Preserving food at home: Fermentation

4 main types of fermentation

Lactic acid (or lacto-fermentation)

Lacto-fermentation is the process for fermenting produce. Bacteria, such as Lactobacillus spp., convert sugars into lactic acid and release carbon dioxide, which creates bubbles in the liquid or brine. The lactic acid then moves into cells of the produce to acidify it.

Alcohol

Alcohol fermentation is the process of making wine and beer. Yeast will ferment sugars to produce ethanol under low or no oxygen conditions

Acetic acid

Acetic acid fermentation is the process for making vinegars and kombucha. After alcohol fermentation, bacteria convert ethanol and sugars into acetic acid.

Alkali

Alkali fermentation is the process for making fish sauce and natto (fermented soybeans). A fermentation process for protein-rich foods. Bacteria break down proteins and produce ammonia, creating a low-acid final product.

How to ferment your produce in six steps

This section describes how to safely use the lacto-fermentation process.

1. Prepare the produce

1. Wash produce under cool running water.
   • Do not scrub the produce, as you may remove the good bacteria needed for fermentation.
2. Avoid peeling the produce.
   • For leafy vegetables, you may remove the outer leaves.
3. Cut or shred the produce if needed after washing.

2. Brine the produce

• Produce can be dry or wet brined. You will need enough brine to fully cover the produce. Make sure you have enough to keep the produce submerged in brine during fermentation. 
• Test the pH of the brine throughout fermentation. If there is too much salt in the brine, fermentation will not occur and the pH will not drop to become more acidic.

Dry brines

Dry brines (also called direct or dry salting) are good for finely chopped or shredded produce, like sauerkraut, kimchi and grated carrots. To make a dry brine:

1. Add between 3 tablespoons and 3 tablespoons plus 1 teaspoon of salt per five pounds of produce.
2. Mix the salt and produce well and gently massage the salt into the produce. 
3. While massaging the produce, liquid may begin to appear in the bottom of the bowl. Add this liquid to the fermentation container with the produce. This will activate the Lactobacillus bacteria and begin fermentation. 

Wet brines

Wet brines work well for produce that is fermented whole or in large chunks, such as cucumber pickles, carrot sticks, peppers for sauce and most fruits. To make a wet brine for most vegetables:

1. Mix 1 to 3 tablespoons of salt per 1 quart (4 cups) of water. 
2. Cucumbers, onions and radishes may require up to 5 tablespoons of salt per 1 quart of water.

3. Pack the container

1. Place the produce and brine in the container you have chosen. Wear single-use disposable gloves when transferring the produce. 
2. Compress any cut or shredded produce and make sure to include the brine. 
3. Ensure brine is covering the produce. There should be 1 to 2 inches of brine above the produce. Add an additional amount of the 1 to 2 percent brine solution, if needed. 
4. If using a large container or crock, leave 4 to 5 inches of headspace in your container. It should be about 75 percent full. 
5. Weigh the produce down if needed. 

4. Make the container airtight

The fermentation container should be airtight. 

• To make your container airtight, first wipe the rim of the container. If your container has a lid, place that over the produce and brine.
• If you are using an airlock system, follow the manufacturer instructions and place on the container. 
• If you are using a fermentation crock or a plastic container, use a properly fitting lid. 
• If you are using a container that does not have a lid, cover the produce with a plate or tray. Weigh the plate or tray down with a bag of brine. If the bag leaks, the extra brine will be added to the produce.
•  You can also use a glass jar filled with water to weigh down the plate.

5. Store the container

Containers with fermenting produce should be stored in a dark place, as Lactobacillus are sensitive to light. If needed, cover the container with a dark towel to block light. Ideally, you will store your ferment at a temperature of 68 to 72 degrees Fahrenheit. You can use a thermometer to measure air temperature.

6. Monitor the fermenting produce

• Allow your product to ferment for 3 to 4 weeks. If temperatures are below 68 degrees Fahrenheit, fermentation may take 5 to 6 weeks. 
• Depending on the container, you may need to "burp" it. To burp a container, briefly remove or crack the lid to allow built up carbon dioxide to escape. The lid should only be opened briefly to limit oxygen from entering the container.
• Monitor the pH of the ferment.
  • When a pH of 4.60 or lower is reached and bubbling has stopped, the ferment is ready.  
  • If bubbling has stopped but the pH is still above 4.60, continue to ferment and check the pH every 1 to 2 days.