Season 3, Episode 5: The Science of Fermentation

Conner: (00:01)
Welcome to Kiddos in the Kitchen, a podcast hosted by my mom.

Phoebe von Reis: (00:18)
Every time I step into the kitchen, I think everything feels a little bit like a science experiment, because cooking with heat and fire, you're watching the molecular structure of things change. Maybe they melt, or maybe they get crunchy, and I think it's fascinating.

Stephanie: (00:39)
Phoebe von Reis has worked in restaurants for much of her life. She also grew up learning from parents who cooked from scratch. Today, as a mom to three teenagers, Phoebe focuses on healthy, nourishing foods. And for her family, making fermented foods are a big part of that. Welcome to Kiddos in the Kitchen, a podcast about helping busy adults find the inspiration and information they need to teach the kids in their lives how to cook. I'm your host, Stephanie Conner. And today, we're talking about fermentation and how this process can make for a fun kitchen/science project with our kids.

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Stephanie: (02:00)
Phoebe was introduced to fermentation nearly 15 years ago by her younger sister, who spent time traveling in Europe and learning about this technique. So let's start with the basics: what exactly is fermentation?

Phoebe von Reis: (02:17)
Lots of things that we eat are fermented, like chocolate for example, which I love to eat. A lot of adults like to drink wine, of course, which is fermented for quite a while, the byproduct of that is alcohol. When foods are fermented, they go through a process where the structure is being broken down. So it happens in an anaerobic environment, which just means there's no oxygen. And what happens is wild yeasts and bacteria that are good bacteria, that are in the air, will settle on a piece of cabbage, for example, or carrots when they're growing and the yeast start to eat up the sugars that are naturally in the vegetables or fruits. And, they produce lactic acid or lactobacilli, and that can give off carbon dioxide as bubbles. And when that gets released, say in cabbage, it can turn things sour; a lot of people call it pickling.

Phoebe von Reis: (03:23)
And what happened in kind of around the 1940s and ‘50s, when all of our lives started getting a lot busier, people started pickling with vinegar. But the old way, the ancient way to pickle is just with salt. So when you put salt with your vegetables and it's all submerged under the brine, you mix the salt with water, or some of the vegetables can release their own juices, then it turns it sour. And lots of interesting things happen at that point. For example, cabbage is already something that has a lot of vitamin C in it, but once it's fermented, not only does it have some live bacteria that are very good for our gut biome, it also doubles the amount of vitamin C; and then the longer a ferment goes, more and more of these different bacteria, which a lot of people call probiotics now. At around the six-week mark, if you let your sauerkraut go all the way for six weeks, that's when B vitamins start coming out.

Stephanie: (04:28)
So you mentioned cabbage and sauerkraut, which I think is maybe one of the few examples that most of us could name, but you also were referencing other vegetables. So, how do you know if a food is fermentable or a good to ferment?

Phoebe von Reis: (04:42)
Yes.

Stephanie: (04:43)
I guess, everything could be, I don't know.

Phoebe von Reis: (04:44)
Everything could be, it kind of depends on what you like. I kind of think you could ferment any vegetable, but some things I don't think personally taste great when they're fermented, like broccoli. I have never tried fermenting broccoli.

Stephanie: (05:01)
Broccoli, she suspects, wouldn't have the texture she likes in fermented veggies. She prefers them to be crunchy like a pickle, but this discussion made me think, could we turn fermentation into something of a kitchen-based science project with kids?

Phoebe von Reis: (05:19)
Every time I step into the kitchen, I think everything feels a little bit like a science experiment, because cooking with heat and fire, you're watching the molecular structure of things change, or maybe they melt or maybe they get crunchy, and I think it's fascinating. And with fermenting, it's a similar thing. There's this biochemical process happening that we don't necessarily get to see. Sometimes you can see bubbles forming, sometimes when you're making sauerkraut, you can hear a little blurp that happens in the jar, because that air is getting released. I think it's great when you approach a lot of things in the kitchen as a science experiment. And what's fun is that, things don't always turn out the same way twice. It's fun to try to figure out maybe why that happens. And with fermenting, there are so many different factors that can come into different outcomes, such as temperature, or I think people's ferments taste different, even just from what their own molecular biology is like, what lives on your hands or where you live.

Phoebe von Reis: (06:37)
There's going to be different airborne yeasts. I see it as not only a science, but also kind of as an art. You might want to ferment something and you know you love the taste of cumin, or you love the taste of oregano, so you want to add that into your ferment and it becomes your own flavor profile. You can really sort of create a lot of different taste experiments with whatever you decide to add to the vegetables you're fermenting. You can kind of wing it, you can be like, "Okay, I think this is the amount of salt I'm going to add and I'm going to taste to see if it tastes right." Or you can get very specific and you can weigh your salt, and weigh your cabbage and try to get the salinity to be within a certain amount. You want it to be about 1.5%.

Stephanie: (07:30)
I'm going to pause here to explain. That 1.5% she's mentioning is the ratio of salt to food, so for every 100 grams of cabbage, you'd use 1.5 grams of salt.

Phoebe von Reis: (07:45)
What's interesting too, though, is that you can get away using less salt in the summertime and a little more salt in winter, just because that high temperatures will speed up fermentation and lower temperatures, it'll take longer for your ferment to go through the stages and get to that sour stage that you like.

Stephanie: (08:06)
Next, I asked Phoebe to walk us through a straightforward fermentation project that we can do with our kiddos.

Phoebe von Reis: (08:13)
I think the simplest thing to do, which is really fun to do, that any kid enjoys doing is making a very simple batch of sauerkraut. And all you really need is a cabbage and some salt, and it's best to use a natural salt, like a sea salt, or kosher salt is okay, but iodine in regular table salt can prohibit the fermentation to take place. And then, you need a vessel. I like having a crock specifically made for making sauerkraut, but a jar works great, a jar with a lid. But even if you didn't have a jar, you could try making it in a bowl and have a plate that kind of fits the top with the bowl, because everything at the end needs to be underneath this liquid. Otherwise, you can have things happen like mold and you don't want to have moldy sauerkraut, that's no fun.

Stephanie: (09:07)
No. So let me pause to ask, does the type of cabbage matter?

Phoebe von Reis: (09:13)
No, not really. Purple cabbage is really fun because then you get this, like, fun color, brine liquid, and it turns your hands purple. But, it has a slightly different flavor. I think it tastes a little bit sweeter than the green cabbage. If you know you love things that are spicy, there's a grape ferment called kimchi, which is a Korean ferment. It's usually used to different kind of cabbage, which is the Napa cabbage, but it doesn't stay as crunchy. So if you like crunchy, I would go with a regular green or purple cabbage. What you would do is you would dice up your cabbage into strips, so you're going to cut it in quarters and you could leave the core in if you want to, but I usually take that thick core at the bottom out. But you also need to remember before you dice it, to save one or two leaves, full cabbage leaves because you're going to need those at the end.

Phoebe von Reis: (10:08)
And, you dice up your cabbage into thin strips and put it into a bowl. Cabbage comes in different sizes. You can weigh your cabbage if you want. So if you had a one-and-a-half-pound cabbage, you would want to have about a tablespoon of salt. You're going to sprinkle that salt over the top of this cabbage and start massaging it and that's where it gets fun. Make sure you wash your hands first. I have some friends who don't like massaging, because they think it's kind of tiring and they'll use a wooden mallet or something to kind of crush it up that way. But, I like to massage it and I think it's fun to get your hands in there. It's good for your muscles. It'll take a good five minutes, it kind of depends on the cabbage.

Phoebe von Reis: (10:57)
Start working that salt into the slices of cabbage and what happens is, all this liquid starts to come out, this cabbage juice. You want to keep massaging until once you press down on the cabbage with your hands flat in the bowl, that the juices from the cabbage come up over your fingers. You want to have about a good inch or inch and a half of liquid come out of that cabbage, so that once you pack it into a jar, everything is submerged, because that's how the fermentation is really going to get going without any oxygen. So those vegetables, there's a little phrase we say, under the brine, everything's fine. You want to make sure that all the cabbage can be underneath the liquid. And when you're fermenting something like, say, carrots, which you can't massage any juice out of, you just make your own brine. You mix together water and salt.

Phoebe von Reis: (11:54)
Use about two teaspoons of salt for every cup of water, mix it up and pour it over the carrots in the jar. And then, you still want to make sure that the carrots aren't going to float, so you could use any kind of weight that you have, and you can get a little creative with this. They make fermentation weights that are made of glass that you can buy. But sometimes, I'll just find a jar that's smaller than the jar I'm using and I'll push that down with a cabbage leaf under it, so that the little pieces of cabbage don't float up. Or if you decide you wanted to put some seeds in there, try to keep them all underneath the water. Because anything that's floating on the top can invite oxygen in and then you can get some spores of things that you don't want in there, that could make the batch get a little bit moldy, but that doesn't happen very often.

Phoebe von Reis: (12:45)
I've only had in the last 15 years, maybe one or two batches of sauerkraut that seemed off and you can tell just by smelling it or looking at it, if it has something furry on it, that it doesn't smell right. Use your scientific nose to see how it smells.

Stephanie: (13:02)
If I see fur, that batch is going out.

Phoebe von Reis: (13:05)
Exactly, you don't want to eat the furry mold. And then you put your lid on your jar, you have it underneath a cabbage leaf, all those pieces of cabbage that you massaged. And then you could put a small glass, like a little shot glass or something to hold it down. Or like I said, another jar, or if you have a river stone that you found that maybe you run through the dishwasher first or pour boiling water over it to sanitize it. Sometimes the cabbage leaf itself is heavy enough to tuck down, and push everything down, and it will stay that way if you have enough brine over the top of that cabbage leaf.

Phoebe von Reis: (13:42)
I've also tried using the top of a butternut squash. If you have any butternut squash, you could chop off the very top of it and press it down, and it's kind of heavy enough to hold everything under the liquid. And then, you close that off with a lid and you want to leave some space at the top, because as it ferments, it expands a little bit. You remember that that carbon dioxide comes off and it can make it bubble up. And it will also slowly, as it's fermenting over the next three weeks, four weeks, five weeks, six weeks, however much patience you have, it will expand and more liquid will start to come off, too. Sometimes I'll put a plate underneath my jar and I'll tuck it somewhere where it's out of direct sunlight.

Phoebe von Reis: (14:31)
I usually will put it maybe in a cupboard, you can just kind of put it in the shady part of your kitchen, so you can watch it sometimes too. And then it's just a matter of letting all of those microorganisms do what they do best, which is start turning those vegetables into a delicious, crunchy probiotic, vitamin-rich treat. And, it's so yummy on top of pizza. It's really yummy with potatoes and eggs. It's really yummy on top of a taco. It's delicious just to have a bite of on a spoon. I know some people when they have that afternoon sweet craving, instead of going for a cookie, they'll just open their jar of sauerkraut and take a bite and their sweet cravings go away.

Stephanie: (15:17)
You mentioned leaving your fermentation going for a few weeks, does the fermentation time affect the flavor at all? If I have part of my batch that I pull out at three weeks and part of my batch that I try at six weeks, will I notice a difference, you think?

Phoebe von Reis: (15:33)
That's a good question. I like to let it go for at least three weeks. I think that's a great time to go for it at the beginning. I think it's usually a little bit crunchier. You can soften kind of the longer it ferments. And then, once you've gotten to at least that three-week mark, then you want to put it in the refrigerator, and then it will keep for a long time. My sister has the saying, "It doesn't go bad, it goes good." But it keeps sort of slowly fermenting a little bit in the refrigerator.

Phoebe von Reis: (16:00)
Refrigeration really halts all of those processes a lot, but those good bugs that are in there, they never really go bad. It's a great project and I think it's fun too, that we have to be patient, that we have to wait for the results. And it's longer than just half an hour in the oven for crackers, or cookies, or a loaf of bread or something like that. It's fun for little kids to understand that it’s sort of a long time to get this precious food that's so good for us and makes things taste so good too.

Stephanie: (16:34)
Another area of exploration is letting kids season their fermentation with different herbs, spices and citrus. Phoebe likes adding in some lemon, for example, she even ferments whole lemons to use in her cooking later. She also suggests experimenting with seasonal herbs, dill, caraway seeds, leeks, onions, anything your heart desires. And now, it's time for Kitchen Questions. We had one more question for Phoebe about one of her favorite fermentations.

Kids: (17:07)
It's time for Kitchen Questions, I have a question. What would happen if you put a little bit of the wrong ingredient inside a cookie? Why are cupcakes squishy? How often do you burn things on accident? Do you like cake? What is the difference between baking and roasting? What is your favorite recipe?

Conner: (17:37)
What is the secret to a perfect sourdough?

Phoebe von Reis: (17:42)
Ooh, practice, practice, practice. I think the secret to really perfect sourdough is having a hot oven. So you need your oven to go up as high as it will, like 550 degrees. A lot of people will spray it with water, so you kind of want sort of a steam thing to happen. But if you have a Dutch oven pot, you can keep the lid on until maybe the last 15 or 10 minutes of when you're baking, you could take that lid off and that'll get that nice crusty, crunchy edge to a nice loaf of sourdough bread.

Phoebe von Reis: (18:17)
I like to feed a sourdough starter with some rye flour, it helps it ferment a little bit faster. I think it gives a little more of a sour taste. I like my sourdough really sour. Making bread is definitely an art form.

Stephanie: (18:36)
Thank you to Phoebe von Reis for joining me today, and giving us a fun way to explore food and science. You can follow Phoebe at phoebecornelia.co on Instagram, and I'll share a few links, including one to one of Phoebe's favorite books on fermentation in the show notes at kiddosinthekitchen.com.

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Stephanie: (19:33)
For me, time in the kitchen is about time spent together. It's also an opportunity to talk about family heritage and world cultures, it's time to talk about hopes and dreams or just what happened at school today. But kitchen activities also present awesome opportunities for education, experimentation and fun as well. What happens when you mix baking soda and vinegar? What happens when you don't let the butter come to room temperature? What happens when you omit certain ingredients or add in others? I've never fermented veggies, but after talking with Phoebe, I'm certainly intrigued, and I'm excited about the opportunity to ferment our own pickles and jalapeños as a start.

Stephanie: (20:29)
And then I guess, we'll have to try some sauerkraut, and play with flavors and techniques. Sometimes we focus on what we're making, whether it's a family recipe we're passing down or simply trying to get dinner on the table, but kitchen time can be about the process too. Even when our fruit soda, another type of fermentation, didn't work out last summer, there were lessons to be learned. So as you think about your next kitchen activity, remember that it doesn't always matter where you end up, there are lessons to be learned and fun to be had along the way. Thanks for joining me for Kiddos in the Kitchen. I'm your host, Stephanie Conner, with a reminder from my son.

Conner: (21:23)
If you like my mom's podcast as much as I do, you can subscribe on Apple Podcast, Google Podcast, Stitcher, Spotify, or wherever you get your podcast.

Stephanie: (21:41)
That's right, Conner, you can also view the show notes, subscribe to our newsletter and check out all of our other content at kiddosinthekitchen.com, we’re Kiddos Cook on Facebook, Instagram and Twitter. And I'll be back next month with another fresh episode. Until then, I encourage you to get your kiddos in the kitchen.