MSc Project > Results & Dicussion: Impact of Temperature (LF1)
This post is part of a series detailing the findings of my MSc research project which looked at the effects of different fermentation parameters on wort souring with Lactobacillus. If you haven’t already, take a look at the MSc project page for a full overview.
In LF1 the effect of temperature on lactic fermentation was investigated using a culture of L. brevis WLP672. The fermentation parameters were outlined in Table 1.
In LF1 the effect of higher temperature was clearly apparent as both fermentations at 30°C and 37°C dropped the pH and increased acid concentration significantly faster and to a greater degree than at 20°C (Fig. 8A). Beginning at a pH of 5.03 ± 0.01 the pH dropped considerably during the first 24 h for both 30°C and 37°C, with a much steadier decrease at 20°C. For all temperatures the pH then displayed a constant but more gradual decline at 48 and 72 h. The final pH after 72 h at 20°C reached 3.74 ± 0.01, which was close to the 30°C and 37°C values (3.77 ± 0.02 and 3.67 ± 0.01, respectively) after only 24 h. Fermentation at 37°C resulted in the lowest pH and highest acid production at all time points, with a final 72 h pH of 3.41 ± 0.02 and acid production of 4.13 ± 0.12 g/L of LA (Fig. 8C). The difference between 30°C and 37°C was much less pronounced than from 30°C to 20°C. At 37°C the pH was 2.5% lower on average than at 30°C while the acid production was 12.4% higher.
The results demonstrated that L. brevis WLP672 could achieve respectable souring performance at both 30°C and 37°C. Considering that 37°C yielded a lower pH and higher acid production at all time points implies that it was closer to the optimal temperature for this strain (Fig. 8). This differed from the literature data available on L. brevis fermentation in wort, which, while very limited, suggested that 30°C was generally preferred. Peyer et al. reported that for both L. brevis L1105 and L. brevis R2Δ strains the optimal growth temperature was 30°C and that organic acid production was higher than at 37°C after 48 h.1 They did however note that while growth was lower, organic acid production was only very slightly reduced at 37°C compared with 30°C for the L. brevis L1105 strain. Wilson reported a similar result for L. brevis KD1 in 1.060 SG malt wort, stating 30°C was the optimum growth temperature after 24 h and a substantial decline was observed above 35°C.2
Although the souring potential of L. brevis WLP672 was found to be highest at 37°C, it’s worth noting that growth was not actually measured at this temperature, so the correlation between growth and acid production is not known in this case. Optimal temperatures can vary widely within both the Lactobacillus genus and L. brevis species and are generally considered to be strain dependent.3 Numerous studies have also shown that LAB behaviour can be modulated by a huge range of factors. Both aeration and oxygen content of the medium, which were not controlled in this study can have a profound influence on Lactobacillus growth and metabolism.4, 5 The methods of production and properties of wort have also been found to have a dramatic impact on acid production. For example, grist composition and mashing regime can be manipulated to alter parameters such as pH and buffering capacity as well as determine the carbohydrate concentration and nutrient availability, all of which can affect acid production by LAB.6
- Peyer, L. (2017) Lactic acid bacteria fermentation of wort as a tool to add functionality in malting, brewing and novel beverages, School of food and nutritional sciences, University College Cork, Cork, Ireland.
- Wilson, N. R. (2008) Effect of lactic acid bacteria on congener composition and sensory characteristics of scotch malt whisky, School of life sciences, Heriot-Watt University, Edinburgh, UK.
- Pot, B., Felis, G. E., De Bruyne, K., Tsakalidou, E., Papadimitriou, K., Leisner, J., Vandamme, P. (2014) The genus Lactobacillus, in Lactic acid bacteria biodiversity and taxonomy, (Holzapfel, W. H., Wood, B. J. B. Eds.) pp. 249-354, John Wiley & Sons, Ltd, Chichester, UK.
- Stamer, J. R., Stoyla, B. O. (1967) Growth response of Lactobacillus brevis to aeration and organic catalysts, Appl. Microbiol., 15, 1025.
- Quatravaux, S., Remize, F., Bryckaert, E., Colavizza, D., Guzzo, J. (2006) Examination of Lactobacillus plantarum lactate metabolism side effects in relation to the modulation of aeration parameters, J. Appl. Microbiol., 101, 903-912. https://doi.org/10.1111/j.1365-2672.2006.02955.x
- Peyer, L. C., Bellut, K., Lynch, K. M., Zarnkow, M., Jacob, F., De Schutter, D. P., Arendt, E. K. (2017) Impact of buffering capacity on the acidification of wort by brewing relevant lactic acid bacteria, J. Inst. Brew., 123, 497-505. https://doi.org/10.1002/jib.447