This post is a follow up to Kombucha Bubbles: How to Increase Carbonation…for Beginners. If you are looking to increase your fizz factor while brewing Kombucha, try those techniques first and if you are still unable to achieve the carbonation you are looking for, only then try those listed below.
These methods are intended for the more experienced Kombucha brewer and even then only for those who have extra cultures to experiment with. I recommend using one method at a time to see how it works and avoid over yeasting your brew.
First though, to understand what we want to accomplish, let’s take the opportunity to more deeply explore the yeast/bacteria symbiotic relationship!
The Yeast/Bacteria Relationship
The bacteria and yeast in the starter culture work in symbiosis to transform tea and sugar into fermented Kombucha tea. The yeast consume the sugar and create ethanol (alcohol) and carbon dioxide (our fizz factor!), then the bacteria consume the ethanol and convert it into healthy amino acids.
The balance between the yeast and bacteria can be a delicate one. If there is too much yeast in your brew, it can cause the bacteria to struggle; the other way around and your brew has little to no fizz. As always in life, strive for the ideal balance for optimum results.
Symptoms of an unbalanced Kombucha brew that may need a yeast boost:
Kombucha sours slowly or takes too long to reach the desired tartness
Little SCOBY growth
Lack of carbonation
What is Yeast?
Yeasts are single celled organisms that have been used in baking and fermentation for thousands of years. They belong to the kingdom Fungi (Kombucha is not a mushroom, people!).
Each Kombucha culture has its own variety of bacteria and yeast; though all of them will have acetobacter and saccharomyces, the exact composition may vary. Some of the common strains of yeast in the culture include: Saccharomycodes ludwigii, Saccharomycodes apiculatus, Schizosaccharomyces pombe, Zygosaccharomyes & Saccharomyces cerevisiae.
DID YOU KNOW? “Saccharomyces” is derived from Latinized Greek – saccharo- “sugar-” and myces “fungus”. Cerevisiae comes from Latin and means “of beer.” Cerveza anyone?
The yeast are the brown strands or strings that you find floating attached to the culture or collecting at the bottom of the jar. They thrive at lukewarm to mildly warm temperatures which is the reason why the tea solution must cool prior to adding the culture. Too hot and they die off. Yeast release CO2 and ethanol. It is the CO2 causes bread to rise and gives beer and Kombucha its natural fizz. Roll up your sleeves and let’s go yeasting!
Warning: Remember, Kombucha bottles may explode if left unattended. Kombucha CO2 can build up quickly, especially with these techniques. Bottles must be monitored and burped, and it is recommended that one takes extra care when using these techniques as the increase in yeast activity can be significant. Store your secondary ferment bottles in a cooler, box or small enclosed cupboard to prevent additional damage. While I have never experienced an exploding bottle, I have heard the stories.
Yeast Manipulation Techniques for Increasing Carbonation
Take Starter Liquid From the Bottom
Yeast is distributed throughout the Kombucha, whether you can see it or not. Once the yeast have done their job, they collect at the bottom of the brewing vessel. When they join together, they form the brown strings you see in the photo.
Normally, in order to preserve a healthy balance of bacteria & yeast, the starter liquid is pulled from the top. This ensures that we don’t over yeast the brew (a lesson I learned the hard way).
However, if we are looking to boost our yeast quotient, the best place to find them is hanging out towards the bottom, which makes gathering them much easier. Here’s what you do:
- Pull 2 cups of yeastie starter liquid from the bottom of your brewing vessel.
- When you have completed your brewing process (use 1 cup less water to accommodate the extra starter liquid), add the yeastie starter as the last step.
- Cover and if possible place near a source of warmth (heating mat, warm stove, in a crock pot on low, etc) to keep the yeast active.
- You should notice more carbonation within 1-2 brewing cycles.
Increase the Amount of Tea
The caffeine present in the tea will stimulate the yeast to remain active rather than allowing them to take their normal rest cycle. Add an extra teaspoon or two (1-2 tea bags) of green or black tea to achieve the desired result. Green tea has been noted for its ability to boost carbonation but my experience has shown me that the culture prefers a variety of teas to thrive – so don’t be afraid to mix it up. Check out this blog post for more information on the best teas to use for fermenting Kombucha.
This technique is described by Len Porzio of Balance Your Brew. I have never tried this method: mainly because I go with the flow – sometimes my brew is super bubbly and other times it is more flat and I’m cool with that. Len is a muy respected Kombuchero, so let’s see how his method works:
- Filter the fermented KT with a cheesecloth into a plastic bottle (a 2 Liter soda bottle works great for this) – you don’t want to prevent all of the yeast from getting through, this is just to remove the ooglies.
- Fill the 2-liter bottle all way to the rim with the KT.
- Gently squeeze the bottle to remove excess air before capping.
- Allow the bottles to remain at room temperature.
- Check the amount of carbon dioxide pressure building up by squeezing the bottle. You want it to feel hard, like a basketball. This process usually takes 1-2 days but may take longer if yeasts are lacking.
- Once your bottles are hard, transfer them to the fridge to deactivate the yeast (go dormant) and reduce the amount of pressure that has built up.
- After a couple of days in the fridge, gently pour the liquid into glass bottles. You should notice fizzy bubbles as you pour, but do not pour so fast that it froths in the bottle.
- Take care not to allow the spent yeast that has collected on the bottom to enter the bottles. Discard the spent yeast.
Len sez: Don’t Forget: Fill your bottles up to the rim & sample your brew when pouring from plastic to glass- if too tart, add some sugar or agave to mellow the flavor.
The Crabtree Effect is not an overpriced soap store or a bad 70’s action picture. In fact, The Crabtree Effect is a normal part of the Kombucha brewing process. It occurs when an excess amount of glucose (sugar) is introduced too quickly to the yeast.
Much like a typical family after Thanksgiving dinner, the yeast fall into a “food coma” and stop reproducing. Usually, this is great as it allows the bacteria to kick into gear and maintain balance. However, if we want the yeast to keep working, we need to prevent The Crabtree Effect from occurring.
To prevent your yeast from passing out on the job, gradually add the normal amount of sugar over the course of three days. This allows the yeast the chance to keep up with the amount of glucose present in the nutrient solution.
Here’s what ya do (all measurements based on 1 cup of sugar per gallon of nutrient solution, scale to fit your needs):
- Day 1, add 15% of the sugar = 2-1/2 tablespoons
- Day 2, add 30% = 1/3 cup
- Day 3, add the remaining 55% = 1/2 cup + 1 tablespoon
Now you’ve got loads of tips and tricks to try next time you are feeling like your brew is falling flat.
Have you tried any of these techniques? Did you get loads of carbonation? Have other tips for boosting the bubbles?
Share your story in the comments below =)