Black Garlic: Fermentation, S-Allylcysteine and Use

Black garlic looks like a dark delicacy and tastes more of balsamic vinegar and liquorice than of raw garlic. Behind this transformation is no magic, but a slow ageing process in which the chemistry of fresh garlic shifts fundamentally. This guide explains factually how black garlic forms, what the compound S-allylcysteine is all about, and what to look for in terms of quality and use.

What is black garlic?

Black garlic is not a distinct type of garlic or a special variety, but perfectly ordinary white garlic (Allium sativum) that has been aged under controlled conditions over several weeks. The result is deep black, soft, slightly sticky cloves with a supple, elastic texture, similar to a dried date or a soft prune. The flavour is mildly sweet, slightly tangy and umami, without the sharp pungency and the typical garlic breath.

The term "fermentation" has become the standard way to describe this process, even though, strictly speaking, it isn't entirely accurate: unlike with sauerkraut or yoghurt, microorganisms play only a minor role here. Most of the transformation is driven by purely chemical reactions set off by heat and moisture. You'll find the basics on the fresh counterpart in the article Garlic and Allicin.

Black garlic has its origins in East Asian cuisine, particularly in Korea, Japan and China, where it has long been prized as a delicacy. In recent years it has also drawn attention in Europe, both in fine dining and as an ingredient in food supplements. Its appeal lies in the combination of an intense flavour and a completely different compound profile from that of the fresh bulb.

How does black garlic form? Fermentation and the Maillard reaction

To produce it, whole garlic bulbs are stored over an extended period at a constant warm temperature and high humidity. The literature usually describes temperatures in the range of roughly 60 to 80 degrees Celsius and a relative humidity of around 70 to 90 percent. Depending on the method, the process takes anywhere from a few weeks to several months. Nothing is added – no sugar, no salt, no preservatives. The cloves change purely through time, temperature and their own moisture.

The central process behind this is what's known as the Maillard reaction, the same principle that gives bread crust, roasted meat and roasted coffee their brown colour and aroma. In this reaction, reducing sugars react with amino acids and protein building blocks. Countless new compounds are formed, including dark melanoidins, which are responsible for the black colouring, along with a wide range of aroma compounds. At the same time, enzymes break down the fructans abundant in garlic – long-chain sugar compounds – which is what produces the sweetish taste.

Why does the garlic turn black at all?

So the black colour is neither mould nor spoilage, but the visible result of Maillard browning. Because this process runs slowly and at a comparatively mild temperature, it's described as a slow caramelisation inside the clove. As ageing progresses, the colour deepens from light brown through dark brown to jet black, while the texture becomes softer and the pungency decreases.

Studies on the production process describe how, during ageing, not only colour and aroma change but also measurable parameters such as moisture, acidity and the content of individual compounds. The exact results depend heavily on temperature, duration and starting material, which is why products from different manufacturers can differ in taste and compound content.

S-allylcysteine (SAC): the characteristic compound

The compound most often associated with black garlic is S-allylcysteine, or SAC for short. This is a sulphur-containing, water-soluble compound formed from the odourless precursor alliin. While fresh garlic contains only small amounts of SAC, the content rises markedly over the course of fermentation, because the ageing conditions favour the conversion.

SAC is considered a comparatively stable and readily water-soluble substance, which makes it interesting from a scientific standpoint and is why it is often used as a marker compound for the quality of black garlic. Black garlic also contains polyphenols and other compounds that form during the Maillard reaction. These are among the antioxidant-rich foods, though specific health-related claims remain a matter for the respective state of research.

From a food chemistry standpoint, the conversion of alliin to SAC is well documented. However, the exact final content varies from batch to batch, because it depends on the ageing time, the temperature control and the starting quality of the garlic. A high SAC content is therefore less a question of variety than of care taken in the production process.

Difference from fresh garlic and allicin

The biggest difference by far concerns the sulphur-containing compounds. Fresh garlic owes its pungency and intense smell to allicin, which only forms when a clove is crushed or cut and the enzyme alliinase comes into contact with alliin. Allicin is reactive and not very stable; it quickly breaks down into further sulphur compounds.

During fermentation into black garlic, this profile shifts fundamentally: the pungent, volatile, strong-smelling compounds decrease, while more stable, water-soluble substances such as SAC come to the fore. This explains why black garlic is nearly odourless and leaves no typical garlic breath. Anyone interested in the allicin side of things, or looking for an extract, will find further guidance in the guide Buying Garlic Extract: What to Look For.

It's important to understand: black garlic isn't a better or worse garlic, just a different one. Fresh garlic scores with allicin and its characteristic pungency, black garlic with stability, a mild aroma and a shifted spectrum of compounds. Which form suits you best depends on the intended use and personal taste.

Forms and SAC content: what to look for when buying

Black garlic comes in several forms. As whole bulbs or individual cloves, it's suited to the kitchen. As powder, paste, or in the form of capsules and extracts, it's offered as a food supplement, often with a standardised SAC content.

Extract and standardisation

With extracts, you'll come across figures such as a ratio of 10:1 or 15:1. This number describes how much starting material was used per unit of extract, so a 15:1 extract is highly concentrated. More informative than the ratio alone, however, is the stated actual SAC or polyphenol content, ideally lab-tested. So look for transparent labelling and a documented compound content rather than bare quantity claims.

Quality features

You can recognise good-quality goods by deep black, soft but not dried-out cloves with no off-odours. For food supplements, traceable origin, gentle processing and certificates of analysis are sensible reference points. Since black garlic consists purely of garlic, high-quality products should get by without unnecessary additives.

Use and intake

In the kitchen, black garlic is versatile: the soft cloves can be enjoyed on their own, spread on bread, or used in dressings, sauces, pasta, soups, or with meat and vegetables. Its mild, sweetish, umami aroma suits many dishes and replaces the pungency of fresh garlic with depth of flavour. Because it isn't sharp, it can also be used raw and in larger amounts without becoming overpowering. Once opened, bulbs are best kept cool, dry and well sealed so they don't dry out.

As a food supplement, follow the serving recommendation on the packaging, since dosage varies depending on concentration and SAC content. Black garlic is a food and does not replace a balanced diet. Consistent intake over a longer period is usually more sensible for food supplements than large one-off amounts, using the manufacturer's information as your guide. If you take medication, particularly blood thinners, are pregnant, or have health-related questions, discuss intake with your doctor beforehand.

Frequently asked questions (FAQ)

Is black garlic really fermented?

The term "fermentation" has become the standard usage, but it isn't entirely precise. Unlike with sauerkraut or yoghurt, microorganisms play only a small role. Most of the transformation is driven by the Maillard reaction, a purely chemical browning process caused by heat and moisture over several weeks.

What is S-allylcysteine (SAC)?

SAC is a sulphur-containing, water-soluble compound that forms from the precursor alliin, and its content increases during fermentation. SAC is considered comparatively stable and is often used as a marker for the quality of black garlic.

Does black garlic smell like garlic?

Hardly. Because the pungent, volatile sulphur compounds such as allicin decrease during ageing, black garlic is nearly odourless and leaves no typical garlic breath. Its taste is mild, sweetish and slightly tangy.

How does black garlic differ from fresh garlic?

Fresh garlic forms the pungent, reactive allicin when crushed or cut. In black garlic, by contrast, more stable, water-soluble compounds such as SAC come to the fore, while pungency, smell and texture change substantially. So these aren't two varieties, but the same garlic at different stages of ageing.

How much black garlic should you take?

As a food, there's no fixed amount – in the kitchen, taste is what decides. For capsules or extracts, follow the manufacturer's serving recommendation, since SAC content varies. If you have a pre-existing condition, take medication, or are pregnant, you should check with a doctor before use.