| Fermentation | Fermentation | Aging | Aging | Organims | PH | |
| Temp | Time | Temp | Time | |||
| Beer | about two weeks | Weeks | yeast | 3.3-6 | ||
| lager (pils) | 7 to 13 °C | |||||
| ale | 20 to 22 °C | |||||
| Wine | about two weeks | weeks/month | yeast | 3-4 | ||
| red | 20-30 °C | 10 -12 °C | ||||
| white | 15 °C | 10 -12 °C | ||||
| Cheese | 29-31 °C | hours/ day | 10 -15 °C | Days /Weeks/Months | lab/yeast/fungi | 5 -6 |
| Bread | 5-30 °C | hours / days | – | – | lab/yeast | 5-6 |
| Yogurt | 45 °C | hours | – | – | lab | 4-4.5 |
Building up acidity ?
- Yeast also produces acids
- Organic acids are weak acids
- CO2 also becomes an acid in solution, carbonic acid
- Lactic Ph reduces the solubility of CO2
- Lactic acid (Pka 3.8), acetic acid (Pka 4.76)
- Lactic acid is ten times more acidic than acetic acid.
- The Ph is about the free proton concentration, i.e. how many protons are in solution. The Pka relates to the stability of a molecule, more specifically the ratio between the (de)-protonated fractions of the molecule.
More data yeas and LAB
- Saccharomyces genus (yeast) has an optimum at 32.3°C and stops growing at 45.4°C.
- L. sanfranciscensis stops growing at 41°C and C. milleri at 36°C, read more
LAB Growth stops arround Ph 3.6?
The inhibition of lactic acid production is due to the solubility of the
undissociated lactic acid within the cytoplasmic membrane and insolubility of dissociated lactate, which causes acidification of cytoplasm and failure of proton motive forces, read more
Why do we get more acetic acid on the long run ( fridge) Ph3.6 ?
Acetic acid in its undissociated form can cross the plasma membrane of S. cerevisiae. Once inside the cell, the undissociated acetic acid dissociates due to its pKa of 4.75 and the higher intracellular pH (pHi), causing intracellular acidification. read more
In our own words: lactic acid is larger than acetic acid, it forms more “quickly” during the metabolic breakdown of sugars. It’s higher acidity (lower Pka) helps these cells to more quickly acidify the extra cellular environment and compete with other microorganisms. To diffuse from the cell to the extracellular space acetic acid needs to be in its undissociated state. During favourable conditions the production of lactic acid seems the most logical way. But when conditions change the cell shifts to acetic acid which is more stable metabolic waste product (i.e. less acidic, higher Pka) increasing the chance it wil be able to diffuse over cel membrane. While lactic acid can be