Fermentation, oxidation or aeration
Fermentation, oxidation or aeration - confused? You won’t be!
I have been asked to further describe these three words in relation to the manufacture of black and oolong teas. I am not surprised that there is confusion and this is a mixture of historical (mis)understanding and modern pragmatism in relation to tea.
We must remember that when tea was first introduced to the west no westerner had even been to mainland China and all they knew about tea was what they were told first and second hand. Until the early 1800’s all tea came from China, through outposts of the European empires and via agents working for ‘John Company’ (otherwise known as the ‘Honorable’ East India Company) who controlled the monopoly in trade between the UK and China and the Dutch East India company controlling trade between the (now) EU countries and China.
Tea and coffee were the first non-alcoholic beverages with widespread consumption (apart from the more often than not deadly water) and most knowledge of beverage manufacture and processing came from the beer and wine (initially mead in UK) industries. Here ‘fermentation’ was and still is ;
noun the chemical breakdown of a substance by bacteria, yeasts, or other micro-organisms, especially that involved in the making of beers, wines, and spirits (oxford on-line dictionary)
This most typically is used for the breakdown of sugars to ethanol – alcohol. Surely the same underlying processes must be happening in all beverage processing? People know that tea did not have the same soporific effect on consumers but the term stuck…… For tea this is both wrong (the conversion of fresh leaf components to ‘black tea’ pigments is generally an oligomerisation or polymerisation – building small units up into larger molecular weight species – although CO2 is also given off) and misleading – no ethanol is produced during this process.
So, we have an inaccurate and – especially for religions who are forebode the consumption of alcohol – misleading term – but what are the alternatives?
How about ‘oxidation’ - noun Chemistry - the process of oxidizing or the result of being oxidized. (oxford on-line dictionary)
Well this is quite limiting. Oxidation requires both oxygen (naturally present in air) and entails the loss of electron(s) from a particular chemical species (OIL RIG – Oxidation Is Loss Reduction Is Gain – for you students of chemistry!). Electrons are the reactive species in a molecule and easily add to or depart from molecules during chemical and biochemical reactions Many chemical and biochemical reactions (those involving enzymes) in the tea process are oxidative – e.g. the conversion of catechins to theaflavins and thearubigins utilizing both oxygen and the natural enzyme ‘Polyphenol Oxidase – known to it’s friends by the catchy nick name ‘PPO’. Please note that EGCG can be known to it’s friends as PIG-3 - a rather amusing corruption of it’s official chemical name Epigallocatechin-3-gallate – go figure! However, not all reactions during the conversion of fresh leaf components to ‘black tea’ pigments are oxidations. Lipase peroxidase and glycosidase enzymes are involved amongst other things so what are we left with?
How about aeration? This charge has been led by the ISO (International Standards Organisation) – the Guru sits on the tea committee. What ISO have said is that tea manufacture is best describes by bulk or descriptive processes rather than by specifics e.g. withering (the bulk removal of water), maceration (cutting, chopping, grinding combination etc.). So aeration is the supply of air – by letting the tea sit in a suitable place or by ‘blowing’ air through a bed of tea.
You will find all three terms used in books, international standards, web sites etc. Descriptions of oolongs as ’semi-fermented’ teas, black as ‘fully oxidised’, green as non-fermented, black as ‘fully fermented etc.
Overall there is no need for concern M’am (Dragnet reference – of course) as for most part we are discussing the correct usage of the term rather than the implicit understanding. We all know that green is green and black is black with oolong sitting somewhere in the middle. But we do look to our experts to be accurate so the Guru would support the usage of the word aeration as more accurate than ether fermentation or oxidation – comments on an (e)postcard please!
KR
The Guru