 2\,n_{\mathrm{glc}}
\end{aligned}
\]
Alcoholic products
\[
\begin{aligned}
n_{\mathrm{ethanol}} &= 2\,n_{\mathrm{glc}} \\
n_{\mathrm{CO_2}} &= 2\,n_{\mathrm{glc}}
\end{aligned}
\]
Converting grams to moles and back
If glucose is entered in grams, it must be converted to moles first.
In general:
\[
\begin{aligned}
n &= \frac{m}{M}
\end{aligned}
\]
where n is moles, m is mass (grams), and M is molar mass (g·mol−1).
Glucose conversion
\[
\begin{aligned}
n_{\mathrm{glc}} &= \frac{m_{\mathrm{glc}}}{M_{\mathrm{glc}}}
\end{aligned}
\]
Mass of products (optional output)
\[
\begin{aligned}
m_{\mathrm{product}} &= n_{\mathrm{product}}\,M_{\mathrm{product}}
\end{aligned}
\]
Carbon check (why it works)
A quick consistency check is that the total number of carbon atoms in products equals the 6 carbons in glucose.
This does not “prove” the pathway, but it is a good stoichiometric sanity check for balanced models.
Lactic fermentation
\[
\begin{aligned}
6 &= 2\cdot 3
\end{aligned}
\]
Alcoholic fermentation
\[
\begin{aligned}
6 &= (2\cdot 2) + (2\cdot 1)
\end{aligned}
\]
How to interpret the visualizations
-
Reaction flow diagram: shows glucose flowing to products and net ATP. Hover elements to see the computed amounts.
-
Products + ATP chart: compares amounts (in moles). For alcoholic fermentation, the “Products” bar is split into ethanol and CO2.
-
Zoom/pan: you can drag to pan and use Ctrl + scroll to zoom (or the zoom buttons).
Limitations of this simplified model
-
The calculator reports net ATP = 2 per glucose as the standard glycolysis yield and does not model ATP from oxidative phosphorylation.
-
It focuses on stoichiometry and scaling, not on intermediate enzyme steps or detailed NADH bookkeeping.
-
Real biological contexts can vary (organisms, conditions, and metabolite forms), but these yield relations are widely used for teaching.
