Beer fermentation: the phases of the curve in a 2024 study
A study by the University of Salerno and the University of Brescia describes the three phases of beer fermentation and what happens with less yeast. The extract curve in MicroDens Logger Pro.
A study published in 2024 in the journal Fermentation by researchers at the University of Salerno and the University of Brescia followed the fermentation of six types of beer in a microbrewery and of two batches in the laboratory.
Three phases
The authors divide the alcoholic fermentation of beer into three phases, each recognizable from the rate at which the process advances.
The production trials took place in a microbrewery in the province of Salerno, in 150 L cylindrical fermenters with 90 L batches, in a fermentation room at 16 °C. The six beers differed in recipe and original gravity. In all the batches, followed for six days, the three phases were recognizable.
The beers in the study
Original gravity (OG) and final gravity (FG) of the wort in °Plato, calculated from OG and FG with the ASBC formula; in brackets the specific gravity reported in the study, measured with a density meter with 0.001 g/cm³ resolution.
| Beer | OG | FG |
|---|---|---|
| Lemon Ale | 9.0 °P (1.036) | 2.6 °P (1.010) |
| British Golden Ale | 11.2 °P (1.045) | 2.6 °P (1.010) |
| Apple Wit Ale | 11.9 °P (1.048) | 2.6 °P (1.010) |
| Belgian Pale Ale | 13.3 °P (1.054) | 3.6 °P (1.014) |
| English IPA | 14.3 °P (1.058) | 3.1 °P (1.012) |
| British Strong Ale | 17.7 °P (1.073) | 4.6 °P (1.018) |
The same wort with less yeast
In the laboratory the authors set up two fermentations with the same wort, made from 4 kg of liquid malt extract and 20 L of water, with an original gravity of 13.3 °P (OG 1.054) and the same yeast strain. Only the amount of yeast pitched was different.
Reference batch
Known recipe, brewed according to good brewing practice. Final gravity reached: 3.6 °P (FG 1.014).
Under-pitched batch
Markedly slower fermentation. The final gravity was not reached: fermentation remained incomplete.
For the authors this is an example of how the course of fermentation, observed while it happens, shows whether a batch is progressing as it should. Among the next steps they mention alarm thresholds, derived from data on new recipes, to flag a problem to the brewmaster in good time.
Fermenter weight and wort density
The study starts from an observation about the sector: microbreweries are mostly small companies that often cannot afford the monitoring systems built into the plants of industrial breweries, yet they still need to control the process to keep the quality of their beer consistent.
The proposed system weighs the fermenter. During fermentation the yeast converts sugars into alcohol and carbon dioxide, which escapes through the airlock on the lid: the weight drops, and the rate at which it drops distinguishes the three phases. To compare weight and density, in one laboratory trial the researchers took samples from the fermenter during the process and measured their density with a triple-scale hydrometer, finding a linear relationship between the two.
The extract curve
With traditional methods, the authors note, fermentation is followed by periodic sampling. With a density meter, the curve is built from the density of the samples: the original gravity of the wort is the starting point, and the apparent extract in °Plato falls during fermentation and settles at the final gravity.
Each reading on the fermenter curve
The MicroDens portable density meter follows fermentation with the BeerQuick method, without distillation: the wort reading sets the original gravity, and each subsequent reading of the fermenting beer updates the estimates of alcohol and attenuation.
MicroDens Logger Pro, Fermentation module
In MicroDens Logger Pro, the Gibertini Elettronica software for the MicroDens density meter, the Fermentation module plots each BeerQuick reading on the curve of the fermenter with the same original gravity. The apparent extract curve runs from the OG of the wort to the final gravity and shows the lag, active fermentation, slowdown and end phases. The current batch can be compared with up to five earlier batches of the same method, with the curves aligned from the start; from the curve of a reference batch or from the trend of the last 24 hours the software estimates the final gravity and the remaining time, with a confidence rating.
°P
Apparent extract, from OG to final gravity
4 phases
Lag, active fermentation, slowdown, end
5 batches
Compared with the current one
±0.0001 g/cm³
Density accuracy, MicroDens
- D. Buonocore, G. Ciavolino, S. Dello Iacono, C. Liguori, "Online Identification of Beer Fermentation Phases", Fermentation 10(8):399, 2024 (open access). The °P in the table are calculated from OG/FG with the ASBC formula.
- MicroDens Logger Pro, software page: Fermentation module.
- MicroDens for beer: BeerQuick method and density accuracy.
Last updated: November 3, 2026