Fermenting Fruits & Vegetables: The Basics

So you want to try your hand at fermenting produce but don’t know where to start?

Here’s some of what you need to know and need to have.

1). A basic knowledge of lacto-fermentation.

Lacto-fermentation is a battle between good and evil — bacteria, that is. The lacto part refers to lactobacilli, or lactic acid bacteria (LAB), strains of which transform whatever you’re fermenting into something else. Cukes into pickles. Wheat into beer. Grapes into wine. Milk into yogurt. Sometimes other bacteria or yeasts are involved.

How does it work?

Lactic acid bacteria convert the sugar present in vegetables and fruit into lactic acid. Lactic acid inhibits the growth of bad bacteria because it creates an acidic environment. Its production promotes an anaeorbic (without air) environment, and it serves as a preservative, maintaining the qualities of fermented foods. Finally, it is what gives fermented foods that distinctive sourness.

Harmful bacteria hate the conditions caused by lactic acid, but LAB love them. Your role is to ensure that the environment is just right for whatever you’re fermenting by encouraging LAB and discouraging intruders.

A byproduct of LAB consuming sugar and creating lactic acid is carbon dioxide, which helps maintain an anaerobic environment by forcing air away from a ferment. It’s why naturally-fermented veggies are a bit fizzy and why naturally-fermented beverages, like beer, are carbonated.

2). Salt.

You can ferment with other things, like whey (yes, that whey) or starters, but salt makes for a great texture, a tasty end-product and a safe environment. If you’ve never fermented before, start with salt.

Produce can be fermented in a brine (salt water) or dry salted, which creates its own brine. Dill pickles are in brine from the get-go, but sauerkraut starts as shredded cabbage mixed with salt. The salt draws the liquid out of the cabbage and creates brine early in the process.

A ferment requires a brine of a certain strength, which indicates the % of salt to water by weight. A brine of 5%, for example, contains 5% salt and 95% water by weight. I always use a 5% brine for New York-style garlic dill pickles, and a 3% brine for carrots.

Salt inhibits the growth of harmful bacteria but allows LAB to proliferate. Unless there’s too much of it. Then it stops fermentation altogether. The idea, then, is to concoct a brine that keeps nasties from catching hold while allowing the fermentation process to move forward at an optimal rate — neither too slowly nor too quickly.

Mineral-rich, dry sea salt, like Celtic or Himalayan pink, are best. Don’t use salt with iodine, anti-caking agents or other additives. Table salt is verboten.

3). Water.

Spring water helps ensure the best texture and flavor of the end-product and keeps ferments pure. It contains minerals but not chloride, chloramines, fluoride or other additives found in municipal water supplies that might inhibit fermentation or contribute off-flavors. While chloride is easy to evaporate out of water by allowing it to sit at room temperature for 24 hours or by boiling it for 15 minutes, and chloramines can be given the boot by the right kind of charcoal filter, fluoride is more stubborn. The process of removing it, for example by reverse-osmosis, also filters out minerals, leaving you with dead, or mostly dead, water. Many people use this super-purified water to ferment. I do not.

Speaking of dead water, there is bottled distilled water available. While some use this stripped-out H2O for their ferments, I don’t, and its use is the subject of debate in the fermenting community.

While I have certainly made many successful batches of pickles using Pennsylvania well water or New York City or San Francisco Bay Area tap water, it’s always best to control your environment to avoid absolute failure. Which can happen. Like if your well water has too high a mineral content, or your tap water is loaded with chlorine.

I find that spring water is the best choice.

4). Fermenting containers, airlocks and weights.

Fermenting requires an anaerobic environment, meaning “without air.” An appropriate vessel outfitted with an airlock and weights accomplishes this.

Back in the day people used the open method, meaning no airlock. I did this for years. It was how I learned.

While many still ferment in a plain old crock with a kitchen towel as a cover, I don’t. An airlock makes things less prone to trouble and, consequently, safer. The upkeep of the ferment is also much less labor-intensive.

Why is this?

An airlock allows CO2 and other gasses that develop to escape but does not let outside air in. It makes sense when you think of all that pressure working its way up out of the airlock. Air outside your fermenting vessel is simply not powerful enough to get down past it. No outside air means less exposure to harmful bacteria.

Weights keep whatever you’re fermenting safely under the brine. Anything sticking up out of it is subject to attack by said undesirables that will proceed to work their way down and destroy your entire batch of pickles. Molds, for example.

Weights are almost always used, even if an airlock is not.

There are fancy setups you can buy that come with everything, and ones you can jury rig. There are so many options that it is outside the scope of this post to name them all.

For now, I’ll talk about two: mason jars and fermenting crocks.

To use a mason jar, all you need in addition to a two-quart, wide-mouth jar is a fermenting lid of some kind with a built-in airlock or a canning lid outfitted with a hole, a grommet and an airlock. Honestly, commercially-available fermenting lids are so much more convenient than dealing with old-fashioned, water-filled airlocks that I suggest investing the $30-odd for a good set. They take up much less headroom because the airlocks are flat rather than protruding skyward several inches, and make moving ferments around a breeze. Plus, there’s no water level to worry about. Easy Fermenter lids produced by Nourished Essentials do a great job. If you prefer to use Fido jars with clamp lids and rubber gaskets that allow for a truly airtight seal, you can buy drilled lids and airlocks from companies like Pickl-It. Fido fermenting lids are more difficult to come by these days, unfortunately.

Companies that sell fermenting lids usually offer glass or ceramic weights — often in kits, so you get everything but the jar. Sometimes you do get the jar. They’re readily available from myriad suppliers on Amazon, but take care to purchase lead-free products that are the right size for your jar. In a pinch you can use Ziploc bags filled with brine, though this is a last resort.

If you have funds for a true fermenting crock it’s a great way to go. Fermenting crocks look like traditional crocks but they have a water trough around the top into which the lid is placed. This configuration allows gasses from the ferment to bubble out through the water. All you have to do is keep the water at the correct level. The downside, other than price, is that they are heavy and fragile. I use 5-liter versions which I can move around fairly comfortably, but I’m very careful. You can often find 5-liter German-style crocks for about $60. If you want a true German-made crock, like Harsch, you’re talking money.

5). Other kitchen items.

If a plain-old kitchen scale would make for a good fermenting friend, then a digital kitchen scale would be a bestie. The former will weigh your salt, but the latter makes it easy to weigh it in your jar.

Why weight and not volume? Weight is more accurate. For example, flaked salt weighs less per tablespoon than granulated salt.

You can use only stainless steel, wood, glass, glazed ceramic, food-safe plastic and silicone for fermentation. Anything that comes into contact with your ferment — including the pot you boil your brine in, if boiling is called for — must be made of one of these materials. No aluminum or other reactive metals. No non-stick.

At the very least make sure you have a small mesh strainer for skimming and a pair of small tongs and a large bowl. If you want to get fancy, buy some stainless steel rings if you’re using mason jars to ferment or even to store. Brine will eventually corrode the aluminum ones.

The gadget canners use to get air bubbles out of their jars prior to processing is handy for fermenters, too. Alternatively you can use wooden skewers or the non-business end of a slender serving spoon.

A canning funnel will make your life easier when filling jars, and a bottle brush will help get them clean.

Ferments sometimes overflow, so a small hotel pan or sheet pan offers protection. Line it with a silicone mat so it’s not slippery. If you have a place for this set-up to live permanently, it can accommodate multiple jars. Most ferments won’t overflow, but you’ll want to protect your surfaces just in case.

Measuring spoons and liquid measuring cups are a must.

Disposable kitchen gloves are essential to protect hands from things like kimchi paste — and to lessen the chance of contamination with certain ferments.

6). Flavorings.

You’ll need flavorings. I could not possibly give you a complete list of the herbs and spices you might need, but I can assure you you will rarely need what is sold as “pickling spice,” so don’t buy that until you need it for a specific pickle. Start with black peppercorns, bay leaves, perhaps caraway seeds and juniper berries, if you want to make sauerkraut. Gachugaru, if you plan on kimchi. Red pepper flakes and dried whole chilis are helpful. Start simple, but please buy high-quality dry spices. Organic, if you can swing it. And don’t keep them beyond their potency. I store the majority of my herbs and spices in the refrigerator or freezer to protect them from heat and light.

There are only two fresh ingredients I’ll list here: flowering dill and garlic. And I mean heads of garlic. With these two ingredients, a few peppercorns, Kirby cucumbers and brine you can make fantastic New York-style garlic dill pickles.

Finally, if you can get your hands on oak, horseradish or grape leaves — wonderful! If not, lay in some black tea leaves and do-it-yourself teabags. These leaves are rich in tannins, and will help certain vegetables, like cucumbers, remain crisp. The bags will prevent floating leaves, and are also handy for loose spices.

7). The right weather.

Ambient temperature plays a major role in the fermentation process. The warmer it is, the faster it goes, and “fast” is not a virtue here. A slow ferment will produce complex flavors and firm pickles. A fast ferment often results in the opposite.

The ideal temperature range for fermenting produce is roughly 64 to 72 degrees Fahrenheit. If you want to ferment at 76 degrees, you need to take precautions to keep things safe. Remember the rule about salt? That if you increase the percentage of salt in your brine it slows fermentation? When dealing with warm weather, then, which accelerates fermentation, you would counteract it with something that slows it down — like, say, using a 5.5% brine versus a 5% brine. Got the idea?

If you’re looking at 80 degrees, it’s simple: don’t ferment produce.

I ferment in the coolest spot in my home when the temperature range is acceptable. In my last house that was the corner of my bedroom. In my current house, it’s the garage, which I’ve insulated.

You may be wondering what’s to be done if a ferment is started on a cool day but a heat wave floats in before it’s finished. It depends. The longer the ferment had to develop at a normal rate the better it will be at handling future temperature spikes, though very hot weather that hangs around will almost certainly ruin it. It’s one of the reasons I have an extra fridge — to rescue pickles. The fermentation process will fall well below a snail’s pace at the average temperature of a home refrigerator, but that’s far better than having to toss the whole batch.

8). A watchful eye.

Ferments must be closely monitored to ensure there are no nasties developing on the surface of the brine, and you’ll need to learn the difference between what’s harmless and what isn’t.

Kahm yeast generally presents as a white, flat film and/or white blotches and can be skimmed off. Unless you have a yeast sensitivity it’s not harmful to eat, but it is best removed so it doesn’t add off-flavors.

Mold, on the other hand, is harmful — especially if it’s been allowed to propagate unattended. It’s green, black, red or pink and generally thicker than Kahm yeast and often fuzzy or hairy, and first shows up as dots or specks.

There’s controversy about the safety of skimming surface mold. Some believe that once it’s present on the surface, it has already permeated the entire ferment. Others believe that it’s fine to remove floating mold if the pickles are fully submerged and things smell as they should. Some think it’s fine to scrape mold off one part of a fermented vegetable and eat the rest.

I check my ferments daily, and if I see anything starting to form at the surface, I skim.

Given that undesirables begin making their mischief at the surface, I do not believe that a tiny speck of mold that formed overnight would have had a chance to reach whatever I’m fermenting because of how well I submerge my pickles and how careful I am about the fermenting environment in general.

However, I’m not making a recommendation about how you should handle mold, if it appears, only that you follow safe fermenting guidelines and spend time reading up on the issue in order to make an informed decision.

There’s no reason to wind up with a carpet of mold — which would happen if you, say, left a batch of fermenting cukes unattended during a lengthy period of warm weather. The whole thing would need to be discarded. And carefully.

Clean vessels, the freshest produce, the right water, the correct brine strength, an airlock and weights, a conducive ambient temperature and frequent checks are all essential to avoiding mold.

That said, you may not be able to avoid problems 100% of the time, because this is, after all, a natural process that can be unpredictable and you are not a controlled commercial operation. But you can certainly minimize their likelihood. As you become an experienced fermenter you’ll need to rely on research and outcomes to guide you. I suggest logging all variables at the start of each ferment, as well as daily progress. If a problem arises you’ll then have a better idea of what may have been the culprit. Once you have everything down, you won’t need to log more than start and actions dates.

9). The ability to follow instructions, measure accurately and work clean.

I probably should have made this the first item. If even one of these requirements is not in your nature, fermentation is a poor choice. No judgement whatsoever, as we’re all differently inclined, but this is not an undertaking where creativity trumps all. While there are countless ways you can let your artistic side loose on a batch of cherry peppers, you have to do so within safe parameters.

I could not possibly list everything this means, but here are a few-big ticket items:

1). Brine strength needs to be accurate. You can’t “eyeball” it.

2). Get your recipes from a reliable source, and don’t deviate from them at all until you know what you’re doing. This reminds me of a dill pickle recipe my Mom made back in the 1970s, right when she started with food preservation. She thought it would be interesting to add sugar to the brine. The pickles didn’t think so, and promptly failed. A half-bushel of them.

3). Your hands and workspace need to be very clean. You do not have to use gloves to work with most ferments. Very clean hands with short, unpolished nails are fine. If you have polished nails, use gloves. I only wear gloves when I’m working with a large quantity of very hot peppers, or pepper pastes.

4). Vessels, lids and weights must be very clean. Not sterilized, but washed with hot water and dish soap and rinsed in hot water. Running mason jars through a dishwasher is fine, but make sure you don’t have any sediment from dishwasher soap.

5). Everything that comes into contact with your ferment should be washed and dried appropriately shortly before use.  For example, if you find that you must skim, utensils should be washed in hot water and dish soap and dried directly beforehand. If you need to swap out weights, ditto. You don’t need to autoclave this stuff, but you’ll want to make sure that there are no bits on your utensils from last week’s beef stew.

6). If you taste the brine, you cannot double-dip. If you want to taste it twice you’ll need two spoons. This goes for finished ferments and any other type of preserve.

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