The Science of Cooking With Garlic

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Pressing garlic releases the enzyme alliinase, forming the sulfur compound allicin, which is responsible for garlic’s complex flavor. 
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“The Complete Book of Garlic” is the most comprehensive and in-depth guide available to what surely should be the next gourmet frontier. From 'Ajo Rojo' to 'Zemo,' Ted Jordan Meredith presents illustrated profiles of nearly 150 cultivars. Detailed chapters cover natural history, the history of garlic in cultivation, the nuances of cuisine and culture, therapeutic benefits, plant structure, how to cultivate, curing and storage, taxonomy, pests and diseases and chemistry. 

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.

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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, nam pla (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 alla carbonara:

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.

Roasted garlic is a tasty spread for crusty bread or toast and is even good in mashed potatoes. I confess, however, that the ubiquitous garlic mashed potatoes served in restaurants have ruined any affection I might have had for the dish. Garlic mashed potatoes may benefit a restaurant more than its customers, since it offers the opportunity for the restaurant to appear trendy and a bit daring while reaping the convenience and efficiency of maintaining the starchy glop on steam trays throughout the restaurant’s operating hours. If the garlic is not adequately roasted prior to joining the potato mass, the flavors can be particularly sulfurous and unkind. No skill or effort is required on the part of the line cook other than ensuring that the mass falls from the scoop and onto the victim’s plate. Roasted garlic deserves better.

There are various methods of roasting garlic. Here are a few. Remove the outer skins from a head of garlic and then slice off the top of the head so that the clove tips are exposed. Drizzle the exposed tips with oil, cover in foil, and roast at 350?F (175?C) for about an hour. As a variation, add about a tablespoon of water after the oil. In the last 15 minutes of cooking, uncover the garlic and baste with the juices. The heat and cooking time required will vary depending on the size of the heads and your preferences. Dry roasting individual cloves in a fry pan is another approach and yields garlic that is more toasty and toothy, less caramelized and pasty. Place unpeeled cloves in a skillet and toss and turn periodically for about 8 to 12 minutes until the skins have browned. Vary the time and browning according to the size of the cloves and your preference.

Peeling, Crushing, Chopping and Mincing Garlic

Peeling garlic cloves can seem like an onerous chore, particularly if you like to use a lot of garlic in your cooking. Nonetheless, once you acquire a certain rhythm and efficiency the task becomes quick and automatic.

If a clove is relatively easy to peel, and if your fingers are fairly strong, simply pinch the clove between your finger and thumb, positioning either your finger or thumb along one edge of the clove. This causes the skin to buckle, crack, and pull away from the flesh. You can then use your thumbnail to pull away the root end or tip end of the clove and gain a purchase on the skin to begin separating it from the flesh.

A standard and more effective variation mentioned earlier in the chapter calls for placing a clove on a cutting board or similar surface, laying the flat of a chef’s knife on top of the clove, and lightly whacking the knife with your fist or the palm of your hand. This buckles and cracks the clove skin and separates it from the flesh, making it easy to gain a purchase on the skin and peel it away. This is the method I most frequently use and recommend.

There are further variations on this basic method, from just tapping the flat of the blade to barely begin the separation, to giving the flat of the knife a good slam, flattening and thoroughly crushing the clove in the process. Crushing the clove immediately produces allicin and other volatile compounds, releasing the garlic’s tumult of complex aromatic flavors. At this point the flesh can be stripped off the skin and further minced or crushed. The skin can be removed and discarded with varying degrees of effort depending on the particular cultivar, its age, and the degree to which the flesh and skin stick to one another. I prefer to buckle the skin and remove it before smashing, crushing, or mincing the flesh, since to my mind this is cleaner and less wasteful, and since it ultimately requires no more time. But it is a matter of personal preference.

In the marketplace one can find various tools and gimmicks for peeling garlic. I do not have much use for them. Once simple techniques are mastered there is little need to complicate the process under the guise of simplifying it.

On the other hand, I frequently use a garlic press if I want crushed garlic rather than minced garlic. One can also fully smash a clove with the flat of a chef’s knife, and then quickly mince the smashed flesh with the knife’s cutting edge. Professional chefs use both methods. It is a matter of personal preference, one’s mood, and the tools that are handy. Garlic press manufacturers usually emphasize that no peeling is necessary. Although this may be true, some waste is inevitable, and there is often more mess. Artichoke cultivars, including standard supermarket garlic, suffer least if peeling is omitted. Many other cultivars have thicker skins and so require more hand strength and generate more waste and mess. I almost always peel garlic before crushing it.

Chopping and mincing are alternatives to crushing. Crushing ensures the maximum production of allicin and other volatiles, releasing all of the garlic’s aromatic pungency. It also allows the garlic to be distributed thoroughly and evenly with other food. Crushed garlic is ideal for mixing with a dressing for fresh lettuce or other greens. It works well in other venues as well, but sometimes chopped or minced garlic is preferable. Cooked in oil until straw-colored or light tan, chopped or minced garlic takes on a wonderfully rich, sweet, nutty character. Chopped garlic is coarser than minced garlic and in larger bits. Mincing creates more of the aromatic sulfur compounds and is more flavorful in this regard, but a toothy bite of more coarsely chopped garlic is good as well.

Chop or mince garlic as you would other foods. No specialized technique is required. Use a good chef ‘s knife, or Asian equivalent, for the purpose. An 8 in. (200 mm) chef ‘s knife is a good all-around size for the kitchen, and with a bit of practice one can make quick work of slicing, chopping, and mincing. One sometimes sees a cook using a small knife for such chores–and indeed, with small cutlery they do become chores. Paring knives are for paring; chef ‘s knives are for chopping and mincing (and many other tasks as well).

Garlic Presses

If you decide to use a garlic press, get a good one. A garlic press should be well made so that it can withstand extended use. The plunger should fit with little gap on the sides and fully extend into the chamber, so that the garlic does not escape up the sides but is thoroughly forced through the holes, leaving little wasteful residue at the bottom. The chamber should have many small holes so that the garlic is thoroughly crushed, but the press also needs to be compatible with your hand strength. More strength is required to force garlic through tiny holes, but better handle designs provide greater leverage and easier gripping. The press should also be easy to clean. Some form of plastic device with protuberances that match the holes in the chamber to push out the remaining residue usually fills this role. These seem like simple and obvious requirements, but it is surprising how many presses fall short in one way or another.

Avoid the kind of press with a cylindrical chamber and a plunger that is screwed downward, slowly forcing the cloves through a perforated bottom. This device is slow and cumbersome–and hopefully nobody actually keeps half-crushed garlic in the press waiting for tomorrow’s dinner.

The Swiss-made, cast-aluminum Zyliss Susi is a longstanding classic. Mine is decades old and has withstood extensive use. The handle and plunger pivots are sturdily made from large-peened pins. On the downside, the chamber is on the small side, it requires a fair amount of hand strength, and the handle is a bit too short and angular for the best leverage and comfort. I also have a press of similar design that was manufactured in Taiwan. The handle is more comfortable, but the press is not as well made. The handle and plunger pivots are not peened pins and are less robust. The handle pivot on mine has worn, and the two halves of the press now slip apart. The press is still quite usable but is a bit of a nuisance.

Unfortunately for classicists, the Swiss-made Zyliss Susi is no longer produced. It has been replaced by two models that are manufactured in China. The Zyliss Susi 2 has a pinned hinge design for the handle, similar to the original. The plunger itself has protuberances that match the holes in the chamber, but they only penetrate partway and do not purge the residue. There is no separate cleaning device, and the press is very difficult to clean. It is either a poor design or a good design poorly executed. The second model is the Zyliss Jumbo. It has a handle and plunger pivot design similar to my Taiwanese model that eventually wore and failed, though the Zyliss Jumbo appears to be far more robust in design and construction. The chamber is large and easily handles multiple cloves. The handle design is comfortable and provides good leverage. The plastic cleaning device that comes with the press works well. On the negative side, the nonstick coating reportedly wears away in the dishwasher. However, since I do not wash my press in the dishwasher, this has not been a concern. The Zyliss Jumbo is currently my primary and favorite garlic press, though I cannot yet vouch for its longevity.

The increasing enthusiasm for garlic has resulted in many new garlic presses coming to market. Several models that I have seen look promising, though I have not yet tested them.

Garlic Botulism

The title of this section could be “Storing garlic in oil,” but “Botulism” gets quickly to the point. Having garlic preserved in oil on hand seems like a good idea, but in fact it is a very bad idea. Garlic is a low-acid vegetable. A clove of garlic has a pH range of 5.3 to 6.3. As with any low-acid vegetable, garlic is subject to botulism contamination if improperly preserved. It is certainly not unique in this regard. Other low-acid vegetables such as asparagus, green beans, beets, and corn are also vulnerable to contamination with botulism.

As it grows, the botulism bacterium, Clostridium botulinum, produces an extremely powerful toxin that causes the illness. Storing garlic in olive oil or any cooking oil is a seemingly logical preservation method, but it creates exactly the right conditions that support growth of the bacterium and production of the toxin. Clostridium botulinum thrives in moist, low-oxygen, low-acid conditions. The spores are resistant to heat. Room-temperature storage conditions increase the risk and rate of growth. In North America at least three botulism outbreaks have been attributed to garlic-and-oil mixtures. Cooking garlic does not necessarily eliminate the threat. Roasted garlic stored in oil, for example, is still subject to the same risk. Although storage at room temperature increases the risk of contamination, long-term refrigerator storage does not remove the threat.

Commercially prepared garlic-and-oil mixtures are subject to stringent protocols and must contain citric or phosphoric acid to increase acidity. Do not attempt a similar process at home. There is no easy and reliable home method that can be performed with sufficient consistency and certitude to overcome the lethal risk.

A pH of 4.6 or lower does not support the growth of botulism, so storing garlic in vinegar is safe. On the other hand, you might not want to bother with acidified storage in any case. Storing whole cloves of garlic in vinegar destroys the alliinase and thus the possibility of producing allicin and related volatiles. Putting chopped or crushed garlic in vinegar allows temporary preservation of the volatile sulfur compounds, but the volatiles diminish at varying rates over time.

In short, storing garlic in oil is unsafe for the home gardener and cook, and commercial preparations often lack culinary merit. Garlic in oil, particularly olive oil, is an outstanding culinary marriage, but it is important to remember never to use oil as a storage medium for garlic (or, for that matter, for asparagus, green beans, beets, corn, or any other low-acid food).

This excerpt has been reprinted with permission from The Complete Book of Garlic by Ted Jordan Meredith, published by Timber Press, 2008. Buy this book from our store: The Complete Book of Garlic.