The Science of Cooking With Garlic
Understanding allicin — the sulfur compound behind garlic’s unique taste and smell — just may help you be a better cook.
By Ted Jordan Meredith
Pressing garlic releases the enzyme alliinase, forming the sulfur compound allicin, which is responsible for garlic’s complex flavor.
There’s a lot to know about raw garlic in its various forms. In The Complete Book of Garlic (Timber Press, 2008), Ted Jordan Meredith tackles what he calls the next gourmet frontier, giving detailed information for cooks, chefs and natural health enthusiasts. The Complete Book of Garlic gives guides to planting and growing garlic for the best results in the kitchen and in home remedies. In this excerpt from the “Cuisine” chapter, Meredith explains how garlic gets its taste.
Garlic’s composition, chemistry and enzymatic interactions determine how different preparation methods affect its taste and thus the taste of the culinary preparations that include it. These same preparation methods also define and determine the therapeutic effects of garlic. Understanding this nexus helps us better understand our culinary choices. Considerations of taste and health both help shape the methods we may choose to apply.
Allicin, Alliin and Alliinase
The chemistry of garlic is complex and dynamic but let us briefly touch upon three fundamental constituents and the role they play in taste and therapeutic effect. The sulfur compound allicin and its derivatives are substantially responsible for garlic’s pungently complex flavor and aroma as well as for a substantial amount of its therapeutic benefit, yet a whole clove of garlic contains no allicin and has essentially no aroma. How can this be?
Allicin is only created when the enzyme alliinase interacts with the sulfur compound alliin. When alliinase and alliin are brought together, the creation of allicin occurs with great rapidity. Alliinase and alliin are held in isolation in separate cells of the garlic clove and are only brought together when the cell walls are compromised, such as occurs with crushing, chopping, slicing, and biting.
Try this. Smell a whole healthy clove of garlic, then smash it with the flat of a knife and smell again. The aroma instantly goes from nothing to intensely pungent. The creation of allicin happens that quickly.
Garlic Preparation Methods
Now that we have a basic understanding of garlic’s taste chemistry, we can begin to see how the way garlic is prepared greatly affects its character. Bringing alliinase in contact with alliin not only produces allicin but also initiates a cascade of transformations that result in the creation of many more sulfur compounds that contribute to taste and therapeutic benefit. If garlic is cooked whole, no allicin is produced, and the flavor is not only milder but also simpler and very much different from garlic that has been chopped or crushed prior to cooking.
When I first started growing garlic and began to acquire some of the less common cultivars, I decided to have a garlic taste test. I sautéed whole cloves of a number of cultivars and carefully kept them identified and separate. I was disappointed in the bland flavor of each one and found very little difference between them. I did not realize at the time that their distinctive characteristics and flavors could only be realized if the cloves were chopped or crushed prior to cooking. Garlic that is baked or sautéed as whole cloves has a legitimate culinary role, but one should not expect the same flavors, complexity, or intensity of garlic that has been crushed or chopped.
Heat destroys allicin, but chopping or crushing garlic prior to heating allows the creation of numerous additional sulfur compounds, contributing to flavor as well as likely additional therapeutic benefit. As we will discuss in more detail in chapter 4, allicin and its secondary constituents are substantially responsible for garlic’s therapeutic effects. If therapeutic benefit is the primary goal, garlic should be chopped or crushed and consumed raw. However, raw garlic need not be consumed in great quantities for therapeutic benefit: a clove per day is more than sufficient.
Garlic that has been chopped and sautéed still has significant therapeutic benefits, though not the full range of benefits as raw garlic. In any case, one should not feel constrained to eat only raw garlic for health purposes. For some culinary preparations raw garlic is the perfect match, while cooked garlic is preferable for other preparations
Crushed Raw Garlic
Most garlic aficionados, in the course of exploring their passion and affliction, will take a bite out of a clove of garlic or perhaps eat a whole clove at a time, being sure to chew it well so that the alliinase is thoroughly exposed to alliin to create allicin—and the cascade of related volatile sulfur compounds that follow. Eating raw garlic in this matter is certainly a bracing experience, particularly for the uninitiated. The intensity and heat can be startling and unpleasant. Some cultivars, such as many Silverskins, can be stingingly hot. Others, such as some Rocamboles, seem almost sweet in comparison—but only in comparison. Eating raw garlic by itself is usually not a culinary preference. However, raw garlic in combination with other food is an excellent choice in some preparations, adding a fragrant, vivid brightness not present in cooked garlic.
Although for raw consumption garlic can be chopped or minced, it is usually preferable to crush it. Crushing more fully combines alliinase with alliin to produce the maximum amount of allicin and other compounds. It also allows the garlic to be more thoroughly and evenly distributed with other food.
You can crush garlic by placing a peeled clove under the blade of a chef ’s knife, mashing it flat with a whack on the blade with the palm of your hand, and then mincing with the edge of the knife. This method works well, though I prefer a quality garlic press for the task if one is available. Some chefs crush the unpeeled clove and dispose of the skin afterward. I find this a bit messy and wasteful, but it is certainly an option.
This method works better on some cultivars than others. If salt is part of the preparation it can be an ally in further crushing the garlic. Put the crushed garlic in a small bowl. Add salt and use the back of a spoon to crush the garlic by using the salt as miniature grinding particles. This method extracts the juices as well and quickly produces a garlic slurry.
When we incorporate crushed raw garlic into our cuisine we need to keep a few principles in mind. Acid and heat inactivate the enzyme alliinase, and heat destroys allicin. When garlic is crushed, alliinase interacts with alliin to form allicin. At room temperature the process is complete within 10 seconds. Although the process is extraordinarily rapid, it is not instantaneous.
If we are preparing a salad dressing for fresh greens, we should not press garlic directly into vinegar or citrus juice. Although much of the transformation of alliin into allicin would likely occur, it is better to ensure the transformation is complete before the alliinase is inactivated by the acid. Crush the garlic into a small bowl, then add the vinegar or citrus some 10 seconds or more later. If we are adding salt, pepper, or other herbs or spices, this would be a good point to add them, and if we desire, further crush the mixture into a slurry with the back of a spoon. Next, add the vinegar or citrus, mix together, and then add and mix the salad oil.
The same principles apply to other cuisines. For example, if we are making a classic Vietnamese or Thai dipping sauce or “salad dressing” with lime juice, nampla (fish sauce), garlic, and sugar, we should crush the garlic first and wait at least 10 seconds before adding the lime juice.
Continental cuisine includes raw garlic in various preparations, such as tapenade, persillade, and gremolata. For the most part, however, classic Continental cuisine does not include raw garlic in sauces. When garlic is included in sauces it is typically minced and then sautéed until soft or straw-colored prior to adding liquids and other ingredients. This is a classic culinary approach and a basis for wonderful cuisine—but are there other possibilities?
The flavors of crushed raw garlic are hotter, more aggressive, more vivid, and more fragrant than garlic that has been chopped and sautéed. The allicin in crushed raw garlic is destroyed by heat, so putting crushed raw garlic into a bubbling hot sauce essentially cooks it and destroys the aromatics associated with raw garlic regardless of any culinary merit.
More frequently incorporating crushed raw garlic into our cuisine is certainly desirable from a therapeutic standpoint. From a purely culinary standpoint, could an expanded role for crushed raw garlic have merit as well?
In The America’s Test Kitchen Cookbook put out by Cook’s Illustrated magazine (2001), the editors explore different approaches to the classic dish spaghetti allacarbonara:
At first we sautéed a few minced cloves in a little olive oil before adding it to the sauce, but this sautéed garlic lacked the fortitude to counterbalance the heavy weight of the eggs and cheese. Adding raw garlic to the mixture was just the trick. A brief exposure to the heat of the pasta allowed the garlic flavor to bloom and gave the dish a pleasing bite.
So what is happening here? The crushed raw garlic is warmed by the dish but not heated to the point of destroying the allicin and other aromatic volatiles. It is successfully incorporated into the sauce, where it plays a counterbalancing role to the other ingredients. In good cooking, and indeed in all great cuisines, ingredients are added to balance and counterbalance. Here the eggs and cheese give the dish a wonderful richness, but without the aromatic bloom of the raw garlic the dish would be a bit heavy and dull.
This approach suggests a method for expanding the role of crushed raw garlic in our cuisine. Adding crushed raw garlic to a sauce or dish when it is warm but not hot preserves the allicin and other volatiles, retains their therapeutic benefits, and adds another flavor to our culinary toolset.
There are countless variations on this theme, but a basic cooking method in Continental cuisine calls for sautéing a meat; removing it from the pan; adding onions, garlic, or shallots; sautéing briefly; adding water, wine, or stock; scraping and stirring the fond from the pan into the stock; reducing and concentrating the mixture to create a sauce, sometimes including starch for thickening; and as the mixture is cooling, adding butter or aromatic olive oil for flavor and enrichment. After this last step is completed, and after the sauce has cooled from hot to warm, we can add another step if we so desire: we can fold in crushed raw garlic just prior to serving.
I sometimes employ sautéed garlic and other alliums for the rich foundation they contribute, and crushed raw garlic for the finish. Of course, this does not mean that one should always add crushed raw garlic. Sometimes a dish is best without it, and sometimes one’s mood may call for one preparation over another. Just as one is not confined to only one herb or one spice, crushed raw garlic simply adds to our culinary choices.
As a finishing element, crushed raw garlic works well with red meats and rich sauces. It also works well with lighter meats and fish, usually augmented with lemon or other acids to lighten and brighten the effect. Crushed raw garlic can be added as a finishing element to other dishes as well. It may be sacrilege, but adding crushed raw garlic to such classics as, for example, beef bourguignonne or Viennese goulash just prior to serving offers another culinary possibility. The dishes become something a bit different—but good.
An expanded role for crushed raw garlic is not confined to Continental cuisine but applies quite broadly. For example, crushed raw garlic works well with Thai curries. The flavors meld well. The additional heat is barely noticed and is counterbalanced by the dish’s underlying sweetness, which is already employed to counterbalance the heat of the chilies.
In different ways sweetness and acidity help counterbalance the aggressive elements of raw garlic and emphasize its richness and fragrance. Cooked vegetables or greens, still warm, can be tossed with a mixture of crushed garlic, salt, balsamic vinegar, and olive oil—similar to a dressing for fresh greens but with less vinegar and more oil. Experiment and explore.
Crushed raw garlic can be quite hot and aggressive. Consequently for raw garlic I usually prefer cultivars with a richer, sweeter, less hot profile, such as a Rocambole or Creole, or perhaps a Purple Stripe. I generally avoid hotter and more aggressively sulfurous cultivars such as Porcelains and Silverskins. For a dish such as a Thai curry, which again is already geared to counterbalance heat, the differences are less important. Other dishes are much more sensitive. For salad greens, for example, I always choose a sweeter garlic.
I am not advocating that we abandon the traditional methods used in classic cuisine or avoid cooked garlic in favor of raw garlic. Crushed raw garlic is simply an alternative that can add variety to our cuisine. Raw garlic has played a somewhat limited role in cuisine. Its therapeutic benefits are an incentive to explore an expanded role, and as we have seen, there is culinary merit to this pursuit.
Sautéed Garlic
Chopping or crushing garlic and then cooking it in oil is a basic preparation method throughout the world. The chopping or crushing generates the volatile, aromatic flavor, which is then tamed and deepened by the cooking. Although allicin is destroyed by cooking, many of the complex volatile sulfur compounds that were generated by the chopping or crushing (or their derivatives) remain. Whether one is preparing a sauce, stew, or stir-fry, chopping garlic and cooking it in oil is a fundamental step.
My favorite way to enjoy garlic is to chop it and sauté it in olive oil until it begins to turn straw-colored to light tan. Classically Mediterranean, garlic and olive oil are healthful and splendidly compatible from a culinary standpoint, creating a wonderful synthesis. Fine chopping or crushing releases the most flavor, but I sometimes leave a portion of the garlic in larger pieces in order to get a toothy bite. Cooking the garlic to a straw color both sweetens and deepens the flavor. Do not cook it to a deep brown, or worse yet, burn it, or it will taste acrid and unpleasant. The garlic should not steam, and lightly salting it helps bring out the flavor. This method brings out fine flavors from even the blandest cultivar and helps even the most sulfurous and aggressive cultivars taste rounded and nutty. With a Rocambole or Purple Stripe cultivar, the flavors are ambrosial. When I want to evaluate the taste of a new cultivar, this is one of my favorite ways to prepare it. Sautéed garlic is excellent with a good hard roll or crusty bread and makes a good side condiment on the dinner plate. It can be enjoyed by itself with bread or as a flavoring for other food such as grilled steak or sautéed fish fillet.
Cooking chopped garlic in oil can be readily adapted and extended. For example, after the garlic has sautéed briefly, you can add pole beans from the garden—or broccoli, zucchini, or greens such as chard, beet greens, spinach, and the like. How long the garlic should be sautéed before adding the vegetables depends on the heat of the pan and the length of time the vegetables will take to cook. The garlic should not steam and remain white or else the rich, nutty flavors will not develop. The idea is to end up with vegetables that are cooked but not overcooked, and garlic that has a light straw color. Regulating the heat of the pan and timing the addition of the vegetables are keys to success.
In another variation, after the garlic has turned straw-colored, add chopped arugula, or chopped basil, or a variety of other ingredients to suit your whim—perhaps a squeeze of fresh lemon—and then toss with pasta and finish with grated Romano or Parmesan. Or cook the garlic in peanut oil in a wok, add vegetables, then fish sauce or soy sauce, and toss and stir periodically until done. And so on. One quickly gets the hang of this technique after a time or two. It is applicable to many cuisines and well worth mastering.
Roasted Garlic
Roasted garlic has broad appeal. Its mild, sweet, somewhat caramelized taste is less intimidating to those with timid tongues. Because the garlic is not chopped or crushed prior to roasting, allicin and other volatiles are never produced, so the broad range of aromatic compounds and therapeutic benefits are not realized. This is not to say that roasted garlic is bad, however. It is certainly enjoyable, and the roasting adds to the range of ways that garlic can be enjoyed.