The ancient Egyptians were excellent engineers, especially considering the paucity of tools and materials they had available. But with their human- and animal-powered machines, they invented a host of real and useful technologies.

Building a Replica of the First Food Processor

The ancient ruins of the Egyptian city of Memphis stretch for nearly 20 miles along the banks of the Nile River. The oldest artifacts date back five millennia to the “Old Kingdom,” the period during which the earliest known pyramids were built. At the spot called Saqqara on the river’s western shore is a particularly spectacular concentration of temples, tributes, and tombs—achievements credited to the laborers who worked more than 4,000 years ago for the pharaohs of the third, fourth, and fifth dynasties.

Among those pyramids and sphinxes lies a square, bench-like tomb called the mastaba of Ptah-Hotep. Ptah-Hotep was ancient Egypt’s prime vizier and a close confident of Djedkara, the reigning pharaoh. The size and grandiosity of Ptah-Hotep’s final resting place show that he was a BMON (Big Man on the Nile) and a person of great wealth and influence.

Many scholars believe that Ptah-Hotep’s book, called The Maxims of Ptah-Hotep, is among the oldest texts in the world—it was written more than 4,000 years ago. It is a collection of maxims that he dictated to either his scribe or his grandson around the 25th century BCE. It seems to have been quite popular in its day, due, no doubt, to the sagacity of the advice it provides. The oldest known copy still exists in the collection of the National Library of France in Paris.

One who is serious all day will never have a good time, while one who is frivolous all day will never establish a household.

—Maxim 11 from The Maxims of Ptah-Hotep

It looks like Ptah-Hotep was able to establish a successful balance between seriousness and frivolity because he was interred in one of the largest and most impressive tombs in all of ancient Egypt. Not only that, but the carvings on the walls show the life of man who not only worked hard, but played hard as well.

The scenes on the walls of Ptah-Hotep’s tomb that particularly interest archeologists include carvings that illustrate early boat building, cloth weaving, and fish drying. From those you can see he was serious about making Egypt prosper through industry, and from them, we modern folk can get some idea of how the people of those ancient times worked and lived.

But there are also scenes that show Ptah-Hotep’s lighter side. Apparently the man enjoyed hanging out with friends and enjoying a nice glass of wine with his meals. How do we know this? By looking at the detailed illustrations on his tomb. There’s one in particular (see Figure 2-1) that depicts people drinking wine, but it also shows perhaps the oldest piece of wine-making equipment ever made: the Egyptian bag press.

The wall hieroglyphics show that some clever Egyptian thinker, perhaps even Ptah-Hotep himself, discovered how juice could be efficiently extracted from grapes by wrapping them in a linen bag and then twisting the ends of the bag. Like wringing water from a towel, exerting great torsional forces on both ends of the bag applies enormous pressure to whatever is inside. The press wrings out more juice than would be possible by other methods, including smashing grapes with mallets and feet and then collecting the liquid.

Modern archeologists refer to the operation of bag presses as “wringing the cloth.” Images of the process appear frequently in hieroglyphs found throughout Egypt. In the detailed version of the hieroglyph shown in Figure 2-2, five men working together use a linen bag and poles to extract juice from grapes. Two men twist each stick in opposite directions while a fifth has the rather unenviable job of using his body to separate the two ends as the contracting motion of the twisting bag draws them together.

Three hundred years later, an improved version of the bag press appears in the hieroglyphic record. The ends of the bag are placed through holes in large wooden standoffs and the twist is applied at the points outside the frame, making the process easier and more efficient. You might wonder why it took the Egyptians so long to come up with the idea of a simple frame to hold the bag ends apart, but perhaps the pace of technology was slower back then.

Building an Ancient Egyptian Bag Press

Making the bag press is fun and, perhaps after a fashion, useful. But the main reason to build one is that when you do, you’ll get a better understanding of the way modern science and history evolved from humble beginnings.

Part 1: Preparing the Bag

Begin by laundering the linen cloth. Then, using a sewing machine or by hand using very fine stitching and strong thread, follow these steps:

1. Fold the linen in half along the long axis.
2. Next, fold one short end over twice and stitch a hem.
3. Stitch a seam along the long edge (see Figure 2-3).

   

4. Turn the bag inside out so the raw edges of the long seam are inside the bag.
5. Fold over the end you hemmed in step 2 and sew a pocket large enough to accommodate the diameter of the turning rods, leaving the top and bottom open for the rod. Leave the other end of the bag open (see Figure 2-4).

   

Part 2: Making the Press

Before you begin, examine the bag press assembly diagram shown in Figure 2-5. To assemble the press, follow these steps:

1. Locate and mark the holes in the uprights according the diagram. Drill a 1.5-inch-diameter hole in each 2″×6″ end plate.
2. Secure each 8-inch-long 2″×6″ piece with three long deck screws through the 12-inch 2″×6″ base piece.
3. Drive home the deck screws into the wood.
4. Attach the bracing triangles to the frame using the shorter deck screws (see Figure 2-6). Test the frame for rigidity.

   

5. Center the pipe flanges over the holes in the upright and attach, using the short #12 wood screws (see Figure 2-7).

   

You’ve now built a sturdy bag-holding frame that is capable of withstanding the great stresses juice extraction creates. Next, you’ll put the frame to the test by twisting the bag to squeeze out the precious liquid from your fruit.

To operate the bag press, follow these steps:

1. Place the loaf pan on the frame.
2. Insert a small quantity of soft, juicy fruit, such as grapes or peeled orange sections, into the bag.
3. Insert the ends of the bag through the holes in the uprights.
4. Insert one of the dowels through the pocket, centering the dowel on the flange hole.
5. Tie the open end of the bag around the middle of the remaining dowel, and your bag is finished (see Figure 2-8).

   

6. Now it’s time to squeeze your fruit. As you rotate the dowels in opposite directions, the bag will tighten, squeezing juice into the loaf pan, and leaving the pulp in the bag.

Pressing On

Why does twisting the ends of a cloth tube strung inside a rigid frame put a squeeze on the contents inside it? Well, that’s a more complicated question to answer than you might think at first glance. Take a look at Figure 2-9.

Imagine that the cloth consists only of a great number of horizontal, nonstretchable threads in the shape of a hollow tube of length x (of course you probably realize that there are vertical threads as well, but we’ll ignore these for now). When you twist those threads, the shape changes from a single hollow tube to two hollow cones that are touching, point to point. And since the horizontal threads don’t stretch, and since the rigid frame maintains the distance from the ends as x, the diameter of the cones’ bases shrinks. In other words, the volume of those two cones is much less than the volume of the original hollow tube. The squeeze is on!

If you add another twist, then the two hollow cones become four hollow cones, while the diameter of each cone continues to shrink, putting even more pressure on the contents inside the cloth (see Figure 2-10). This continues until either you stop twisting the ends or the threads rupture.