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.

What is the Lacto Pitch Temperature Calculator?

Gives target pitch temperature ranges and souring time estimates for common Lactobacillus strains used in kettle sours and co-pitch sours. Includes a projected pH drop timeline based on strain and temperature. Runs 100% in your browser. It runs free in your browser on Gera Tools, with nothing uploaded.

Lacto Pitch Temperature Calculator

Name: Lacto Pitch Temperature Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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.

Why temperature matters so much

Lacto’s souring speed is not linear — it follows an exponential-style curve around its optimum. Drop 10 °C below the ideal band and souring that would take 12 hours might now take 48. This is why insulating the kettle or using a heat wrap is not optional for a same-day turnaround. Some brewers use a cooler filled with hot water to hold a small kettle overnight; others rig a heating element with a temperature controller. The goal is to stay within the stated band throughout the entire souring period, not just at pitch.

Equally important: high temperatures suppress contaminating organisms. Holding at 40–45 °C for L. delbrueckii makes the environment inhospitable to most spoilage bacteria that would thrive at room temperature, giving Lacto a competitive advantage even without an oxygen purge.

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.

Kettle sour vs. co-pitch: how temperature strategy differs

In a kettle sour, you hold the wort at souring temperature in the same vessel you will boil later. Speed is the priority — usually a target of pH 3.3–3.5 within 24–48 hours. Use the most thermophilic strain you can hold (L. delbrueckii at 43 °C if your setup allows) and aim for the upper end of its band.

In a co-pitch sour, you pitch Lacto first in the fermenter, let pH drop partway (often targeting around 3.8–4.2), then add yeast. Temperature compromise is required because the fermenter temperature will later need to suit the yeast. L. plantarum at 35–37 °C works well here as a middle ground.

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. Even cracking the lid to check pH introduces air, so minimise disturbance.
Pitch rate matters: underpitching Lacto slows the initial acidification phase significantly. Generous pitch rates (more is almost always better with Lacto) speed the early pH drop.
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.