Can you make ferments with old vegetables?

The ostensible reason why I’m here is to investigate how traditional methods of Chinese fermentation can reduce food waste and save energy. Given this fact, and also the highly fortunate situation that I’ve been given access to an entire food science laboratory to use as I wish, I designed a little experiment that I’ve been working on for the past week.

Basically, what I’m looking to find out, is if you are in the (highly familiar) situation of having some past-their-prime veggies in your fridge—they’re soft, a bit wilted— and are about to chuck them, what if you could ferment them and eat them later instead?

The basic method I’m using to conduct this experiment is relatively simple—it turns out to be a pretty involved process to measure the specific nutritional content of different types of foods— but I think will give results nonetheless. Last week, I bought a da bai cai, which I think is called Napa Cabbage in the US, as well as some fresh ginger, a head of garlic, hot pepper flakes, salt, sugar, vinegar, and Sichuan pepper. I divided the cabbage into four equal parts, and planned to make pao cai (spicy pickles) with them at different time intervals. This way, I could see if the same cabbage’s edibility changes after making different batches of pao cai with it at various stages of decay.

The recipe I used was an amalgam of an experiment outlined in an old Chinese fermentation lab handbook that the professor I’m working with gave me, along with this recipe, which I thought was well-researched and thorough.

I used the first quarter to make a batch of pao cai on May 20th, and the second (which I left out overnight without refrigerating) on May 21st. According to my Chinese grandmother friend, the pao cai should be left out for three days fermenting at room temperature, and then put in the refrigerator and eaten within three days. It can stay in the refrigerator for longer, but after a while, it begins to become somewhat mushy.

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From what I’ve been able to find, no one in the literature has done an experiment like this before. However, I was able to find many studies about the loss of nutrients in vegetables over time, as well as the effects of freezing and drying. The loss of specific nutrients largely depends on the type of vegetable you’re studying. For example, in a 1987 study I read, more than half of the ascorbic acid in leaf lettuce was lost after 6 days of refrigeration, whereas only a quarter was lost in refrigerated broccoli. In another Chinese study I read, found by one of the PhD students in Professor Shen’s lab, the total nutritional content of red radish and white lotus root decreased to a much lesser degree after fermentation in salt water than carrots, lettuce, and broccoli.

Although it is natural for the levels of various vitamins present in fresh vegetables to decay after harvesting (even in the refrigerator), it is also the case that fermentation can make certain vitamins more bio-available, as it is a sort of “pre-digestion” process.

While my methods are not very scientific (although I have been using the same weight and volume of materials for each batch, as well as regularly testing the pH), I am relying mostly on look, texture, and taste for this experiment. Today everyone in the lab tried my first batch of pao cai, and seemed to like it, although I did hear quite a few people say I had made it too spicy.

Today, five days after making the first batch, I began the third batch, the cabbage for which has been sitting in the refrigerator all week. Next Monday, I plan to make my final batch, the last test. I think the results of this experiment could be particularly applicable to city-dwellers, who have less access to composting areas, or for foodies in general. I’m hoping that the results of the final test will still be edible— wouldn’t it be better to have a salty, sour condiment to a sandwich, soup, or salad, rather than a pile of lettuce leaves rotting in the trash?

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the first batch
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