KOMBUCHA IN ALUMINIUM CANS TIME BOMB IS TICKING. INDUSTRY MUST ACT
‘LACTIC AND ACETIC ACIDS IN SOUR BEER PROMOTE CORROSION DURING ALUMINIUM BEVERAGE CAN STORAGE’ is the alarming heading of a landmark study into the corrosive effect of acidically active soda beer in aluminium cans…
The study, published in October 2024, is funded by the US Brewers Association and the USDA National Institute of Food and Agriculture as “a step towards evidence-based determination of factors causing corrosion in other canned beverages with high levels of volatile organic acids”, such as kombucha.
Its findings are consistent with the following:
Active organic acids in plastic and epoxy resin-lined aluminium cans are far more corrosive than traditional, ultra-processed sodas and colas.
The dominant acid in kombucha, acetic acid, is more corrosive than lactic acid, the main acid found in sour beer.
Heat-treating kombucha in sealed cans or storing ambiently vastly increases the potential for aluminium contamination.
Active acids increase corrosion
Its findings will concern regular consumers of commercially produced drinks containing active organic acids packed in aluminium cans regardless of the type of inner liner – acrylic, epoxy resins or porous polymer plastic pouches – which are supposed to provide a complete barrier between the aluminium and the can’s contents.
A similar 2023 study into the corrosive effect of inert, low pH/acidic drinks like Green Coke and Red Bull found relatively small amounts of aluminium in test samples across all liner types, varying in volume depending on factors such as the number of cans consumed daily, length of time in can/sell by date and storage temperature.
In summing up, the new study — the first to be carried out on sour beer, which is similar in active microbial acidity and pH to kombucha — concluded that all can liner types failed to prevent varying amounts of aluminium corrosion and leakage, and significantly more than found in Green Cola and Red Bull in the 2023 study...
More corrosive than Coca Cola
Phosphoric acid in colas and sodas is stronger than the acetic and lactic acids found in sour beer and kombucha. It gives these popular drinks their tart flavour and sharpness while also preventing bacteria and mould growth. However, sour beer, kombucha and variants thereof contain potentially billions of active organic acid molecules per can that increase aluminium corrosion via all types of can linings compared to standard canned drinks. The level of corrosion is correlated with the concentrations of total (titratable) acidity present. pH alone was not a good predictor of can corrosion, further suggesting that organic acids (and not free protons) are involved in the corrosion of lined beverage cans.
The lower the pH and higher the total acidity (a complex correlation) in a test sample, the higher the level of corrosion was found to be, eventually placing outward pressure on the can due to active microorganisms producing CO2/gas, leading to signs of swelling – including buckling at the top and base of the can – and, potentially, explosions.
Aluminium corrosion increased in all the sour beers tested in a time-dependent manner, with measurable increases in dissolved aluminium occurring in all between six to 24 weeks. After week 24, sour beer in the acrylic-lined cans made by one manufacturer had twice the amount of leeched aluminium compared to the acrylic-lined cans made by another manufacturer and the epoxy-coated cans, which performed similarly to each other.
W.H.O. advice on aluminium intake
Aluminium concentrations in one 48-week-old can were found to be as high as 58mg/L – 100-fold greater than in concentrations found in non-sour beers and far exceeding the World Health Organization (W.H.O.) recommended total weekly intake of <2mg of aluminium per kg body weight, or <150mg for a 75kg person. [Note: 1000mg = approximately 1ml. This particular batch of sour beer was not commercially released due to its high acetic acid content].
The next highest level of aluminium was 3mg per standard-size 355ml can, around a third to almost a half the amount typically ingested via an average daily diet. To reach the total weekly intake of aluminium at that level as defined by the WHO, a 75kg person would need to consume at least 7 x 355ml cans a day.
When also factoring in aluminium intake from non-food sources such as kitchen utensils, tin foil, antacids, beer kegs, antiperspirants, toothpastes, beauty products and vaccinations as well as from the environment, the study infers that consuming several cans of sour beer daily can make a significant contribution to a person quickly reaching the W.H.O.-recommended level.
Acetic acid and kombucha
However, where canned kombucha is concerned, the potential for over-consuming aluminium is potentially significantly higher than sour beer. Excessive acetic acid is usually considered a flaw in sour beers, while it’s a defining characteristic of kombucha. Conversely, compared to standard beers, lactic acid is dominant in sour beers to provide the sour taste, with up to 7.0g/L compared to around only 0.5g/L in kombucha.
And while sour beer’s relatively high titratable acidity concentrations of around 5g/L are similar to traditional kombucha, kombucha's pH is slightly lower likely due to the dominant acetic acid present which gives kombucha it's bite and sharpness; 1.0 to 3.0g/L of acetic acid in kombucha compared to 0.3 to 1.4g/L found in sour beer.
Therefore, the considerably higher concentration of acetic acid in kombucha correlates to far higher levels of aluminium leeching than the already alarming amounts this study found in sour beers!
K.B.I. responsibility/duty of care
An increasing number of kombucha brands have been packaged in cans for almost a decade. Yet none have been publicly or officially tested for consumer safety. Despite a lack of scientific evidence about aluminium toxicity and the body’s ability to flush out excess aluminium, the degradation in can linings found in recent studies raises real concerns and questions for the kombucha industry.
It is now incumbent, therefore, on the Kombucha Brewers (K.B.I.) trade association to pursue and assess the levels of aluminium corrosion and product contamination across the broad range of traditional kombucha and variant kombucha drinks its members produce to ensure they fall within levels that the body can manage safely.
Consumers deserve to know which level of daily consumption of traditional kombucha and its variants may cumulatively impact bone development and brain function. Medical science now points to aluminium poisoning as a key driver of Alzheimer’s, Parkinson’s and multiple sclerosis, among other progressive neurological disorders.
Notwithstanding there is still no safety standard to address explosions of kombucha packed in sealed, airtight cans and tightly sealed glass bottles. It will only take a couple more incidents of injuries sustained from ‘kombucha bombs’ to go viral on TikTok for the global tide to turn against commercial kombucha…
Recommendations for brewers
K.B.I. needs to act on those findings and recommend a course of action to both members and non-members globally to ensure consumers’ well-being is prioritised above all else. Recommendations such as:
Reducing product shelf-life.
Recommending a daily can limit for consumption on every can.
Ensuring chilled storage throughout the distribution chain.
Sourcing manufacturers of more durable and less corrosive inner liner types.
Ending the practise of pasteurising inside sealed cans (heat considerably exacerbates aluminium leeching).
Or, mitigate all such issues and other potential pitfalls – including contamination by microplastics and chemical residues from the liners, some of which still contain the ‘hormone disruptor’ BPA – by switching to the good old glass bottle with a pressure release cap, as used by GO Kombucha ever since we first paved the way for commercially produced kombucha in the UK in 2003.
Aside from being made from just three natural ingredients – soda ash, limestone and sand – glass is the natural environment for storing kombucha, preserving as it does the quality and flavour of the drink.
Industry expert Gary Spedding Ph.D warns: “More due diligence is needed!”
GO Kombucha approached the US Brewers Association and K.B.I. for comment, but neither responded to our call to action. So we approached Gary Spedding Ph.D, a leading US brewing and distilling analytical chemist and biochemist who has participated in several kombucha test protocol collaboratives and conversations, and this is what he had to say:
“IN MY OPINION kombucha has no place in cans whatsoever. Acidity at such levels is just asking for a disaster. The simple fact of the matter is these types of beverages have not been subjected to the necessary testing in cans.
“Kombucha producers need education in what they are doing. Just as do craft brewers turning to commercial production. No one is even doing simple force testing of products nor getting them tested for a number of critical quality control points.
“I have suggested to the industry, including K.B.I., for over a decade and a half now, that product warning labels need to make it clear that this product can referment/continue fermenting and promote gas build-up to explosive levels.
“Acidity and pH, while related, are not the same thing in terms of the chemistry that can cause corrosion. Other metal ions and chlorides are also a concern – tea itself can be corrosive! More due diligence on testing, storage/distribution and home storage conditions for such products is needed in the industry on this very explosive topic.
“I have just been helping a fellow injured in a keg explosion ten years ago, which was filled with sour beer and housed unrefrigerated in a warehouse – a potential issue with kombucha no matter how packaged.
“No compensation so far from the keg company, and he has no money left to his name. He was charged $150,000 for a report by a so-called expert who did not address the corrosivity issues, or examine the remains, or perform a test set up.
“Any accident or harm to a customer’s health could financially ruin and finish the business of a kombucha producer. And in the US at least, potentially some jail time.”