SCOBYs under the microscope

Introduction

With origins dating as far back as 300 BC in northeast China, Kombucha tea has recently grown in popularity as a delicious and bubbly probiotic drink with many acclaimed health benefits. While you can typically find it available from grocery stores for $2/ pint, few people know that kombucha is easy to brew at home, requires very few ingredients, and offers many perks over buying it in the store. Not only is it substantially cheaper home-brewed, but you get to control the flavor (think fruits and herbs!), and strength of the fermentation of the brew to your liking (depending on how many days you allow the culture to brew).

Let’s talk SCOBYs!

To brew your own boocha, you simply need green or black tea, a sweetener (white sugar or honey) and a SCOBY (symbiotic culture of bacteria and yeast). We can attribute the magic of the fermentation process to the bacteria and yeast which consume the sugar in the tea to produce carbonation. The SCOBY, also common called the ‘Mother’ culture, is cellulose-based biofilm or microbial mat found floating at the container’s air-liquid interface, pictured below. Based on the desired product of the SCOBY, different species of bacteria and yeast are used. Such cultures generally include aerobic, gram negative AAB species such as Acetobacter , Gluconobacter and Komagataeibacter , aerobic, gram positive LAB such as Lactobacillus , as well as various yeasts such as Saccharomyces and Zygosaccharomyces .

Pictured here is a typical brew of komucha which will have the SCOBY floating at the air-liquid interface. The new SCOBY growth occurs at the top while yeast growth extends down into the liquid.

Once the SCOBY has been placed in the sweetened tea in a warm environment (65-75F), the magic of kombucha brewing centers around the first step of the fermentation which enlists the metabolic powers of the yeast to convert the sugars (such as glucose) from black or green tea into ethanol and carbon dioxide. The second step in the formation of SCOBY is the bacteria’s role in the culture to convert the ethanol product of fermentation into organic acids such as lactic acid or acetic acid. These processes are known as lactic acid fermentation and ethanol metabolism respectively. Once the brew reaches a desired fermented taste, the carbonated beverage can then be re-sweetened with your favorite fruit juice or puree, or enjoyed by itself!

Are all Kombuchas created equal?

My thought has always been – are all kombuchas created equal? When looking at the ingredient list (pictured below), there’s a whole array of juices or sweeteners that companies will add to their kombuchas to make them taste good. There’s no accountability or “grading” system to help consumers understand how diluted these drinks are or how much of the SCOBY’s fermentation byproducts are present in any bottle.

This is when I decided to dive into the microcosmos to figure out for myself if I could see the yeast and bacteria present in these bottles to serve as a proxy for the quality and concentration of kombucha in the drink. Can I see the bacteria or yeast present in these drinks? Is there large variation between drinks? How would my pure kombucha home-brew compare to store-bought drinks with juices mixed in?

Methods

I went to my local Trader Joe’s and bought each of the kombucha brands available to compare against my homebrew. Pictured below, I purchased the following brands for evaluation:

1. Revive Kombucha: Original Cola flavor
2. Brew Dr Kombucha: Clear Mind flavor
3. Health-Ade Kombucha: Pink Lady Apple
4. Synergy raw kombucha: Gingerade flavor
5. My home brew kombucha

I first wanted to understand what the SCOBY, the source of the probiotic yeast and bacteria, looked like.

From my brew (picture below), I removed a small section of the mother SCOBY, extracting both an area of yeast strand and a portion of the cellulose colony (pictured below). I then imaged my home brew to understand what pure kombucha would look like before moving onto the store-bought boochas!

Results

After loading these samples onto the foldscope, I captured these images of the cellulose and yeast areas of the SCOBY.

Home brew images

I then moved onto my home-brewed kombucha. I considered this the control since it is pure, undiluted kombucha. Here are the results of what I saw beneath the foldscope of my kombucha brew!

Revive Kombucha

First up of the bottles was revive Kombucha. As indicated by the arrows in the images below, small traces of yeast could be found, but were rather sparse. I didn’t find any traces of bacteria.

Brew Dr Kombucha

Again here I was able to find a few instances of what looked to be yeast. However, these were the only two examples, so again rather sparse.

Health-Ade Kombucha

Next up was Health-ade Kombucha. This is one of my favorite brands and flavors of Kombucha, so I was nervous what I’d find! Unfortunately, I wasn’t able to find much – only some traces of structures that may be bacteria? But definitely not very pronounced.

Synergy Raw Kombucha

This is by far one of my favorite brands and was definitely one of the earliest Kombucha brands to come on the market. I remember when it was largely the only option available in the grocery store and the brand that got me interested in brewing!

I was so excited to see what was not only a strong yeast showing, but what seemed to be clear examples of bacteria scatter throughout the entire field of view! Even more pronounced than in my home-brew.

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Conclusions

In an effort to understand if there’s a discernable difference in quality of kombuchas which may be diluted by fruit juices or other sugars, I scanned several store-bought brands for semblances of bacteria and yeast which are the main components of a prolific SCOBY.

In comparison to my home brew which I used as control since I did not add extra tea or sweeteners after fermentation, the brand that came out on top was Synergy raw Kombucha. Not only was I able to spot several instances of yeast-like structures, there seemed to be bacteria across the whole field of view! It’s important to note that this is the only brand that makes some objective statement about the presence of probiotic material in it’s drinks (pictured above). So when in doubt of a kombucha’s quality, look for this label as assurance of what lies in the microcosmos of your drink! Happy Boocha Brewing and Kombucha Konsuming!