Kimchi is the national dish of South Korea and has become a global trend in the last several years. With its distinct and pungent odor, people seem to either love this stuff or despise it with all their passion. Kimchi is a mixture of vegetables and seasonings that is fermented before it is eaten. It is spicy, salty, and tangy all at the same time.
So how do you make kimchi?
Cabbage is chopped up into large pieces and soaked in salt water allowing the water to draw out from the cabbage. Other seasonings such as spices, herbs and aromatics are prepared. Ginger, onion, garlic, and chili pepper are commonly used. The seasonings and cabbage are mixed together. Now the kimchi is ready to ferment. The mixture is packed down in a glass container and covered with the brining liquid if needed. The kimchi sits at room temperature for 1-2 days for fermentation to take place. During fermentation, microbes convert sugars found in the food into various acids, alcohols, and gasses, changing the flavors in the food. Once fermentation is complete, the kimchi is placed in the fridge. Though this slows down the fermentation process, many changes in the bacteria communities and metabolites occur in the upcoming months that can alter the taste of the kimchi.
In the making of other microbial foods such as bread, yogurt or kombucha, a “starter culture” is typically added to the ingredients. This starter contains the microbial community needed to establish fermentation. Kimchi does not use a starter culture, but is still able to ferment.
Then where do the fermentation microbes come from?
Phylogenetic analysis based on 16S rRNA sequencing indicates that the kimchi microbiome is dominated by lactic acid bacteria (LAB) of the genus Leuconostoc, Lactobacillus, and Weissella. Kimchi relies on the native microbes of the ingredients. That is, the microbes naturally found on the ingredients. Because of this, there may be wide variations in the taste and texture of the final kimchi product depending on the source of the ingredients. In fact, a research group from Chung-Ang University acquired the same ingredients from different markets and sampled the bacterial communities within each of the ingredients. The group found a wide variability in the same ingredient when it was bought from different markets. Surprisingly, the cabbage was not the primary source of LAB. Instead, LAB was found in high abundance in the garlic samples. For a more detailed account of how initial ingredients affect the final product, head over to Microbial Foods or to the original paper from the research group.
LAB are able to proliferate rapidly due to the anaerobic conditions, low temperature and salt content of the kimchi mixture. As the fermentation progresses, the species composition within the kimchi changes (this change is called ecological succession). Ecological succession in the kimchi can be altered by changing parameters such as salt content and temperature of incubation. Therefore, batches of kimchi containing the exact same starting ingredients may end up producing a slightly different flavor when fermented under 1% salt versus 3% salt.
In studying the microbiome of kimchi (and other fermented foods), we can learn how changes in the bacterial communities over time affect the flavor and texture of our foods. Perhaps one day, we can customize kimchi by adding starter cultures of specific combinations of microbes to produce the desired flavor profiles in the end product.