Ancient Mead Making Meets Modern Science
Part 2: Isolating a Pure Yeast from a Wild Honey Culture (Honey Bug)
This article is the second of a series that combine the ancient ways of making mead with modern science. The first article demonstrates how to generate a wild yeast culture from honey (honey bug). The second article teaches a method for purifying a pure yeast strain that specializes in making mead from the honey bug. These two guides will allow you to generate an authentic “mead yeast” directly from honey!
After your personal house mead yeast is generated, the next series of articles will focus on ancient mead recipes for your newly generated mead yeast. As usual, I will use scientific methods to research and update the approach to these ancient recipes.
Better mead making through science!
1. Honey Bug – See previous article.
2. Jar with a lid – Mason jars are great for this.
3. Bottled spring water – NOT distilled water
4. Metal flame loop – Amazon
5. Malt Extract Agar (MEA) Plates – Amazon
6. Torch – Any home improvement store
7. Fermaid O or K – www.morewinemaking.com
Single Strain Yeast Isolation
In the first article, Ancient Mead Making Meets Modern Science Part 1: Wild Yeast Culture from Honey (Honey Bug), we generated a wild yeast culture from honey or a honey bug. Here, I will explain how to isolate a single strain of yeast from your multi-strain honey bug culture. I know it sounds daunting, but this method is really simple once you understand it. I’ve even included pictures here so that you know what it is supposed to look like!
Starting with your honey bug, you should have a fluffy layer of yeast on the bottom of your culture (See picture for an example) and a mat of fungus on top. If you cannot see any yeast accumulated on the bottom, then the culture probably isn’t ready for isolation. Wait longer until you can see the yeast sediment to improve your chances for a successful isolation. From this culture, we begin our honey yeast isolation.
Example of a yeast layer at the bottom
1. Use the torch to get your flame loop red hot (use the lowest setting your torch can sustain to avoid destroying your loop). Pull the top mat of fungi to the side. Flame your loop again. Use the loop to get a small amount of yeast off the bottom.
2. Streak the multi-strain yeast mixture on a Malt Extract Agar plate using the four quadrant streak method (Instructions here halfway down the page).
3. Store plate at room temperature 24-48 hours.
4. You will see lots of different microorganisms on the plate. Yeast will appear as small, smooth, white round colonies. You will likely see other contaminating microorganism such as fuzzy-looking filamentous fungi.
Mixed culture on a Malt Extract Agar plate
5. Pick one well isolated yeast colony and re-streak on a new plate. To ensure you get a good yeast or different strains of yeast, you can streak multiple single colonies on separate plates.
6. Repeat step 5 until you only see one type of colony on the entire plate.
Pure honey yeast strain on Malt Extract Agar
Honey Yeast Isolate Testing
Once you have a pure strain of yeast, you must test the yeast to determine if it has good qualities in mead. Some strains of yeast are naturally unsuitable and produce rancid flavors while others intensify the honey notes. I even have one strain that smells like honey on the agar plate!
1. Inoculate a small starter in a sanitized jar to test the characteristics of your new yeast as follows:
-1/5 cup honey
-4/5 cup spring water
-1/2 tsp Fermaid O or K
-1 colony of your honey yeast isolate. Use the pre-flamed, pre-cooled loop for this.
2. After a week, taste for any extremely off flavors.
3. If the characteristics are good, inoculate a larger batch. If not, start over.
4. Bank the yeast in a yeast bank for long term storage (See Yeast Bank article).
Pure honey yeast starter. Notice there is no longer mold on top!
Generally, wild yeast have two phases of fermentation. The first phase is a mixture of low and high alcohol tolerant yeast. Once a sufficient amount of alcohol is produced, the low tolerance yeast dies off and the high tolerance yeast takes over. For isolation purposes, you generally want to wait until the mead has hit 10% ABV or higher before you attempt isolation so that you get the highly tolerant strains. Alternatively, you could attempt to isolate the low ABV tolerant yeast strains from the early culture. It is your choice.
When we streak the mixed population on the plate, we are dragging the yeast and other organisms until only single cells remain. In microbiology theory, this dilutes the organisms such that only one remains to generate each colony. We then pick an isolated colony and streak again for single microbe isolation. After multiple rounds of this, we are left with a pure strain of yeast than originates from a single yeast cell. This process is the entire basis of microbial isolation technique. All the yeast you purchase from the home brew shop was isolated this way!
Yeast from this isolation process can be extremely good or extremely bad. Don’t be discouraged if your first isolate doesn’t work out. I’ve had a few fails as well, but the successful strains more than make up for the failures. Isolating multiple single colony isolates can improve your chances greatly. You had to buy a stack of Malt Extract Agar plates anyway…
Happy mead yeast hunting!