In the battle between kefir and kombucha and which is healthier, it sometimes comes down to the difference between Lactic Acid Bacteria (LAB) and Acetic Acid Bacteria (AAB). Kefir has LAB (mostly) and Kombucha has AAB (mostly). Veggies are fermented by LAB. Sourdough has both LAB and AAB.
Lactic acid bacteria (LAB) and Acetic acid bacteria (AAB) both preserve foods by consuming sugars (lactose, sucrose, glucose, etc) and turning them into acids (lactic or acetic acid or another acid).
However, they are both very different in flavor and function for humans. You find LAB's in kefir (especially milk kefir) and you find AAB's in kombucha and to a lesser degree water kefir and ginger beer.
What is Lactic Acid Bacteria (LAB)?
LAB are bacteria that do well in a high acidic (low pH) environment. They create lactic acid as they consume the sugar (lactose, glucose) and that gives them the ability to naturally ferment foods safety without allowing spoilage bacteria and other pathogens to enter.
Even though there are many strains that are classified as LAB, the most common studied genus is Lactobacillus.
What are the benefits of LAB?
LAB live in the gut and if you eat them they have the potential to either temporarily help the balance or they may even take up residence within the intestines.
The most obvious benefit is that they allows you to digest lactose easier, but they also have many other health benefits that have been studied.
LAB's help regulate bowel movement. Multiple studies show that it helps alleviate constipation and possible may ease suffers of IBS.
LAB's can also help improve immune function which in turn helps prevent infections, colds and the flu. In one study, LAB's were shown to stimulate and modulate cytokine production in order to help prevent illness.
Along the same lines, there is plenty of research showing how LAB's prevent and stall the progression of cancer. Not just colon cancer, but also leukemia, breast cancer and skin cancer.
LAB's have also reportedly been shown to slow fat-cell growth and help weight loss.
Kefir is high in lactic acid bacteria, especially milk kefir. Lactic acid bacteria are also what drive veggie ferments such as sauerkraut and kimchi.
What is Acetic Acid Bacteria (AAB)?
AAB in ferments are the bacteria primarily responsible for Acetic Acid. Most people think of acetic acid as vinegar because vinegar is basically made up of acetic acid and water.
The AAB consume sugars and create acetic acid and sometimes other acids. This bacteria is the primary driver in kombucha ferments. Water kefir and ginger beer ferments are driven mostly by Lactic Acid Bacteria (LAB), but the AAB usually still take a role, albeit a lesser role.
Acetic acid bacteria need oxygen to survive, so that's why you need an open lid for kombucha ferments. But it also means that the AAB will not survive the stomach as there is not enough oxygen. Studies of human gut bacteria have not found AAB for this reason. AAB are generally not considered probiotic, at least in terms of human guts.
Lactic Acidic Bacteria are different in that they do survive in the gut and have many health giving properties as live probiotics.
So basically the benefit of acetic acid bacteria is not the bacteria itself, but the by-products of the bacteria such as acetic acid.
Acetic acid has many benefits that have been studied. Some of the biggest is that it helps control blood sugar, lowers blood pressure and inflammation.
Acetic acid is more sour and more pungent than lactic acid. Lactic acid has a smoother creamier tang to it.
Acetic acid bacteria in Water kefir and ginger beer plant
In most studies, water kefir and ginger beer plant have some measure of acetic acid bacteria. This will add to the sourness / tartness of the drink. If you want more of that sour vinegar flavor, make sure you are using an open lid as that will help the acetic acid bacteria thrive. If you are looking primary for a lactic acid bacteria ferment without acetic acid, use a closed lid or airlock to cut off the oxygen supply.
LAB's and AAB's are hard to compare as LAB's are probiotic in nature as the live bacteria interact with your own stomach bacteria. AAB's are not directly probiotic as they need oxygen to survive and will have little to no impact directly on your gut. However, they do produce healthy by-products such as acetic acid that is beneficial for health.
The amazing thing about these cultures is that they serve different purposes and have different health benefits. Milk kefir, water kefir and ginger beer are great probiotics. Kombucha is certainly a healthy ferment due to the by-products of fermentation (just like sourdough), but its not a probiotic powerhouse by itself. It's something that is rarely talked about in the industry. The yeast in kombucha may be considered probiotic by some experts, but the bacteria that survive is not really probiotic. Consuming both a lactic ferment (like kefir) as well as an acetic ferment (like kombucha) helps bring an important diversity to your diet and your gut.
Do you prefer lactic acid bacteria ferments like kefir and fermented vegetables or acetic acid bacteria ferments like kombucha?