Cranberry Harvest

Our Jersey Shore bungalow is near the cranberry bogs in Double Trouble State Park in the Pine Barrens of New Jersey. Luckily this year, we–me, Linda, and Sophie, my three-year-old granddaughter– managed to get there from NYC in time to watch the wet, or water harvest; an event I’ve been curious about, especially after writing my forthcoming book Thanksgiving: The True Story. The first two pictures (left to right) show a cranberry bog with ripe berries (cranberries grow on a dwarf evergreen vine in a peat or sandy bog), and two specialized harvesters that knock the berries off the vine. In that picture, the first driver has lifted up the bar that has 9 metal circle because he’s about to turn around (see next picture). The other driver still has the bar down and the circles are rotating and knocking the cranberries off the vine (note the water in the bog splashing up). The man wearing the waders directs the drivers and walks in front of them to make sure they don’t hit a rock or other obstacle.
“Hey,” I shouted to get his attention. “What do you call those machines?”
“Knockers,” he shouted back. “Also pickers, I call them pickers.”
“What do most people call them?”
“Ask him,” he said gesturing to a man standing a bit behind me. Jose has been doing this for fifty years.”
Turning to look as Jose, I asked, “What do you call them?”
The next two pictures are of the bog after it has been flooded with 6″ to 8″ of water. Since cranberries float, the workers corral them by encircle them with a very long piece of black, flexible material about 8″ wide that floats. We could see two workers standing in the corral using a type of push-broom to move the cranberries around but couldn’t figure out why. Walking to the side of the truck, we found a man on a ladder who was watching the cranberries fill up the truck.
“Hi,” I called out, “We have a question.” I didn’t expect him to climb down, but he did and cheerfully explained that there is a tub just below the surface of the water with a suction hose that sucks the cranberries up to a platform on the back of a truck. The men in the water are moving the cranberries toward the tub. Periodically one of the men walks over and tightens the black strip encircling the cranberries, thus making the corral smaller; a task, we all agreed, looks like hard work!
The last picture shows the workers standing on the platform. They remove pieces of vine and use a type of push broom to move the cranberries onto a conveyer belt that dumps them into the back of the truck that will go to the receiving station in Chatsworth, NJ. That is where the cranberries get processed into juice and cranberry sauce. (Cranberries that are sold whole are gathered by a “dry harvesting” method by which mechanized machines “pick” the cranberries). As we were leaving, a woman wearing a “Piney Power” T-shirt hailed us to warn us about chiggers (happily no problems for us). Ever the journalist, I asked her about her t-shirt, etc. and discovered she has a cool website ( with lots of material about the Pine Barrens, including information about cranberries.

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3 Responses to Cranberry Harvest

  1. Susan says:

    I just had a delightful conversation with Penny about this blog entry on cranberry harvests, which got us to talking about science education and teaching. After our conversation I began thinking again about the popular slogan “science is everywhere.” In fact, “science” is not everywhere. Science is a human construct, an enterprise, a way of viewing the world. It is not an object. So, what should we say to kids if we want to stop saying, “science is everywhere”? I propose we start by explaining that if we want to understand the world around us, then opportunities for thinking scientifically are everywhere we are and they are enhanced by being around others who enjoy thinking and talking scientifically about their surroundings. For some children, the opportunity to work with others can only be found in school, for others their home and school lives are rich with interactions that support the development of their scientific reasoning strategies. Penny’s non-fiction moments reflect her curiosity about people and nature, but more importantly for her students (new and future teachers) they provide a structure to being curious that they can use to engage students in learning science, history, mathematics, art, music, etc.

    When I read Penny’s blog entry on cranberries to my husband, Moshe, he asked, “Why do cranberries float?” (If you know my husband, you also know that he probably has an answer to the question, or at least a thought). He claimed not to know the answer and he tried to find out with a quick Google search and in the process read that cranberries are pollinated by domesticated honeybees and are related to blueberries, which I think Penny had already told us. We agreed that there must be some evolutionary explanation and when I pressed him to provide a conjecture for why cranberries float, he thinks it might be for seed dispersal (e.g., cranberries can float down a stream to a new location where they germinate) and I think I have to agree. I don’t remember seeing a seed in the last cranberry I ate. Hmmm. It turns out that the cranberries are tricky to propagate and the seeds need a freezing period before they can germinate from overripe fruits. All sorts of environmental requirements like this one have been noted by botanists who study germination. Plants are very cool, eh?

    “Complete manual for the cultivation of the cranberry: With a description of the best varieties” by B. Eastwood (1859).,M1

    Sue Kirch

  2. Penny Colman says:

    Hey, Sue and Moshe, my question for you is: HOW do cranberries float?
    By the way, Sue and Moshe are research scientists. Sue was my colleague at Queens College, the City University of New York. Currently she is a science educator on the faculty at the Steinhardt School of Education at New York University.

  3. Susan says:

    This is a great question, Penny, and one that teachers and students invest a lot of time in understanding. For physicists it is a fundamental principle that was first described by the mathematician, physicist and engineer Archimedes of Syracuse in about 250 BCE!

    When you asked how cranberries float I realized that this is a really popular school activity – to throw stuff in water and see what sinks or floats. There are probably hundreds of versions of this activity available online (for an example see: So, may I change your question to how does anything float in water? Or what determines whether something (liquid or solid) floats or sinks in water?

    For example, we could ask:

    How come massive ships float but tiny pennies sink?

    How come logs float but rocks sink?

    How come a cranberry floats, but an equal sized lead fishing line weight or a steel ball bearing sinks?

    I am sure you see where I am going at this point. You mentioned that you and Sophie cut or broke open a cranberry that day and noticed that it looked like Styrofoam (or a sponge? I can’t remember) inside. I think you said it looked like it had lots of tiny pockets or bubbles of air inside. Well, I bet if you made a thin slice of the berry and a thin slice of a Styrofoam packing peanut and looked at them with a high magnification hand lens or microscope you might be able to see that they look similar – like honeycomb with a lot of structure that allows the berry (and the foam) to trap air, but also store plenty of nutrients for the seed(s) inside to use for germination (I am just guessing here because I haven’t looked myself or seen a photo of it – Sophie needs to check on this for us).

    Anyway, the structure of the berry and the structure of water are what allow the berry to float in water. It turns out that the berry is not as “dense” as the steel ball bearing of the same size. This is, it is made up of combinations of atoms that have lower molecular weights (masses) than the combination of atoms that make up a steel ball bearing. These atoms combine to form molecules (sugar, carbohydrates, proteins) that take up a certain amount of space (volume). The fruit develops its particular shape and size based on instructions encoded in the plant’s DNA. In the case of the cranberry the plant doesn’t pack too many goodies into the sphere. If the plant made a fruit that did not have air spaces, but filled the air spaces with more nutrients and maintained its size (volume) it might make berries that sank! I am not sure if anyone has discovered or accidentally made a cultivar of cranberries where the fruits sank. It would be interesting to see how the DNA of those plants differed from the DNA of the plant that made floating fruits. Of course, the plant also makes a watertight outer coating that protects the spongy inner core of carbohydrate and air from filling up with water. I wonder if Sophie pierces the outer coating whether she will see the berry eventually sink.

    I really have to go now, but perhaps you remember that I mentioned that the structure of the water is also very important? We have to consider the density of water, too. Water is an object with enough density (mass per volume) to push back on the berry, but not dense enough to push back on the steel ball bearing and keep it from sinking. So the bearing is able to displace a lot of water (push it out of the way) and sinks until it does reach something that is denser than it (the bowl, table, or Earth). The berry only displaces a little bit of water (that’s why it looks like some of the berry is under water and some is above the water). So, if Sophie changed the composition of the water by adding lots of salt or sugar and made the water denser what would happen to the berry? What would happen to the steel ball bearing? What if she could stretch the steel ball bearing into the shape of a thin-hulled rowboat or a balloon? At what point will they float on water? Answering these questions will lead her to learn about buoyancy – which really explains how things float (and why they sink). There are lots of resources on this too:

    You know I learned this stuff in my physic classes, but it wasn’t until I had to teach it to others that I really understood it. It is like learning a foreign language, the earlier you learn it the easier it is to remember! I learned it fairly late (college, grad school, now), which means, sometimes, I have to do a lot of work to keep it all straight. I have just referred to concepts of density, mass, matter, genetics, molecular structure, and buoyancy in these few paragraphs. I don’t expect anyone to really understand these concepts just by reading what I have written here, but I do hope to show that learning how things work requires a lot of reading, questioning, and trying things out (through thought experiments and real experiments) and it is a lot of fun!

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