Why does yeast make dough rise

Jr. scientist A often asks why we add different ingredients when we cook and one of the common ingredients we use (since we make a lot of pizzas) is yeast. I decided a while back to try to give a better answer than my standard, "yeast makes dough get bigger" response. I knew that there was carbon dioxide being released that formed little pockets in the dough, thus expanding it, so I thought we could do an experiment where we use yeast to blow up a balloon. Originally I put some yeast and water in a bottle and covered the mouth with a balloon. We checked on our experiment the next morning to find a still deflated balloon. I tabled the experiment for a while and was poking around online and found I was missing a key ingredient - sugar. We re-did the experiment with two bottles. The smaller bottle had yeast and water and the bigger one had yeast, water, and sugar. By the next morning the bottle with sugar had a nicely bulbous balloon sitting on top of it. Thanks to some laziness, we discovered that the bottle without sugar did eventually make enough carbon dioxide to partially inflate the balloon, but it took a few days to happen.

Colorful cauliflower

We had some extra cauliflower so we decided to do a capillary action experiment. We filled a small glass with water and food coloring and suspended some cauliflower over it with the stem in the water. We let it sit out overnight and in the morning Jr. scientist A came bounding over to me shouting "the experiment worked!" Clearly a winner.

Separating colors

This experiment came from friend-of-the-lab Sandy. The goal of the experiment was to show that black is made from a mixture of colors. We put a long strip of paper in a bottle so that the paper went from the bottom of the bottle, up and out the top, and down to the table top. We filled the bottle part way with water and made a thick black line on the paper above the water level using a permanent marker. By the morning, our thick black line had turned into a smearing of colors. Although Jr scientist A would clearly have liked the black to separate before our eyes, the experiment clearly sparked his imagination and he's now asking to see what other colors are made of.

Stalagmites and stalactites, take 3

Never willing to admit defeat, we've made another try at making stalagmites and stalactites. We noticed that the area around our crystal experiments was covered with crystals. It seems that the salt water evaporated in the hot sun, but was too heavy to stay in the air and condensed out. We decided to take advantage of this to try to grow stalactites. We put a mesh (a cut-out from a screen door) on top of the jar for our latest experiment, hoping it would catch the escaping evaporated salt water. We poured our crystal making materials into the jar while it was covered by the screen so some of the liquid would stay on the screen and start a layer of crystals for the rest to hang on to. We weren't able to grow stalactites with this technique, but we got an unexpected but happy result. The evaporated salt water seemed to get trapped inside the jar so we ended up with one big thick crystal that covered the bottom of the jar. Pretty cool. I want to try this in a disposable cup next time so we can easily get the crystal out to play with. It looks like we'll finally have crystals that aren't to delicate to handle.

Growing corn, a summary

Our corn growing experiment is finally at an end. We went from popcorn kernel to ears of corn. I have to admit I didn't imagine that we would actually pull this off. We knew almost nothing when we started - even mistaking the flowering part of the corn stalk for the corn - but with a lot of luck (and some research along the way), we actually grew corn. Jr. scientist A loved watching his corn grow and get taller than him. He was so excited when we got to pick the first ear of corn - he wanted to tell everyone! Now what can we try to grow next year?

From seedling to plant

We planted our seedlings that we grew from popcorn kernels. We had a fun time filling biodegradable pots with soil, sticking in the seedlings, and planting the pots. I wasn't really sure if they'd survive the transplant, but we dutifully watered them every day. Within a few days we started seeing little plants poking out of the soil. Since then they've just kept growing and growing. It's neat to see what our little popcorn kernels are turning into. We're now working on trying our hand at baby carrots.

From seed to seedling

After a few fun trips to our local plant nursery, I thought it would be neat to show jr. scientist A. how a seed turns into a plant. We took a plastic container and lined the inside wall with a damp paper towel. Then we stuck a few popcorn kernels between the paper towel and the wall of the container. With dutiful watering to make sure the towel stayed damp and a nice sunny windowsill, we started to see some sprouting in a few days. A few days after that there were little purple roots climbing downwards and little greet shoots climbing upwards - how do they know how to do that! Tomorrow we're planning on transplanting our seedlings to a dirt pot to let them grow bigger.

Raising a butterfly

Our local kids museum has an annual adopt-a-caterpillar event. You get a very tiny caterpillar to take home in a small container. Over the course of a couple weeks you get to see it get bigger and bigger. Then, as jr. scientist A liked to recite, it would "build a cocoon, stay inside for two weeks, push its way out and be a beautiful butterfly!" (the last two words were always said loudly with arms up in the air). It was a really neat experience, although jr. scientist A was sad when we released our little friend into the wild.

Meeting in the middle

Time for more fun with food coloring. We had previously used two colors to see whether salt water was slower to diffuse than fresh water. This time we repeated the experiment with two containers of differently colored fresh water. To our surprise, although the colors eventually seemed to meet in the middle, the red took days longer than the yellow color. It seems that whatever makes the different colors causes them to diffuse at different rates. We'll have to play around with that some more.

Crystal growing mediums

Since our previous attempts at growing stalactites have yet to yield anything remotely resembling a stalactite, we decided to take a step back and do some pilot experiments. There seems to be a few problems that potentially need to be addressed. 1) How do you get a nice slow drip for the salt water so that the crystals can grow over time? 2) What type of materials will the stalactites grow best on? 3) How do you refill your salt water solution without dissolving the already formed (water soluble) crystals (i.e., whatever makes the slow drip has to either never release the solution faster than a drip or be detachable)? I'm sure there's a few more we'll run into.

We've previously made some good progress on the first problem. We decided to attack the second problem by trying to grow crystals on different materials. We made our crystal solution, dissolving as much salt as possible in super heated water. This time we used table salt - nice and safe to handle and eat (good for a toddler hands-on experiment, that is, once the water has cooled). We poured the crystal solution over cardboard, paper, wood (a popsicle stick), and wool yarn. We set the materials in a window for a couple days and then checked on our results. The crystals grew everywhere (including on the plastic container the materials were in), but they just looked like big grains of salt on most of the materials. The one that stood out was the yarn (shown above, enlarged). There it seemed to form large crystal structures that looked like they'd be ideal for the beginnings of stalactites. I think we found our crystal growing medium!

Water race

To try to show that, even though water looks the same after you dissolve salt in it, it's changed, we decided to compare the speed of diffusion for salt water and fresh water. We filled one bottle with fresh water, dyed green, and a second bottle with water with Epsom salt dissolved into it, dyed red. Then we rolled up a paper towel and put an end in each bottle. The green fresh water started climbing the paper towel. At first it looked like the red salt water was just sitting there, but we checked and the un-dyed paper towel coming from the red was wet, while the paper towel from the fresh water was only wet where it was green. Eventually the red color started moving along the towel. It looks like the salt slowed the diffusion of the color, but not the diffusion of all the water.

Making water run upstream

We decided to try to make water run upstream, so to speak, using diffusion. We filled a bottle with colored water. Then we took a long piece of paper towel, rolled it up, and used string to keep it rolled up. We put one end of the paper towel in the water-filled bottle and the other end in an empty bottle that we put on a raised platform. Nearly instantly the colored water started creeping up the paper towel. We quickly learned that a paper towel saturated with water is much heavier than a dry paper towel and we had to add supports to hold the paper towel up. Throughout the evening we watched its slow progress. We checked on it in the morning and, to our surprise, the water hadn't made it all the way to the other bottle. Instead, it stopped part-way up, leaving a dark ring of color, followed by dry paper towel. I guess diffusion will only go so far.

Stalagmites and stalactites, take 2

Our second attempt at making stalagmites and stalactites with salt crystals. This time we used a paper towel to connect the two jars filled with Epsom salt dissolved in water. The liquid did slowly travel up and across the paper towel, making the paper towel rigid, and we got some crystals forming below the paper towel, but nothing that looked like stalagmites or stalactites. We'll have to keep trying.

Making paper

For this experiment we turned paper into... paper. We started with some old newspaper and magazine pages and tore it into shreds (Jr. scientist A. is so good at doing that with paper he's not supposed to tear, but seemed unwilling to do it when he had permission!). We put the paper and some hot water in a blender, let it sit for 20 minutes, and then blended it into a watery mixture. We poured the mixture over a silk screen that was placed over a bin lined with a garbage bag. We then added leaves and a pressed flower we had collected on walks and pressed out some of the water. We let it sit in the sun, periodically pressing out more water. We eventually learned to put wax paper on top of the mixture before we pressed out the water after we kept pulling off parts of the "paper." After a day, it had dried and we carefully peeled it off the screen. We were left with (somewhat delicate) paper that had some of the leaf patterns pushed into the back side. A fun, albeit slow project.

Sun bleaching in the rainy season

We did some more sun bleaching - this time making sure everything was firmly attached to prevent the cats from interfering. It ended up raining and raining and raining for days in a row, making it take more days than usual. In the end it turned out pretty well. Jr. scientist A. wanted me to cut out the rectangle to carry around and then was surprised that, without the surrounding bleached out paper, it just looked like an ordinary sheet of construction paper.

Growing crystals

We tried to make crystals by dissolving Epsom salt in water. We heated water up in the microwave (so we could dissolve the salt at the table in plain view). After we dissolved as much salt as we could (with some undissolved salt sitting at the bottom of the cup) we microwaved it again. This dissolved the remaining salt and let us mix more in. We repeated this a couple times, added food coloring, and poured a shallow layer of the solution into a tupperware container. After letting it sit a couple days so the water could evaporate, we were left with some rather unimpressive crystals. It was essentially a somewhat sparkly layer of material. We'll have to work on making better looking crystals.