Fermenting: how do we use bacteria and fungi in food?

30 Aug

Cheese and wine... what a treat (courtesy of Microsoft Clip Art)

Warning:The reading of this blog may make you to break out a nice bottle of wine and a cheese board and enjoy it in the company of some good friends (or just have it by yourself). You have been warned feel free to continue.

Is there anything better than wine and cheese (well except for maybe chocolate)? It seems that most of our favourite foods and beverages are produced through fermentation. But what is it about fermentation that makes it taste so good?

Lets get technical for just a sec (and then we can go back to discussing food). Fermentation (the process of fermenting something) is basically taking a sugar (carbohydrate) and turning it into an acid or alcohol. This is done using fungus (yeast) or bacteria (but good ones not the ones that make you sick).

Fermentation using yeast makes some of our favourite products including bread and alcohol. Yes that’s right, yeast is placed into sugar sources (like grapes, barley, apples ect) to make different types of alcohol. Yeast is also used to make bread, another fabulous food. The most ancient use of fermentation was, you guessed it, to make alcohol, dating back to Neolithic times (which is really old). How is it that fruit, vegetables and grains mixed with a small microbe produce an amazing treat? Well there are many different ways, each providing a unique flavour but I’ll explain the basics. After the sugar source is collected it is made into a mash. The mash is then mixed with hot water. This is transferred to a fermentation vessel and yeast is added. Yeast, like human cells, works best between 30-37°C, hence the hot water. Fermentation begins, the yeast metabolise (“eat”) the sugar, the by products are alcohol and carbon dioxide gas. After the yeast does its thing, the alcohol is filtered out and prepared for human consumption.

Bread fermentation follows the same principal, activated yeast (warmed up) is added to the dough. The dough is left to rise (which is when fermentation takes place). The carbon dioxide gives bread is fluffy, light texture and the alcohol provides the taste (no you can’t get drunk on bread, the alcohol evaporates during the baking process).

Enough about yeast fermentation, now it’s time to devel into the dairy arena. That’s right some of our favourite dairy products are made by fermentation. Yoghurt, sour cream and cheese are both made by fermenting milk using special bacteria that produce lactic acid. Basically, milk is collected from either cows or goats, and processed (so that the liquid bit goes for drinking and the solid parts are used for other products) and then heated to remove natural microbes that are in the milk (some might be dangerous). After the milk is processed bacterial cultures are added to the warm milk and left to ferment (once again fermentation happens better in heat). The bacteria metabolise the sugar (lactose) found in milk into glucose (another sugar) and then into lactic acid and acetaldehyde (a chemical that gives the distinctive tangy taste). Yes the dairy product we enjoy so much are basically flavoured, curdled, fermented milk. After this a whole bunch of other manufacturing stuff happens to add flavours, age cheese and make these products delicious. Blue cheese (which personally I don’t particularly like) is of special interest to this blog. Blue cheese goes through this process and then a fungus (the mould Penicillium) is added to the cheese. This mould is what provides the distinctive blue-green or blue-grey lines in the cheese.

Other fabulous foods made by fermentation includes chocolate, coffee, tea, soy sauce and vinegar. It seems all the best foods are fermented. So while some bacteria and funguscan be very bad for us, they are also our friends. Although I wouldn’t suggest eating the fermenting fruit or mould food products in your fridges or cupboards. Next time your enjoying a glass of wine with a cheese board, a beer and pie or a yoghurt with cereal remember that it was fungus and bacteria that gave those products the wonderful flavour you are enjoying.


Posted by on 30/08/2011 in Uncategorized


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2 responses to “Fermenting: how do we use bacteria and fungi in food?

  1. Tomoko

    29/09/2011 at 19:03

    Fermented food are mostly food for health. For example, Yogult are very good for health. Talking about Japan, there is “Natto” which is fermented soy beans which is very sticky but very healthy. Many people eat it in the morning and it is officially proven as a healthy food!

  2. collegekitchenscientist

    30/09/2011 at 11:36

    I don’t know if all fermented food is good for your health, maybe in small doses but the jury is still out on the benefits of alcohol.


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