All you need to know about soya sauce, that essential Asian condiment

How to tell naturally fermented soya sauce from the acid hydrolysed type

Noodles flavoured with black soya sauce. PHOTO: THE STAR FILE

(THE STAR/ASIA NEWS NETWORK) - When I was young, many afternoons were spent helping my grandfather out at his little repair shop in Kuala Lumpur, just around the corner from our flat, in a district called Chow Kit. It was fascinating watching his precision using various tools darkened by usage and age to repair lamps, pumps, scales and various other household items long since rendered obsolete by electronics.

In the afternoons, my grandmother would bring his lunch in a tiffin carrier and invariably the meal will have rice with salted fish, sometimes steamed, often fried - to which my grandfather would add his preferred soya sauce before eating. It was one of his favourite dishes - and in case you are wondering, he lived till he was 93.

Perhaps I had inherited at least some of his taste genes because I can really like very salty food too, especially food flavoured with good soya sauce.

My father also used to season soft-boiled eggs with pepper and a generous splash of soya sauce, which he would eat with toast for breakfast. Even now, I sometimes still like eating that in the mornings, spread over thinly cut baguettes - and my wife likes it too, even though she has no Asian roots.

Memories of my grandfather's lunches, laced with his favourite soya sauce, trigger some saucy ruminations. PHOTO: THE STAR FILE

Despite its ubiquity, it remains true that a good soya sauce is very hard to beat as the base flavouring for many foods, including meats, fish, vegetables and Asian carbohydrate staples such as noodles and rice.

In my impecunious early years as a university student in London, one of my economies was acquiring packets of salt, pepper and soya sauces from fast-food diners to use as condiments when preparing food at home, simply because cooking at home was much cheaper than eating out.

That was when I found that those little packets are pretty unusable in a kitchen environment - the salt and pepper are full of anti-caking agents used to improve the flow of the powders and when cooked, additives such as E504 (magnesium carbonate) can really taste pretty foul.

It is the same with the little packets of soya sauces which are manufactured via chemical hydrolysis (more on this in a bit) rather than traditional fermentation. Regrettably, I did not figure all this out till much later, so for quite a while I simply thought I was a (very) lousy cook.

When working in various countries in Europe (and able to buy my own condiments), it was easy to get good soya sauces - in fact, it was so common that I never thought much about picking up a bottle of naturally brewed soya sauce from the local Asian supermarket. Usually, I get Japanese sauces, mainly because they have interesting varieties and also I like the fact that Japan is a country that takes soya sauce very seriously.

Living in the French countryside now meant that my preferred Japanese soya sauces are unavailable and invariably the available soya sauces taste different, flat and somewhat unappealing.

They also do not seem to work so well when used in trusted BBQ recipes. This got me curious about the disparity - and a little investigation confirmed that there are indeed very significant differences between various types of commercial soya sauces.


Sadly, hydrolysed soya sauce (HSS) or fermented soya sauce blended with HSS are quite often the only choice of soya sauces available in local village French shops - HSS is also generally the type packaged in those disposable packets of soya sauce you find with takeaway sushi.

As such, a lot of people will never know any other type of soya sauce, which is unfortunate as there are significant taste and aroma differences between hydrolysed, blended and purely fermented soya sauces - though one might not spot them unless they are tasted side by side. Also, in many people's minds, soya sauce is just a convenient way of introducing salt in a liquid form to food.

The good thing about HSS is that it keeps much longer than fermented soya sauce - and that is about the only major household benefit, apart from a lower cost of production as hydrolysis takes only two to three days compared to several months with fermentation.

HSS blended with fermented soya sauce also keeps longer, and probably tastes a little better than solely HSS. However, there have been issues with such blends and HSS itself in the past as you will read soon.

The actual process behind HSS is acid hydrolysis and it involves using the residue material after pressing soyabeans for oil - this material is known as defatted soyabeans.

Acid hydrolysis starts with boiling defatted soyabeans in hydrochloric acid for between eight to 20 hours in a pressure cooker to break down the proteins in the beans into amino acids.

The resulting mix is then cooled and an alkali such as sodium hydroxide or sodium carbonate added to neutralise the acidity. Then the mushy liquid is either left to settle gravitationally or pressed to extract the amino acids, which are next mixed with activated carbon particles to clarify the liquid.

Hokkien mee fried with a huge dose of black soya sauce. PHOTO: THE STAR FILE

This is followed by filtration and processing through a vacuum to further clean the liquid and remove any remaining undesirable volatile chemicals.

The result is a urine-coloured liquid called hydrolysed vegetable protein to which food colorants are added to achieve the dark colour expected of soya sauce.

Additionally, other flavourings such as salt plus a range of other ingredients (which can include items such as corn syrup, caramel, molasses, vegetable extracts, monosodium glutamate, et cetera) are now also blended in to simulate the flavour of fermented soya sauce - and it is then bottled and sold.

The harsh range of treatments to derive HSS makes it a relatively stable food compound and although HSS may also taste somewhat similar to real fermented soya sauce, there are important differences.

The use of acid hydrolysis means that practically all the original proteins in the soyabeans are converted into amino acids whereas fermented (or brewed) soya sauces leave a significant portion of the soya proteins as peptides (chains of amino acids).

Fermented soya sauce also has enzymes, esters, alcohols and other flavour compounds (eg. carbonyls) arising from the brewing process - so in reality, there should not be much similarity between HSS and brewed soya sauce.

However, most people think these two disparate products taste quite similar mainly because of the saltiness - salt is a primary taste sense and extreme saltiness tends to overpower the nuances of more subtle flavours.


It has long been acknowledged that soya sauce made via acid hydrolysis can contain chemicals such as 3-monochloropropane-1,2-diol (3-MCPD) and to a lesser extent, 1,3-dichloropropane-2 (1,3-DCP). These are part of a family of chemicals called chloropropanols which are known to be toxic to the livers of mammals.

Suggestions that 3-MCPD and 1,3-DCP can also be carcinogenic have not been wholly validated but are generally not discounted, especially as there is no doubt that these chemicals are acutely cytotoxic (cell-killing) compounds and will kill test mammals in relatively small dosages.

As such, the European Union has regulated a maximum allowable limit of 0.02mg per kg/litre for 3-MCPD for many years.

However, despite the regulatory limits, some levels of 3-MCPD and 1,3-DCP in various sauces were found to be so high that several countries, including Great Britain, Australia and New Zealand, issued a recall for several brands of soya sauce in 2001 and 2002.

These days, the quantities of such chemicals in hydrolysed soya sauces for human use are generally quite small and within the regulatory limits, especially in developed countries. This is mainly due to a constant testing regime.

The recall in 2001-2002 also applied to sauces which were blends of HSS and fermented soya sauce, and a sample processed by the Australia New Zealand Food Authority (now Food Standards Australia New Zealand) in 2001 found a staggering 630mg per kg/litre of 3-MCPD - though it appears that the recall was already initiated there when samples regularly turned up with levels of 3.5mg of 3-MCPD per kg/litre.

As fermented soya sauce contains no 3-MCPD or 1,3-DCP, any such chemicals found in blended soya sauces could only have come from the HSS component.


In Japan, traditional soya sauces are usually produced by the fermentation of soyabeans with roasted wheat mixed in. This fermentation is initiated by the addition of one or more species of fungus from the Aspergillus genus. Koji is the Japanese term used to describe the fungal cultures used to make soya sauce.

Oddly, the whole mashy mix with the added fungus is also called koji - so one might assume that Japanese soya sauce makers are rather short in their conversations.

There are some notable differences between the soya sauces made in China and Japan. A main difference is that Chinese soya sauce is made wholly from soyabeans. This translates usually to a tendency for Chinese sauces to have a denser, saltier taste while the Japanese soya would normally taste rounder, a little sweeter and have a better aroma.

If you are really intolerant to gluten (which is statistically pretty unlikely), then you should only use Chinese soya sauces.

However, all soya sauces made anywhere in the world would have been originally fermented from Aspergillus. The main species of Aspergillus used are aspergillus oryzae, aspergillus sojae and aspergillus tamari.

The first two are particularly interesting because they can use the high nitrogen content in soybeans to prodigiously produce a range of starch-digesting enzymes and importantly, also proteases (or proteolytic enzymes).

Proteases are biological catalysts which help break down the long chains of soyabean protein molecules into shorter fragments (peptides) or into the amino acids which are the basic building blocks of proteins.


The traditional way of making soya sauce starts with preparing the mash mix version of koji. This involves soaking soyabeans in water until the beans contain around 60 per cent moisture - then they are cooked in a pressure cooker for around 45 minutes.

At this point, if one is in Japan, wheat already pre-roasted at 150 deg C would be cracked into several pieces (and some residual flour) and this cracked wheat and flour is then added to the cooked soyabeans.

Left: A traditional soya sauce maker in Malaysia slow-fermenting the cured soya beans in order to make soya sauce. Right: Soya beans fermenting, waiting to be turned into soya sauce. PHOTOS: THE STAR FILE

The quantity of wheat varies depending on the type of soya sauce required. The spores of aspergillus oryzae or aspergillus sojae is then mixed into the soyabean (and wheat) mix and crushed together.

The resultant mash is then spread onto wooden trays to a depth of 3 to 5cm.

After laying out on wooden trays, the koji is then left to ferment in a warm room at 25 to 28 deg C for 72 hours, resulting in a yellow-greenish gunk due to the growth of the Aspergillus mould.

This gunk needs to be constantly stirred, to dissipate any irregular heat spots in the mash arising during the fermentation process.

This fermentation stage is very important because it is when the Aspergillus mould starts generating the various enzymes which will eventually digest the proteins and carbohydrates in soybeans - this is a fascinating story in its own right which will be explained later.


As a result of the enzymes created by the Aspergillus mould, the starches and proteins in the soyabeans are on the way to be broken down into sugars and peptides. The mix is now ready for the introduction of other bacterium and yeasts for the next stage, which is called brine fermentation.

This is when brine at 20g salt (sodium chloride) per 100ml is added to the fermented koji. The use of brine is primarily to stop the growth of unwanted organisms as the bacterium used (pediococcus halophilus) and the yeasts (zygosaccharomyces rouxii and candida) have the remarkable ability to flourish in a salt solution of 20 per cent.

The first stage of brine fermentation involves mixing the fermented koji with cool brine and pediococcus halophilus to create a watery sludge (called moromi in Japan).

After the treatment with Aspergillus, this watery mix should be very mildly acidic, with a pH of around 6.5.

This mixture is then transferred to large steel tanks with internal temperature control coils to continue fermentation at a reduced temperature of 15°C for 30 days or until the pH drops from the original 6.5 to 5.0. The pH falls (or acidity increases) because pediococcus halophilus is fermenting the sugars into lactic acid.

During the entire brine fermentation process, the Aspergillus mould is also salt-tolerant and continues to produce enzymes and breaking down soy starches and proteins in the moromi into simple sugars, peptides and amino acids.

This causes an amino acid-glycosidic reaction which results in the production of dark reddish-brown compounds called melanoidins due to the Maillard reaction.

If you are curious about the Maillard reaction, you can review an earlier article on it, here.

The second stage of brine fermentation involves the addition of the yeasts zygosaccharomyces rouxii and candida to the tanks and then slowly increasing the temperature of the mixture to 28 deg C until alcoholic fermentation begins.

This means the yeasts are converting sugars into ethanol. This alcoholic fermentation stage lasts around two to four months during which more of the brine bacteria and yeasts may be added to maintain the fermentation process.

The combination of lactic acid, ethanol, melanoidins, simple sugars, peptides, amino acids and other fermentation by-products is what gives fermented soya sauce its unique flavours, colour, aromas and other characteristics.

After a few months, the fermented soya mixture is now ready for the final processes of pressing, filtration and bottling as soya sauce.

Most modern soya sauces will also undergo pasteurisation at around 70 to 80 deg C for a few minutes before bottling - but I sometimes prefer to use unpasteurised soya sauce (the reasons will be explained later).

The fermented watery mixture is now transferred from the brine fermentation tanks into vertical presses which will separate the sauce from the residue. The sauce is then filtered and clarified further by sedimentation or centrifugation as necessary.

Before bottling, quality control checks would be done at the factory to assess not just the sensory attributes of the soy sauce (taste and aroma), but also the pH, amino acid content, saltiness, colour, microbial contamination levels, ethanol content and so on.

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