An old sign painted on cardboard at Thirty Acre Farm. Credit: Gabor Degre | BDN

As products like kimchi, kombucha and kefir gain in popularity on restaurant menus and market shelves, more and more people are looking to try fermentation ― an age old method of food preservation ― in their home kitchens, according to a local food preservation specialist.

But like any method of food preservation, food safety is a concern. With trendy ferments introducing more and more folks to the process of fermentation, it’s important that people understand the science behind fermentation before trying to it themselves.

“With any home preservation there is always a concern around workspace cleanliness. There [are] just less safety steps or controls in place at home than there are at a production facility,” Kathy Savoie, of University of Maine Cooperative Extension said. “People need to understand what is going on with fermentations and that salt, moisture, oxygen levels and temperature are all a part of the equations that needs to be followed closely to make sure in the end you have a safe product.”

Unlike other methods of food preservation, such as canning, that focus on getting rid of microorganisms, the process of fermentation uses microorganisms to break down the cell structure of the food item and preserve them in an acidic environment. Traditionally fermented food items that have the most research and reliable recipes associated with them are pickles, sauerkraut and yogurts, according to Savoie.

Through fermentation fresh, raw produce is combined with salt, which causes the produce to wilt and sweat. The liquid formed in this process creates an anaerobic environment, where healthy bacterias break down the produce creating lactic acid that helps to preserve the food long term. If done correctly, the acidic environment created during fermentation prevents harmful bacteria from growing.

Since fermentation breaks down complex carbohydrates, turning them into simple naturally occurring sugars, Savoie said fermented foods are beneficial to the body’s digestive system ― a health benefit that draws people including fermented foods into their diet.

To start making fermented foods at home, your equipment and workspace must be sanitized and your hands must be clean to prevent any outside bacterias from entering the fermentation process. It’s also important that food-grade containers are used to ferment in, this can either be a sanitized food-grade five-gallon bucket or a traditional sauerkraut crock.

The produce that you ferment should also be at peak quality, Savoie said. When fermenting, canning and pickling salt must be used in place of traditional table salt.

While recipes for fermentation vary based on what you are fermenting, it is always important to obtain recipes for fermented food from a trusted source, Savoie said, to ensure that the conditions created by the recipe ingredients and proportions allow for safe acidic conditions that prevent the development of harmful bacteria. During the fermentation process, exposure to oxygen should closely be monitored and prevented by pushing the fermenting produce below the liquid in the container. Savoie said food-grade plastic can be placed and pressed on top of the produce during fermentation to keep air out.

Temperature is another control during the fermentation process. Between 70 and 75 degrees is the ideal temperature for fermenting foods, though Savoie said it is hard to maintain this temperature over the weeks it takes for food to ferment. If the temperature dips below this range, fermentation will take longer, and if the temperature is any warmer, the final product will become soft and undesirable, she said.

To store fermented foods, pack the final product into food-grade containers. If storing in the fridge, fermented foods can be stored for one to two months. To make the product shelf stable, prepare a boiling water bath and place the packed containers into the bath for 20 minutes.

If at any point during the fermentation process off odors or colors develop, Savoie said not to chance it by tasting it. “A lot of things have advanced in the realm of food safety, but one of the things that hasn’t is the old adage, ‘When in doubt, throw it out.’”