[Photographs: Vicky Wasik]

Editor's Note: Please welcome Christina Ward, a master food preserver for Milwaukee County in Wisconsin and author of Preservation: The Art and Science of Canning, Fermentation and Dehydration. Over the next few weeks, she'll break down the science of and principles behind food preservation, with accompanying recipes so you can put your newfound knowledge to work.

Place a finger anywhere on the globe, and I guarantee you that the local cuisine features some kind of pickled something. I will also guarantee you that the pickle you eat in Nairobi will taste similar to the pickle in Berlin, which is also akin to the pickle in Hokkaido. But why?

The answer is acid.

Let's establish some common vocabulary. This is harder than you may think because of how the word 'pickle' is used. First, it's a verb. To pickle something is to submerge it in an acidic solution or a solution that will become acidic. We (meaning every single English speaker on Earth) also use 'pickle' as a noun to refer to things that have been in that acidic solution. Because what is placed in that solution is so infinitely variable, the noun form of pickle can lead to funny misunderstandings. In North America, we call a pickled cucumber, a pickle. In England, pickle is an acidified spread made of mixed vegetables. Confused? Let's back up even further. Why in the heck have people been putting their food in acid and acid in their food for thousands of years?

Acid Battery

Food preservation works by erecting chemical and physical barriers to pathogen growth, kind of like when Batman (Adam West, thank you very much) threw chairs at the Penguin's minions during chase scenes. Raising the acid level in food is the best chair we can throw at microbes. But not all acids are created equal—a wide range of acidity levels are possible, from very weakly acidic milk all the way to incredibly potent hydrochloric acid. For an acid to be useful to us, we need to identify the ones that are both palatable as food yet strong enough to kill microbes.

We use the pH scale to measure how acidic or basic a solution is, and that scale ranges from zero to 14, with seven being neutral (neither acidic nor basic). Confusingly, the lower the pH number, the more acidic it is, so a high-acid food will actually have a low pH. Most of the foods we eat fall within the pH 2 to pH 7 range. The good news is that microbes are more sensitive to acid than humans are; their preferred range is a pH of 4.5 to 10.* This is good news because it leaves us with the range of pH 2.1 to 4.5 in which our foods will be safe from microbial infestation yet still tasty to eat.

* Some people will say that microbes won't really be able to survive until the pH hits 4.6. I say that's a little too close for comfort, so it's better to err on the side of caution and bring that measurement down to 4.5 so we can feel secure that our food is solidly in the safety zone.

We've just identified a giant hammer in our food preservation toolbox: Changing the acidity of a food to within a range that is hostile to microbes yet palatable to humans extends the useful lifespan of that food.

Let's Get pHysical

Back to our pH measurements. The accepted pH range of food is about pH 2 to 10. So an acid with a pH of 1.8 is too acidic, and will cause burning in your mouth and throat. Really! (The same is true of highly alkaline substances; lye burns, for instance, are nasty, nasty injuries.) How can you determine the pH of your food? Measuring pH can be done by the home cook with one simple tool. No, not those little strips of litmus paper—their color changes can be difficult to read correctly. A simple digital pH meter does the job nicely. They can be found at home brew stores or online. I like and recommend the Hanna Checker Plus; it's relatively inexpensive and reads to the hundredth decimal point. Let's be clear: You don't need a pH meter to make pickles, but having one is extremely helpful for adventurous and experimental pickle makers, as it gives you the information you need to make sure your pickles are in the safe zone. The rest of us can rely on trusted recipes and a few key principles and ingredients to make pickles safely at home.

Either way, we should all get to know our culinary acids. Acetic (or ethanoic) acid is the key component of vinegar; its pH measurement is approximately 2.4 at the 5% concentration found in most vinegars. Citric acid is found in all citrus fruits, but the ones used most often for preservation—lemon and lime juice—have a pH measurement of about 2. Tartaric, malic, and oxalic acids are found in tea, apples, stone fruits, and grapes. Those foods have an approximate pH range of 3 to 5. Out of all of these, acetic acid is the most useful to us when acidifying foods.

Wait! I know what you're going to say next: What about lactic acid? Lactic acid is created by the lactobacillus bacteria during the fermentation process that's essential to making yogurt, kefir, sauerkraut, and more. Lactobacillus is an 'acidophile,' which means it prefers to live in a slightly acidic environment. That's great for humans because lactobacillus not only doesn't cause us harm, but can also be beneficial to our digestive system. So yes, lactic acid creates an acidic environment that extends the life of a food, and we'll talk about lacto-fermentation a bit further along. Promise. But for now, acetic acid.

Acetic Arts

Making the vinegar brine for vinegar pickles, and prepping the jars for packing.

So what is acetic acid? A cursory examination would immediately reveal that a solution of acetic acid is colorless and has that unmistakable and pungent distilled-vinegar scent and sour taste. Producing it is a two-step process. First, a carbohydrate-rich organic material, like grapes, is fermented to make an alcoholic product, like wine. It's then fed extra oxygen to create an environment that is perfect for the acetobacter bacteria to move in and consumer the alcohol and produce acetic acid as a byproduct. I often explain it to kids like this: the poop of yeast is alcohol, and then acetobacter eats that alcoholic poop and poops out acetic acid. Gross, but true.

If your goal is to make wine, you don't want acetobacter around, since it risks turning your wine to vinegar, and there's not much fun in toasting an anniversary with glasses of that. But if your goal is to make vinegar, then you'd deliberately introduce acetobacter to your fermenting wine. The modern method is to oxygenate huge vats of acetobacter-inoculated young wine as it's fermenting to produce a final mixture that is between 15 to 20% acetic acid. That mixture is then diluted with water to reach a 5% acidity. So your jug of distilled white vinegar is 95% water and 5% acetic acid, with a pH measurement of approximately 2.4.

Vinegar can be made from any alcoholic beverage. Wine vinegar is made from wine (fermented grapes), while cider vinegar comes from hard cider (fermented apple juice). White distilled vinegar comes from a grain or potato mash and balsamic vinegar is made from aged, fermented grape must (the leftover solids from the winemaking process). Most vinegars have a 5% acidity, but some specialty and flavored vinegars are mixed with a higher proportion of water for an acidity of 4%. This can be problematic for food preservation because our goal is to raise the overall acidity of our food, and a lower-strength vinegar may not give us the oomph we need. In any pickling recipe worth its salt (or should that be vinegar?), it will specifically tell you to use vinegar that has a 5% acidity. You may have never noticed it before, but every bottle or jug of vinegar will have its acidity percentage printed on the label in small print.

Lactic Tactics

Lacto-fermented pickles sit in a saltwater brine that gradually grows acidic with the help of friendly bacteria.

Lactic acid is a kissing cousin to acetic acid with just a slight variation in its chemical structure. It rates as less acidic on the pH scale, coming in at approximately 3.2 as measured in a finished fermented pickling brine. Lactic acid is also a product of fermentation, but the process for making it is just one step. To use my kid-science: Lactobacillus eats carbohydrates and poops out lactic acid. (When we're talking about acetobacter and lactobacillus, we're referring to the genus of those bacteria, but it's good to remember that there are subspecies that produce slight variations in the taste of both vinegar and lacto-fermented foods. When you hear the word 'acidophilus,' what that means is that the fermentation is due specifically to the lactobacillus acidophilus bacteria.)

According to the Mayo Clinic, active lactobacillus bacteria can be beneficial to your health. If you freeze or heat-process lacto-fermented pickles, you'll kill a lot of the microbes, including just about all of the lactobacillus. The pickles will remain safe and delicious to eat, because their high acidity ensures that, but they'll lose whatever health benefits the live lactobacillus may have provided.

Pickling Time!

Let's move along to what is happening when we pickle foods, both with the acetic acid in vinegar or with lactic acid in a lacto-fermented pickle. Let's use cucumbers as our example.
When we soak cucumbers in a vinegar solution, the water in the cucumbers is gradually drawn out through osmosis into the pickling solution, which then becomes diluted. Meanwhile, the acid in the pickling solution slowly penetrates into the cucumbers. The acidity of the pickling solution is reduced overall, but the acidity of the cucumbers is elevated, rendering them safe from microbial infestation. The 'bad guys' are once again thwarted.

In lacto-fermented pickles, we start by making a brine from water and salt; that brine starts with a neutral pH of about 7. The cucumbers are placed into the brine, then weighted down to keep oxygen out. Lactobacillus, which lives all over the place, will find this crock of cukes in salt water to be the best house on the block and move in immediately. It helps to visualize the process as farming—you're the bacteria farmer creating the perfect environment within which your lactobacillus will grow. This is when the magic happens, with the lactobacillus eating carbohydrates (sugars) in the cucumbers and pooping out lactic acid. With every passing day, the solution becomes increasingly acidic, which means it becomes increasingly hostile to unwanted pathogens. Eventually it reaches a safe acidity, at which point your cukes are as good as preserved.

It takes about three weeks in a jar for a whole cucumber to reach peak pickle using a vinegar solution and about four to six weeks in a fermenting crock with a salt-water brine.

Making Things Interesting

So far we know that we can preserve our cucumbers and give them a tart taste with either a vinegar or salt-water brine. But what about other ingredients that can improve the flavor and aroma of the pickles? Spices are one of the most common options.

Dill pickles are so popular in North America that the most commonly used blend of spices can be purchased under the generic name, "pickling spice," though even that varies depending on where you live. This Dill Pickle recipe on Serious Eats has just a few of the spices that we use in the Midwest, where I live. That doesn't make the recipe 'wrong,' it's just another iteration that bears the loving fingerprints of place and culture. In the Midwest, our pickling spices reflect German, Polish, and Serbian traditions. We're partial to cloves, allspice, mace, anise, juniper, and loads of mustard seed and turmeric. There are no incorrect choices when it comes to pickling spices, but whether you create your blend from scratch or use a premade mix, do take the time to get the freshest spices you can. I'm partial to my hometown purveyors, Penzeys.

Herbs like dill are another route to pickle flavor. I'm not sure if teenage boys still use 'dillweed' as a mild swear (they did when I was growing up), but dill weed is exactly what's needed for great pickles. It comes from the same plant as the young, feathery dill that's most common in grocery stores, but the "weed" is older and fully grown, often recognizable by its multiple flowering yellow heads. It's the flower that has the best flavor. During the summer pickling season, you'll sometimes see it in big bunches at farmer's markets and better produce markets. Often, it's labeled as "pickling" dill. Buy it. Use it. You won't regret it. (Of course, if you can't find dill weed, dried dill seed or the feathery baby dill will do in a pinch.)

Our last two ingredients, which are especially important for lacto-fermented pickles, are the water and salt themselves. The choices made here can be important to the success of your pickling. If you don't know much about your water quality, your best option is to use distilled water. Modern tap and well water are chock-a-block with additives (both wanted and unwanted) that can sometimes interfere with a successful lacto-fermentation. Where I live, our tap-water is off the charts with lead. Can you see where this is headed? If the goal is to ferment our cucumbers for a safely acidic result, then using water that might interfere with that could be a problem. That said, if you are lucky enough to have high-quality tap water, go ahead and use it.

It's best to use "pure" salt also. Canning salt, sea salt, pink salt, kosher salt—it doesn't matter as long as the label says it's pure salt. Table salt can be problematic as it's fortified with iodine and has additives to keep it from caking, both of which can cause clouding of the brine and discoloration of the pickles. This doesn't affect the ultimate safety of the pickles, but it makes them look unappetizing, which is not our goal.

Whether you want to add sugar in vinegar pickling situations is a question that's open for debate. The argument in favor of sugar is that it balances out the vinegar's sourness, creating a more pleasant, well-rounded flavor. I prefer them without any sugar, but I also loathe sweet bread and butter pickles. Of course millions of people love them, which is really just a way of saying that it's a matter of taste. And for anyone who read my article about the role of sugar and salt in reducing water activity for food preservation, rest assured, that's not their role here: The acidification of the food more than covers our food-safety bases.

Another optional ingredient is onions, though I'm confident that a fair amount of people will say that onions are never optional! (People either think onions must be in everything or should be obliterated from the planet.) The Eastern European-influenced picklers among you will want to add thinly sliced rounds of white onions, as I do in my recipes here.

Much has been written about the 'blue-green garlic phenomenon'; in fact, there's plenty written right here in this Food Lab article. A phenomenon specific to pickling, the teeny tiny residual amounts of copper in the vinegar or water can react with sulphur compounds in the garlic cloves and turn those buggers varying shades of blue and green. Don't lament if you find blue, green, or gray garlic cloves in your pickles! The pickles and garlic are safe to eat, though the garlic may taste bitter depending on the specific concentrations of sulphur compounds in the clove.

The last ingredient and star of the show is the cucumber. Not just any cukes will do—you need to find a variety that is suited to pickling. The ideal pickling cucumber is smaller than a slicing cuke with a pebbled exterior and less water inside. Look for Kirby, Excelsior, Wautoma, Jackson Gherkin, and other varietals for pickling. Talk to your local farmer or produce manager to find out if they're growing or getting pickling cucumbers. Farmers will ask you what size you want; the rule of thumb is more the rule of pointer finger: "Number One" pickles are the size of your pointer finger and command top price; midgets or cornichons are no bigger than a pinky-finger and are even more expensive; any cukes larger than your fingers are referred to as "Number Twos" and are, of course, cheaper. If you're looking to pickle whole cucumbers, get Number Ones. If you want to do slices or spears, Number Twos will work just fine.

Step-By-Step: How to Make Pickled Cucumbers

Step 1: Buy Fresh and Trim

The first step is to buy good quality, super fresh cucumbers. The most common pickle question I get is how to avoid mushy pickles. There are a couple of things that can cause this, but most of the time the culprit is age. Cukes from the grocery store are usually old. If you can, go to the farmers market and order your cucumbers fresh from the fields, so that they're no more than 24 hours old. As soon as you get them in your mitts, start making pickles. No delays. No goofing around! Those cucumbers started their march to decay as soon as they were harvested.

There are products on the market as well as folk-remedies to ensure crisp pickles, but using fresh cucumbers beats them all. Grape leaves, calcium chloride, alum, heck I've heard of people putting aspirin in their crock (please don't do that). Science shows us that most of these additives either don't work or introduce other problems to the pickle. Fresh is best.

The one trick for reducing cucumber softening that does work is to remove the enzyme residue from the flower-end of the cucumber. This little spot is the remnant of the blossom and is rich with enzymes that, when the cucumber is separated from the plant, accelerate decay. Get rid of it. Either slice off 1/8 inch from the blossom-end or gently scrape off the blossom end with a spoon or your thumbnail. That should be the first thing done to the cukes when you get them home. (And it goes without saying that you brought your cukes straight home to your kitchen without detours, delays, or stops at the ice cream shop.)

Step 2: Soak in Salt Water

After you've removed the enzyme deposits from the flower-end of the cucumber, place them into a brine of cold water and salt, using about 1 cup (250 grams/8 3/4 ounces) of salt per 1 gallon of water. As they soak, the salt works to draw out a bit of the water inside the cucumber, which helps make them even more crisp.

Step 3: Make Your Brine

To make a vinegar pickling solution, mix together water, vinegar, and salt; the ideal ratio is 3 quarts of 5% vinegar per 1 gallon of water and 1 cup of salt. For easy removal later, I like to put my basic pickling spice mix into a cheesecloth sachet or stainless steel tea strainer and then add it to the vinegar brine as well. A little heat helps dissolve the salt into the brine and more quickly extracts the pickling spice flavor, but make sure you cover the pot as any evaporation will throw the solution off, potentially rendering it overly salty and vinegary. After letting the spices steep for 15 minutes, I remove them, though how long you let your spices steep is up to you. It's just a question of how strong you want the flavor to be.

For the lacto-fermented pickles, you want to make a simple salt-water brine that's approximately 3.5% salinity, which is 35 grams of salt per liter of water. The process isn't so sensitive that you have to be quite so exact; different salts can vary in mass by volume, and yet you can still get away with measuring your salt by volume without messing your lacto-fermented pickles up. I find that warming the water to around 100°F (38°C) helps dissolve the salt.

Let both brines cool to room temperature before adding them to the cucumbers.

Step 4: Prep and Pack the Jars

Drain the cucumbers from the cold-water brine.

If you're going the lacto-fermented route, get your crock and gently wash it with warm, soapy water. None of this silly anti-microbial soap though, because we want microbes. We're not preparing for surgery. Don't despair if you don't have grandma's pickling crock. If you have a crockpot, you have a crock—just pull the insert out from the heating element and use that. Otherwise, a food-safe bucket or glass canning jars work too.

Next, build layers in the fermentation vessel, beginning with the dill flowers (if you have them), dill, some garlic, onion slices if you like, a layer of cucumbers, then sprinkle with some pickling spice. Repeat.

For vinegar pickles, quart canning jars work well and should either be washed with hot soapy water and then rinsed, or run through a dishwasher cycle. No need to dry them.

Packing cucumbers into a canning jar is a bit of an art. A visit to a county fair will reveal expert-level jar packs with beautiful, uniformly sized cucumbers perfectly lined up in the jar. If you plan on entering the fair, then do that. Otherwise, your goal should be twofold. The first is packing the cucumbers, whether whole or speared, as tightly as you possibly can without completely crushing them. The second is keeping the cucumbers below the shoulder-line of the jar. (The shoulder of the jar is that slight curve below the opening.) A test for a strong pack is to place the palm of your hand over the opening of the jar and tip it upside down. Yes, some of the spices will fall into your hand, but the cucumbers should not move. If they do, you need to adjust. Swap out a bigger or smaller cuke or give the bottom of the jar a gentle thunk on the counter to help them settle. The task of packing a jar is futzy but pays off in the end. Just like lacto-fermented pickles in the crock, these cucumbers need to stay submerged in the pickling solution. A loose pack results in the dreaded floaters. Those cukes won't be pickled and will turn mushy.

Step 5: Add Brine to Pickles

Adding vinegar brine to pickles.

For vinegar pickles, this is as simple as pouring your prepared brine over the tightly-packed cucumbers until they're fully submerged. If you're heat-processing the pickles, wipe the rims, put on the lids and bands. If these are intended to be refrigerator pickles, put on the lids and then put the pickles into the fridge.

For lacto-fermented pickles, you need to do a little more to ensure the cukes remain submerged. Remember, lacto-fermentation is an anaerobic process, which means exposure to oxygen in the air is your enemy. Start by pouring salt-water brine over the cukes in the crock to fully cover them. Then place a weight on top of the cukes to keep them submerged, followed by some kind of lid or covering.

There are commercial weights you can purchase that fit the exact interior diameter of a crock. Some families have a 'special' plate that is the correct diameter for their crock, and they weigh the plate down with something heavy. My husband still has the "pickle brick" his grandmother used to keep her plate submerged. For the rest of us, there's an easier way that costs nearly nothing: the water bag method. Simply fill a sturdy zipper-lock bag with salt water and seal it, pushing out as much air as possible. (The water in the bag doesn't touch food, but the salt helps prevent that water from getting icky.) Place that bag into another freezer bag of the same size and seal that one too. Then put the water bag flat across the cucumbers in the crock. The water in the bag is enough to keep the cukes below the brine. Cover the crock with a flour sack towel to keep out insects out, and that's it

Step 6: Store and Wait

If you want to heat-process your vinegar pickles, place the sealed jars into a pressure canner and process for 15 minutes. Otherwise they can go straight into the fridge. Whether processed or refrigerated, the cucumbers need to stay in their jars for about 3 weeks to transform into pickles. Processed pickles last 12 to 18 months on the pantry shelf while fridge pickles last about 2 months. (The shelf life of fridge pickles always depends on how cold the refrigerator is and where in the fridge you place them; the back of the refrigerator is much colder than the shelves on the door.)

One thing to consider about heat-processing your pickles is that the heat interferes with the holy grail of perfect pickles: the crispy crunch. Any time you process your pickles in a hot-water bath or steam canner, you're cooking them. And cooking will result in softer pickles. If your perfect pickle is akin to the Claussen or Vlasic brands you find in the refrigerator case at the market, then your only option for storing is in the fridge. If you choose to store your pickles in the fridge, it's a refrigerator pickle.

For the lacto-fermented pickles, the lactobacillus works its magic best at around 60°F (16°C) to 70&degF (21°C). Sure, it can get hotter than that during the summer, but that's also why folks keep fermenting crocks in basements or closets—somewhere that is cool and temperature consistent. Slow and steady gets you to the perfect pickle.

Check them every three days during active fermentation to ensure that nothing unwanted is happening in the crock. How do you know if something is bad? Well, you can see it. The cucumbers will turn gray and be disgustingly mushy. Sometimes you'll see a white mold-like substance bubbling on the surface; it's not mold but yeast. This is often called the scum. Having a yeast growth can adversely affect the flavor and quality of a pickle. Uninvited yeasts and molds compete with the lactobacillus, which means that your fermentation may not be producing enough lactic acid, which of course means it's not safe from harmful microbes. Some folks will skim the scum and keep on fermenting, but why? Our goal is perfect pickles, not kinda, sorta good pickles. You can skim if you want, but not me. On the other hand, if you see blue, green, pink, or black mold, that's it; the party's over. Molds are generally bad news. Sure, some people even scrape that stuff off, but I don't like to take those risks with food that I give to my family and friends. Compost that batch and start over.

How long will it take? Unknown. Deciding when your pickles hit their peak is a subjective and personal measurement. After about 3 weeks of fermentation, your pickles will start to look and smell, well, pickle-y. If you're a fan of half-sours, this is when to place them in the fridge to slow the fermentation. If your tastes run more to the full-sour end of the spectrum, keep on fermenting, my friend: you've got another couple weeks until you get there. This is also the point where you need to decide what you're going to do with all your pickles. Storing them in the fridge keeps the lactobacillus alive but slows the fermentation process. If you put them into jars and then process them, they'll last for a year in the pantry, but the lactobacillus is dead (and, as with the vinegar brine, the pickles will soften in the heat).

That's it. Pickles. Using these methods and recipes one could literally pickle shoes. As with any chemistry project, keep your ratios exact and your equipment clean, and you will have Batman-approved perfect pickles.