What temperature should I pitch Lactobacillus at?

It depends on the strain. Thermophilic strains like L. delbrueckii prefer 40 to 45C, while L. plantarum is happy around 35 to 40C and many L. brevis blends work from 30 to 35C. The tool shows the band for the strain you pick.

Why does temperature change souring speed?

Lactobacillus is most metabolically active near the top of its range, so holding wort warm dramatically speeds lactic acid production. Drop 5 to 10C below ideal and souring can take days instead of hours.

What pH should a kettle sour reach before boiling?

Most brewers target pH 3.3 to 3.5 for a clean, assertive sourness before they boil to kill the Lacto and proceed with a normal fermentation. The tool projects time to reach 4.5, 4.0, and 3.4 so you can plan.

Should I purge oxygen when souring?

Yes. Lactobacillus sours fastest and cleanest in low-oxygen conditions, and oxygen exposure encourages off-flavours and unwanted microbes. Purge headspace with CO2 and minimise splashing during transfer.

Can I co-pitch Lacto with yeast instead of kettle souring?

Yes, a co-pitch or sour-worting approach pitches Lacto first to drop the pH, then adds yeast. The temperature guidance here still applies for the souring phase, though co-pitch sours usually run cooler and slower than a hot kettle sour.

Lacto Pitch Temperature Calculator

Souring wort with Lactobacillus is fast but temperature-sensitive. This tool gives you the ideal pitch temperature band for common strains, tells you whether your kettle temperature is in range, and projects how long it will take to reach the pH targets that matter for a kettle sour or co-pitch sour.

How it works

Each Lactobacillus strain has an optimum temperature range where it is most active. The tool stores typical bands and a base souring rate for the most-used strains:

L. delbrueckii — thermophilic, 40 to 45 °C, very fast and clean
L. plantarum — 35 to 40 °C, fast, low diacetyl, widely available
L. brevis — 30 to 35 °C, robust, slightly slower
L. buchneri / blends — 32 to 38 °C, moderate

The souring timeline is modelled from a base rate at the strain’s optimum, scaled by how close your kettle temperature is to that optimum. Holding warmer (within range) speeds the pH drop; holding cooler slows it. The wort starts near pH 5.2 and the tool reports the projected hours to reach pH 4.5, 4.0, and 3.4.

Reading the result

If your temperature sits inside the strain’s band, you get the fastest clean souring. The tool flags an out-of-range temperature so you know to insulate the kettle, use a heat belt, or pick a strain better suited to what you can hold.

Tips and notes

Pre-acidify the wort to around pH 4.5 with food-grade lactic acid before pitching; it suppresses competing bacteria and gives Lacto a head start.
Purge the headspace with CO2 and keep the wort still — Lactobacillus sours best with minimal oxygen.
Taste and check pH rather than relying on the clock alone; gravity, buffering, and pitch rate all shift the real timeline. These figures are planning estimates and run entirely in your browser.