Bottling and Headroom (Updated July 12, 2010)

***For the update please scroll down to the bottom of this post***

After several readers inquired about leaving headroom when bottling, I felt obligated to experiment.

I had always learned to fill the kombucha all the way to the top when bottling for a secondary fermentation. This stops the activity of the bacteria because of the exclusion of oxygen, while the yeast can continue to ferment the sugars to create CO2 and an effervescent drink, because yeasts can function with or without oxygen (1).

After being prompted to do some experimenting on my own, I left around an inch of headroom in several kombucha bottles for a secondary fermentation. I left the bottles out for a few days, and then I refrigerated them. I didn't open the bottles right away because I already had some kombucha bottles open, but I pulled one out from the refrigerator a week or so later and found that the kombucha bottled with around an inch of headroom was more fizzy than a good number of my previous batches!

Bottling with Headroom
Photo courtesy of Haven Sarah Ripley Daniels

Although Happy Herbalist mentions to fill the kombucha to the top of the bottles in their Brewing Guide (look under "Bottling"), on their Bottling Tips page there is a section "Choosing to leave an airspace." According to their Bottling Tips page, if you leave oxygen and airspace in the bottle and if the temperatures are between 70-85 degrees F, the bacteria will continue to remain active and the kombucha will continue to sour, which makes sense because the bacteria require oxygen.

Meanwhile, the yeasts can function with or without oxygen. However, according to Happy Herbalist, yeasts only form carbon dioxide and fizz when oxygen is present (2). "Carbon dioxide suffocates/diminishes the bacteria, but produce[s] the fizz and sparkling brew. Without oxygen the yeast produce more alcohol...The yeast may be active in temperatures as low as 40F (5C) with or without oxygen" (2). In other words, if you leave headspace when bottling, the yeasts can create more carbon dioxide and fizz because of the oxygen present in the airspace. But if there is no airspace, the ability of the yeasts to produce an effervescent drink is limited because of the limited availability of oxygen.

Unfortunately, I was perfectly happy with this explanation until I returned to this formula from my previous post, Kombucha + Fizz, and could not find oxygen needed in the equation for the yeasts to form carbon dioxide:

The yeasts convert sugar to alcohol + carbon dioxide (3, p. 40)

C6H1206 -> 2C2H5OH + 2CO2
sugar -> alcohol + carbon dioxide

Thus, I am somewhat still confused about the exact relationship between the yeasts, oxygen, carbon dioxide, and kombucha fizz. Perhaps the presence of oxygen helps to encourage the yeasts to form more carbon dioxide and fizz, but its presence is not necessary?

Something to note is that kombucha that is bottled all the way to the top will taste different than kombucha that is bottled with airspace, such as in the amount of fizz produced and in others ways as well, such as the acidity of the drink.

I have not found much information on the recomended amount of airspace if you decide to bottle kombucha this way. However, beer brewers tend to leave 1-2 inches of headspace in their bottles according to this thread. Again, experimentation is key, and do whatever you prefer according to personal preference and taste!

As always, I am continuing to learn more about kombucha day by day, and I hope to share that information. If you have any more information or tips on the bottling process and kombucha fizz, please send the information my way or leave a comment!

All my posts related to bottling can be found here.

References
1. http://www.happyherbalist.com/brewing_kombucha.htm
2. http://www.happyherbalist.com/bottlingtips.aspx
3. Frank, Gunther W. Kombucha - Healthy beverage and natural remedy from the Far East. 4th ed. Austria: Wilhelm Ennsthaler, 1994.

***Update July 12, 2010***

I was able to get to talk to a brewer who brews beer and kombucha. Here is what I learned:

• Confirmation that headroom helps prevent the bottle from exploding from the buildup of carbon dioxide.
• You can still increase the fizz in your brew whether or not you leave headroom in your bottle.
• You won't lose fizz by leaving headspace in the bottle.
• You lose more fizz the more you transfer the kombucha from container to container. You can actually decarbonate your brew by transferring your kombucha from container to container.

In this article from Happy Herbalist, it states that aerobic and anaerobic yeasts in kombucha help to produce carbonation, and that the production of more carbonation than alcohol by both types of yeast is favored when oxygen is present, which is in line with the other Happy Herbalist information (that I am conflicted about) that I provided above.

Part of the reason why there doesn't seem to be a clear answer to the question about whether it is better or not to leave headroom to create more fizz, is because kombucha ferments and SCOBYs contain different strains of bacteria and yeasts and in different proportions. Wild and airborne bacteria and yeasts, which differ according to the location and environment, add even more variation to the mix. Here is one Analysis of a Kombucha Ferment by Happy Herbalist as an example for what may be in your brew.

I personally prefer to bottle with headroom at the moment. But it is up to you, and based on your experiences, to decide whether or not you want to leave headroom in your bottles. I recommend experimenting with both. If anyone wants to share their experiences with bottling, please do so!

Kombucha + Fizz (Updated May 27, 2010)

Yes, kombucha can be fizzy.

I've been receiving numerous questions about fizz, so here is what I understand thus far on the matter!

To begin, fizz does not indicate the health of your SCOBY or your ferment. Fizz is more a matter of personal preference, and may indicate the balance of yeasts and bacteria in your brew (1, 2).

For the scientific side on the matter, here are the chemical reactions that occur during kombucha fermentation (3, p. 40):

The yeasts convert sugar to alcohol + carbon dioxide.

C6H1206 -> 2C2H5OH + 2CO2
sugar -> alcohol + carbon dioxide

The bacteria convert the alcohol to organic acids, such as acetic acid, and water.

C2H5OH + O2 -> CH3COOH + H20
alcohol + oxygen -> acetic acid + water

The CO2 (a gas) that forms reacts with the water in the tea to produce carbonic acid (think of carbonic acid as dissolved CO2). Carbonic acid is a weak acid that readily decomposes back into water and carbon dioxide. When the carbon dioxide bubbles out of the water, you get fizz (4).

CO2 + H2O -> H2CO3
carbon dioxide + water -> carbonic acid

Carbonation and the primary fermentation:
As the new kombucha mushroom forms at the surface during fermentation, the ability for the carbon dioxide to escape decreases, helping to create some of kombucha's natural fizz. The more quickly and the more thick your mushroom forms, the less the CO2 will be able to escape, which can increase the carbonation of your drink (3, p. 33, and 5).

A lower fizz may indicate a lower ratio of yeast to bacteria in your culture. The ratio of yeasts in your brew may be increased by (1):

• Using the bottom SCOBY from your previous batch
• Using more of the kombucha at the bottom of your brew, which tends to be more cloudy/yeasty, for your starter tea.

Carbonation and the second fermentation:

• Fizz can be significantly increased by bottling. My posts related to bottling can be found here.
  
• Consider experimenting with leaving and not leaving airspace. Read my post Bottling and Headroom.
  
• Adding flavors (such as jams, citrus peels, ginger, etc.) during the bottling process can also help to create more fizz. (Similar to adding a primer in beer making).
  
• Beer bottles, which have a very tight seal, are ideal for creating fizz in kombucha. In my experience, when I've used resealable bottles (such as GT's or Katalyst kombucha bottles), I've lost more fizz.
• -The longer you leave your bottles out for a secondary fermentation, the more carbonation will build up. HOWEVER, if you leave your bottles out for too long, you run the risk of them exploding! Some people recommend 1-2 days for a secondary fermentation, others 3-4 days, and some recommend even longer. It all depends on various factors, including the sugar content of your kombucha and the temperature (higher temperatures = faster fermentation).
  -My advice: If you're fermenting a batch, try a bottle after 1 or 2 days (more or less days depending on previous experiences, etc.). Then decide whether your other bottles are ready to refrigerate, or if they could use some more time fermenting.

Some more reading:

• Kombucha Balance on No fizz, Too much fizz, Increasing the ratio of yeasts, and Increasing carbonation
  
• getkombucha: The Fizz Factor #1
• A great thread that discusses fizziness and beverages
  
• Although there is limited information on kombucha and fizz, there is extensive information about carbonation and beer making on the web. Although beer and kombucha are clearly different drinks, they are similar in that they are both fermented beverages. Perhaps looking up beer carbonation will provide more clues as to factors that affect kombucha fizz? Try here and here for starters.

Happy brewing!

Sources:
1. http://users.bestweb.net/~om/kombucha_balance
2. http://www.getkombucha.com/spreisfifa1.html
3. Frank, Gunther W. Kombucha - Healthy beverage and natural remedy from the Far East. 4th ed. Austria: Wilhelm Ennsthaler, 1994.
4. http://uk.answers.yahoo.com/question/index?qid=1006051206579
5. http://kombuchakamp.blogspot.com/2009/04/fizzy-brew.html

Broken Glass

As I was washing the dishes one day, I heard a slight crack. I looked around the kitchen but didn't notice anything...but soon the smell of kombucha filled the room. Uh-oh.







It turns out, a bottle of my kombucha had exploded- as a kind reminder not to leave your kombucha bottles out for too long for a second fermentation.






I have been fortunate to have never had a bottle of kombucha explode on me before this day, and after brewing kombucha for over a year, I guess it was about time.

Luckily, the explosion was a lot less dramatic than it could have been. When I first began bottling kombucha, I had been nervous about shards of glass ending up on on my wall.

Tips to avoid kombucha bottle explosions:

-As mentioned in my previous post, Kombucha + Fizz:

• Beer bottles with their narrow necks and tight caps are ideal for creating fizz, and the longer you leave your bottles out for a secondary fermentation, the more fizz will build up. HOWEVER, if you leave your bottles out for too long, and especially with such tight seals, you run the risk of them exploding. Some people recommend 1-2 days for a secondary fermentation, others 3-4 days, and some recommend even longer. It all depends on various factors, such as temperature (higher temperatures = faster fermentation).
  
• My advice: If you're fermenting a batch, try a bottle after 1 or 2 days (more or less days depending on previous experiences, etc.). Then decide whether your other bottles are ready to refrigerate, or if they could use some more time fermenting.
  
• If you can hear your kombucha bottles at room temperature fizzing, refrigerate it!!
  

**Please note that this graph is not to scale whatsoever, and was merely created in order to illustrate a concept.**

***The longer you leave your kombucha bottles out for a second fermentation, the more fizzy your kombucha, but the more risk you will have of your bottles exploding. Experimentation and practice are key!***

-Read this discussion thread on bottling technique from some fellow kombucha fermenters.

• According to this thread, flip-top beer bottles can be a good option, because the rubber seal releases some of the pressure that may cause your bottle to explode.

Adding to my list of broken kombucha bottles includes one instance when my refrigerator somehow got to freezing temperatures, causing the kombucha to freeze and expand (when water freezes into ice, the volume expands as the molecules form a crystal lattice), causing another kombucha bottle to break.





At the time I decided to take an artistic approach to the situation, resulting in this photo:

Kombuch-sicle, anyone?

Home-brewing (and in fact, brewing in general) is never perfect. Accidents happen, but they are all part of learning how to brew and how to perfect your technique, and make your home-brewed kombucha that much more worthwhile. What interesting kombucha experiences have you had?