Unleash Your Inner Brewer: A Guide To Wild Yeast Beer

Wild yeast fermentations are an emerging trend in brewing that can provide a unique sensory experience for the consumer compared to beers brewed with commercial yeast strains. Wild yeast allows brewers to put a local story behind their beers by using strains isolated from the nearby environment. While wild yeasts can impart fruity, spicy, or sour flavors in beers without the addition of adjuncts, the beer’s sensory properties, yeast attenuation, and yeast’s alcohol tolerance are unpredictable, and evaluations must be conducted to determine the flavor profiles in beers brewed with wild yeast.

Obtain a single colony with a sterile inoculating loop

To obtain a single colony with a sterile inoculating loop, you will need to collect a sample of your choice from outside using a sterile scalpel and forceps (if needed). Examples of materials to collect include tree bark, flowers, and fruits. Tools may be sterilized with 70% ethanol, liquid no-rinse sanitizer, or by placing them in boiling water for 10 min. Place the sample in a broth tube and seal the tube. Place the tube into a shaking incubator at 30 °C (86 °F) at a moderate speed (e.g., 225 rpm) for 18–24 hr. As an alternative to a shaking incubator, the tubes can be held at room temperature and swirled occasionally to promote oxygen absorption into the media. However, the yeast may take longer to grow using this method, and may need to incubate as long as 48 hr.

Inoculate a fresh tube of broth

Obtain a single colony with a sterile inoculating loop and inoculate a fresh tube of broth. Place the tube into a shaking incubator at 30 °C (86 °F) and 225 rpm for 18-24 hours. Note: As an alternative to a shaking incubator, the tubes can be held at room temperature and swirled occasionally to promote oxygen absorption into the media. However, the yeast may take longer to grow using this method, and may need to incubate as long as 48 hours.

Place the tube into a shaking incubator

Once suitable yeast strains have been identified, they can be stored on agar plates for up to 6 months in the refrigerator by growing a liquid culture in the growth medium and performing a streak on a fresh agar plate. These steps should be repeated every 6 months to keep the yeast fresh and viable for brewing.

Obtain a single colony with a sterile inoculating loop and inoculate a fresh tube of broth. Place the tube into a shaking incubator at 30 °C (86 °F) and 225 rpm for 18–24 hr.

Note: As an alternative to a shaking incubator, the tubes can be held at room temperature and swirled occasionally to promote oxygen absorption into the media. However, the yeast may take longer to grow using this method, and may need to incubate as long as 48 hr.

Store inverted in a refrigerator until use, for up to 1 month. Discard plates if any growth occurs.

Maintain a sanitary environment

The most important considerations when growing wild yeast for beer are to maintain a sanitary environment and to properly prepare the media.

Tools may be sterilized with 70% ethanol, liquid no-rinse sanitizer, or by placing them in boiling water for 10 min.

Obtain a single colony with a sterile inoculating loop and inoculate a fresh tube of broth. Place the tube into a shaking incubator at 30 °C (86 °F) and 225 rpm for 18–24 hr. Note: As an alternative to a shaking incubator, the tubes can be held at room temperature and swirled occasionally to promote oxygen absorption into the media.

Store inverted in a refrigerator until use, for up to 1 month. Discard plates if any growth occurs.

The techniques described here outline the steps required to isolate and propagate wild yeast for brewing beer. Once suitable yeast strains have been identified, they can be stored on agar plates for up to 6 months in the refrigerator by growing a liquid culture in the growth medium (instructions above) and performing a streak on a fresh agar plate. These steps should be repeated every 6 months to keep the yeast fresh and viable for brewing.

Properly prepare the media

Maintaining a clean environment and properly preparing the media are the two most important considerations when it comes to isolating wild yeast for brewing beer.

Obtain a single colony with a sterile inoculating loop and inoculate a fresh tube of broth. Place the tube into a shaking incubator at 30 °C (86 °F) and 225 rpm for 18-24 hours.

As an alternative to a shaking incubator, the tubes can be held at room temperature and swirled occasionally to promote oxygen absorption into the media. However, the yeast may take longer to grow using this method, and may need to incubate as long as 48 hours.

Store inverted in a refrigerator until use, for up to 1 month. Discarding plates if any growth occurs.

Collect a sample of your choice from outside using a sterile scalpel and forceps (if needed). Place the sample in a broth tube and seal the tube. Place the tube into a shaking incubator at 30 °C (86 °F) at a moderate speed (e.g., 225 rpm) for 18-24 hours.

Frequently asked questions