Fermented foods - tasty, safe and good for you.

Recently, one of my regular readers watched a BBC television programme on 

"Which foods can improve your gut bacteria?" narrated by Dr. Michael Mosley.  She wrote and asked me  to comment on the safety of such foods, how they should be stored, plus potential risks of manufacturing them at home.

Traditional, naturally fermented foods have been around for hundreds, if not thousands, of years.  These days, we tend to relate the term "Fermented food" to sauerkraut, kimchi, tempeh, or perhaps yoghurt and cheese.  However, the Egyptians knew about wine production 5,000 years ago (though they didn't know that yeasts were involved).

Fermentation is a natural process, carried out by bacteria, yeasts and occasionally moulds, that actually preserves raw foods, often by production of acid or alcohol, which prevent spoilage.  Of course, the preserved food sometimes bears little resemblance to the original.  We enjoy these foods because the fermentation changes the flavour and texture of the raw material, often increasing the complexity.

We now know that our gut microflora, now called the gut biome, can be influenced for the better by consumption of some fermented foods.  The microorganisms that carry out the fermentation can sometimes pass through the very acid conditions of the stomach and may be able to colonise the gut wall, perhaps displacing undesirable bacteria, though some just pass through, having a transitory effect on the gut biome.  They can help with traveller's diarrhoea or lactose intolerance.

Dr. Mosley and his team investigated the claims for such benefits by setting up three groups to consume various fermented products for four weeks and looked for changes in their gut bacteria.  You can read about it in the link above.

The team also tested the products to determine the range of bacteria in them.  Home-made fermented foods tended to contain a diverse range of bacteria, while commercial products, which may have been pasteurised, often contained very few.  Thus the flavours and textures would be similar, but the potential health benefits of the microbial populations had been removed.

Over many years of teaching food microbiology, I made sauerkraut with my students.  It's an easy fermentation to carry out, requiring only finely shredded cabbage and about 2 - 2.5% salt packed in a suitable container.  Air must be excluded to prevent the growth of moulds on the surface of the kraut. We followed the fermentation daily, counting and identifying the bacteria taking part, and measuring the titratable acidity and pH.  

We always found a succession of bacteria.  The undesirables, like Escherichia coli and other coliforms disappeared within the first couple of days as lactic acid bacteria produced lactic acid and reduced the pH.  Leuconostoc  species, found on the inside leaves of the cabbage, would begin the acid production, giving way to Lactobacillu plantarum and eventually L. brevis.  The final pH of the sauerkraut is around 3, which is plenty low enough to prevent the growth of pathogens.

The kraut can be stored in the refrigerator for a short time, but must be protected from oxygen to prevent spoilage.  If you would like to make some at home, download the original recipe, written by Carl S. Pederson in 1939.  He studied the fermentation extensively over many years.  There are many other, more recent recipes available on-line and much has been published in the scientific literature on the microbiological changes that occur during fermentation.  You can also find many recipes for kimchi on-line.

Are home-made fermented vegetables safe to consume?  Yes, provided that the fermentation has produced sufficient acid to lower the pH to around 3 to 3.5, which will prevent the growth of pathogenic bacteria.  The finished product must not be allowed to go mouldy, since moulds can metabolise the acid and raise the pH to levels at which pathogens could grow.  My son, who is an electronics engineer, has successfully made sauerkraut and kimchi at home.  You don't need to be a microbiologist or food technologist to make safe, tasty fermented foods!

Cidre with that extra fizz could be a nasty surprise

The UK Standards Agency announced on the 18th September that InBev was recalling three batch codes of Stella Artois Cidre in bottles.  Fruit juices and alcoholic beverages make few appearances in lists of hazardous foods and drinks, and this is the first time they feature in Safe Food.

The problem with these batches is yeast.  Yeast is used in bread making, beer fermentation and, of course, Vegemite, the breakfast spread many New Zealanders were brought up on.  So why is yeast dangerous?

Yeasts convert sugar to alcohol and carbon dioxide.  They put the fizz in beers and sparkling wines.  If this occurs in a controlled fermentation process, there is no problem.  However, if yeasts get into finished products containing sugar, such as bottled fruit juices or alcoholic beverages with residual sugar (not fermented to "dryness"), they can produce carbon dioxide in the bottle.  The cells can generate pressures up to 10 atmospheres - sufficient to burst the bottle.

The recall notice says:

• handle the bottles carefully, wearing gloves and protective eyewear, to determine if the product is from the affected batch
• on an individual bottle, the batch code is printed on the bottle’s neck
• on a 12-pack the batch code can be located on the long side of the pack, to the right of the barcode

If you do have a product from an affected batch, please call InBev as soon as possible on 0800 0731736 between 8am and 8pm. Do not consume or handle the product further.



I once saw a similar recall notice that effectively invited anyone having the affected product not to touch it, but to call the bomb squad!

This may sound a bit melodramatic, but think about this:
One of my winemaking colleagues wanted to produce sparkling wine from a batch of still wine.  He calculated the amount of carbon dioxide to dissolve in the wine and added this to the bottles as small pellets of carbon dioxide ice.  He put corks in the bottles and wired them on and then stored the bottles in a cupboard.

A few hours later, there was a tremendous bang from the cupboard.  He found only the necks and bases of the bottles; the rest was fragments, many of them embedded in the wooden walls of the cupboard.  We could only assume that the carbon dioxide had been slow to dissolve in the wine and the pressure had built up too fast.  This could have been very nasty had he been holding a bottle at the time.

As they say in the extreme sports programmes, "Don't try this at home".

Will spoiled food make you sick?

I recently received a message from Jo, asking me to comment on this subject.  Jo actually raised a lot of questions and, of course, the answers are not simple.

First question:  If the food smells off, tastes bad, has a poor colour etc. is that a good indicator it will make you sick?

Humans have been on the Earth for a long time and one of the reasons they have survived for so long is that they have evolved self preservation mechanisms.  If the food smells off or doesn't look right, there is a chance that it is poisonous in some way and we tend to avoid it.  Sometimes I wonder what the first people to taste durian or blue cheese thought they were doing!  So, clearly, the answer has to be a qualified "Yes, it might make you sick, but some sort of tribal wisdom suggests that a few foods can look and smell awful but still be OK to eat".

Jo then went on to say that she thought that the food was unlikely to make you sick, as the changes were caused by spoilage bacteria and enzymatic reactions, which are not the same as pathogenic bacteria, which she thought do not alter the food in the same way.

This is where it gets complicated.  Spoilage bacteria do cause some changes, which, by definition, make the food unacceptable to most people.  Other bacteria, such as Salmonella, may grow alongside the spoilage bacteria.  When the food is eaten, the salmonellae  set up an infection in the gut and produce the familiar food poisoning symptoms.

Second question: Is it true that pathogenic bacteria don't alter the food?  Again, it depends on the bacteria.  Generally, clostridia alter the food a lot, producing many smelly compounds and gas.  This would put most people off eating the food, so they would be safe.  But some Clostridium botulinum strains are non-proteolytic.  That is, they don't break down proteins and they don't produce the foul smells that the proteolytic strains make.  So you could find improperly processed canned foods that appear quite normal, but could kill you.

Jo's third question was perhaps the most fascinating: she was most interested in how the food could potentially have both types of bacteria on it near to the time it was made and correctly identified contamination of the food as the cause, possibly by cross-contamination from some source.  A good example would be a careless food handler.

At this point, the food could cause food poisoning if consumed - Salmonella transferred from raw meat to a cream pastry would be a good example here.

Jo went on "However as time goes on and assuming the food gives them all the things they both need to grow, is it as simple as the pathogens might be around for a short time until the spoilage guys, who being better competitors for resources, take over; so by the time the food
is showing signs of being spoiled, the pathogens have been killed off?"

That's a really insightful comment.  Many fermented foods are actually safe because of this pattern.  Take raw cabbage and make sauerkraut:  we shred the cabbage and add about 2.5% salt to it and then press it into a container and seal it.  The salt draws out the tissue fluids from the shredded leaves and bacteria naturally on the leaves begin to produce lactic acid.  If we sample on the first day, we can find all sorts of bacteria, including Escherichia coli and possibly Salmonella.  However, as more acid is produced, the pH falls and the potential pathogens die off.  Finished sauerkraut has a pH around 3.1 to 3.7 and is perfectly safe to eat, though there has been a lot of bacterial growth in it.

So, to return to Jo's original question, "Is spoiled food potentially safe to eat, even though it looks and tastes awful?"    Sorry Jo, I can't answer that.   But if it tastes awful, why would you want to eat it?

One last point:  there is an anecdote that a lady opened a can of peas and thought that they looked a bit different.  She tasted one and cooked the rest.  She died of botulism.  Ironically, if she had cooked them and then tasted one, she would have lived, as the botulin toxin is heat labile.  I don't remember where I read this - it was somewhere around 1980, but it's a good example with which to finish this article.