This post is the first post in a two-part series. In this post, we explain the science of garlic to create a "3 shades of garlic" tzatziki recipe. If you want to skip the science and go straight to the recipe, click here.

Why Is Garlic Spicy? Garlic Science Explained

If you have ever eaten raw garlic, you’ll know that this stuff is so spicy. Even just a little garlic can overwhelm the other flavours in any given dish and burn your mouth off in the process. Why is garlic spicy in the first place, and how can we minimise its pungency?

With the right cooking techniques and understanding, garlic can transcend its ‘spicy’ label. With the right understanding, you can fine-tune garlic’s taste and spiciness to suit whatever dish you’re trying to make.

This post delves into the science of garlic and explores various techniques for preparing it to generate diverse flavours. In part 2 of this two-part series, we’ll apply that knowledge in context with the classic garlic dish: tzatziki.

Let’s start by understanding why garlic is spicy in the first place.

Why is garlic spicy?

Garlic is an allium, which is the same plant family as onions, leeks, and chives. As alliums grow, they absorb sulfur that’s naturally present in the soil. It’s this sulfur that gives onions, garlic and other alliums that distinct aroma and spiciness.

But garlic in particular absorbs a lot more sulfur than other alliums. According to Harold McGee in “On Food and Cooking,” garlic has 100 times the concentration of sulfur compared to other alliums. This is why garlic is so much more spicy than, say, onions, leeks or chives.

But strangely, an intact raw garlic clove isn’t actually aromatic or spicy at all. It only develops these characteristics once it’s been damaged — that is, once it’s been either crushed, chopped, minced, or chewed.

You can easily test this for yourself: take a raw clove of garlic and smell it. It’ll have quite a mild smell. Next, mince the garlic clove and then smell the minced garlic. That will blow your head off. The difference is insane.

So, what’s going on here? Why does raw garlic only develop what we would call a “garlicky” taste and smell after it’s been damaged?

“This occurs due to the presence of an enzyme in garlic called allinase. When garlic’s damaged, this enzyme reacts with the sulfuric compound found in garlic called alliin.

This reaction between the allinase and the alliin then creates another sulfuric compound: allicin.

It’s this allicin compound specifically that’s responsible for garlic’s distinct aroma and spiciness. And the more that you damage garlic, the more allicin will be created. Sliced garlic is more spicy than a whole garlic clove, minced garlic is more spicy than sliced garlic, and so on.

Therefore if our goal is to remove the spiciness from garlic, then the key is to remove the allicin. As it turns out, that isn’t very hard. The key is heat.

Neither allicin nor allinase, the enzyme that creates allicin, can withstand high temperatures. When you cook garlic, it loses any allicin it contains and its ability to create new allicin.

In other words, heat up garlic and it’ll irrevocably lose its aroma and spiciness. That’s why if you microwave a bulb of garlic for 30 seconds, which some people do to make it easier to peel, it’ll have hardly any spice in it. Seriously, try it. You’ll be able to eat the whole clove easily. It’s so bizarre.

But while the microwave is a pretty simple way to kill garlic spiciness, it isn’t the best approach. There are loads of other ways to heat garlic and kill the spiciness that also create new and interesting flavours in the process.

How to caramelise garlic

You see, garlic has a large concentration of natural sugar. This high concentration of sugar means that garlic lends itself really well to caramelisation.

There’s a bunch of different ways you can caramelise garlic, but here’s one approach: slice the garlic very thinly and fry it with a little bit of butter on medium heat until it turns a tan brown colour on both sides. This creates some semi-sweet flavours that aren’t too overpowering and also removes the garlic’s harsh and spicy edge while still retaining some of that oniony aroma.

An alternative way to caramelise garlic, which will create even more sweetness, is to roast it. To do this, grab a full head of garlic, chop off the end, wrap it in tinfoil and then drown it in extra virgin olive oil. Bake the wrapped head at 180C for around 30-45 minutes, or until it looks like this:

The garlic turns very sweet, with no spiciness whatsoever, and takes on a sort of paste-like consistency. It’s great to use as a spread or to incorporate into sauces.

The “best” way to prepare garlic (hint: garlic science)

So, with all that in mind, what’s the best way to prepare garlic?

Spoiler alert: there is no “best” (or even “correct”) way to prepare garlic. It all depends on what you want to achieve.

If your goal is to remove the spiciness from garlic, the key is heat, whether it’s the microwave, the oven, or on the hob.

If you want to dull the spiciness but keep a little bit of that spice and aroma, rapidly cook the garlic in butter.

If instead you want a complex sweet taste with absolutely no spiciness, then go for roasted garlic.

Even raw garlic still has a place if used sparingly. You could use a little raw garlic, sliced or minced, as a garnish or mix it into sauces and dressings.

Or you could go for my personal favourite approach, which is using all three variants of garlic together. You could mix rapidly cooked sliced garlic and roasted garlic with your sauce or vegetables and then top that with a little bit of raw garlic for some added spiciness. And that’s exactly what I’m going to do with my tzatziki recipe.