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A partially-automated medium-throughput homemade cider press with
lasers.

Pressing Cider from 900lbs of Apples

Most people who know me well know I really like apples. I'm a big fan
for a lot of reasons- taste, texture, the fact that they're a symbol
of my favorite season, the sheer quantity of accessible food that can
grow on a single tree, et cetera. Last year, I decided I wanted to
make some homemade apple cider. I bought a small screw press online,
several boxes of apples from a nearby farmstand, and some nylon
strainer bags from a homebrew store.

The process looked something like this:

 1. Wash an apple in some water
 2. Use a knife to cut the apple into quarters or eighths to fit in
    the intake for a kitchen grinder
 3. Push the slices of apple through the grinder, collect the ground
    apple in a nylon bag
 4. Once enough ground apple pulp has been collected, place the bag
    in the press
 5. Turn the press screw by hand until I extract about a quart of
    juice

Some improvements were made such as washing large groups of apples
simultaneously in a bucket of water, but ultimately this was a long
and slow process bottlenecked by both the need to individually cut
apples with a knife before grinding, and the need to physically turn
the screw to press the juice. Enlisting the help of my wife and two
other friends, it took the four of us several full days of work to
produce about 25 gallons of cider. I froze about half to drink over
the next year, and fermented the other half for hard cider.

The new press

As soon as the cider was done, I started planning for the coming
year. A single full basket in the press above produced barely a quart
of juice; we would need something much larger. I found plans online
for a much higher capacity apple press (archive), one which could
both exert more force and hold more apple at the same time. My wife
does woodworking as a hobby and was looking for a project. We sourced
four-quarter red oak and maple boards from a local hardwood seller,
and we (mostly her) got to work. The red oak made the frame and all
other structural pieces, and 1x4 planks were cut and then glued
together to make large 4x4 beams. After fitting the pieces together
into the pre-cut grooves, we drilled through the beams and bolted
them together with half-inch steel threaded rods. Rather than create
a drain from countertop material as in the link above, I reached out
to a metal fabrication shop and had a food-grade stainless steel tray
with a drain made to the exact size we would need. All wooden pieces
that came in contact with the cider- the basket, the press base, and
the press board- were made from maple, and waterproofed with pure
tung oil. With the exception of the threaded rods, all metal used is
food grade stainless steel. In the end, it looked like this.

[press]

The completed press.

[press_in_a]

The press in action, with cider flowing.

The laser ramp

The press is just one piece of the story, though. Other problems
needed to be solved. The plan was to press a full bin of apples,
about 900lbs worth of mostly Red Gravenstein. All of those apples
would need to be washed and ground into pulp, and there were far too
many to easily lift out of the truck in which we would bring them
home.

Between purchasing and pressing, the apples went through a process
called "sweating", which basically means letting them sit in a big
pile for a while to ripen further. They were left in the bed of a
pickup truck in the shade for a week, with a tarp over the whole
thing to keep wildlife from eating them.

To at once tackle the problem of washing 900lbs of apples and moving
them from the truck to the grinder, I built a ramp. One end could be
leaned on the tailgate of the truck to have apples placed on it,
where they would roll down to the other end which delivered apples to
the grinder. I mounted several spray nozzles near the bottom of the
ramp to spray apples with water as they rolled by, effectively
washing them.

It would of course be a waste of water to leave the sprayers running
the entire time we were pressing. Why get everything wet if there
isn't an apple rolling by at that particular moment?

I drilled a hole through both sides of the ramp. On one side, I
inserted a small 5v laser pointer, and on the other side, a
photoresistor. I wired the photoresistor to one of the same moisture
sensors I experimented with in my last project, which is really just
a LM393 op amp wired up as a voltage comparator. Adjusting the
potentiometer, I could calibrate the op amp so that it would output
5V when the laser beam was broken, and nothing otherwise.

The 5V output feeds to the base pin of a transistor, which controls a
12V input to a delay relay. This relay has a circuit attached such
that when activated, it remains open for a period of time determined
by an adjustable on-board potentiometer- for my purposes I set it to
about 8 seconds. When activated this relay allows 120V AC wall power
to flow to a large solenoid, opening a valve allowing water to flow.
Thus, an apple rolling down the ramp would break the laser beam as it
rolled by, triggering this cascade of circuit activations and turning
on the spray nozzles long enough to clean the triggering apple as
well as any apples close behind it.

[laser_elec]

The op amp, relay, and solenoid. The black plastic enclosure keeps
sunlight off of the photoresistor.

The grinder

I had systems to wash the apples, to deliver them from the truck, and
to press the juice from the pulp. The last piece is the system which
created the pulp: the grinder. I wanted something into which the
apples could fall directly from the wash ramp, without needing human
intervention. A large wooden hopper received the apples, and they
fell downwards into a narrowing space to cutting teeth which could
grind the apples to pulp. We cut and glued together a large cylinder
of solid maple into which I embedded cutting teeth, thin stainless
steel strips which I bent at right angles and screwed into the maple.
The cylinder is mounted on an axle and is driven by a 3/4HP AC motor
via a pulley.

[grinder_si]

Side of the grinder, with ramp installed to dump apples directly in.
Normally a plastic cover is over the top, to prevent spray of apple
chunks.

The whole thing is modeled after this grinder design (archive). You
can see a similar grinder in action here. There were a few lessons
learned here. Firstly, the grinder teeth would bend if the screws
were placed too far from the ends. Repeated impacts with the apples
would twist the extremities of the teeth upwards, both ruining their
ability to chop apples and also impacting the teeth against the
grinder housing as it spun. Secondly, the shape of the grinder feed
is very important. A slow and consistent narrowing is crucial for the
grinder to self-feed, otherwise some sort of mechanism is necessary
to push the apples down. I had to add a curved slope into my grinder
housing after it was originally completed for this very reason.
Apples were simply bouncing around on the blades and not being sucked
into the teeth. One final thing I will be changing will be to
decrease the gap between the teeth and the housing at the spot where
apples pass through the tightest space, in order to grind them even
finer. Cider is pressed out of apple cells that have been broken
open, and large chunks of uncut apple in my pulp means the cider will
not be fully extracted.

As apples are ground, they are expelled out the bottom of the grinder
into a waiting bucket which has been lined with a nylon press bag.
The bucket itself is a standard food-safe 5-gallon bucket. One can
purchase these, but it is often easier to go into any supermarket
with a bakery and ask if they have any empties in the recycling.
After any remaining frosting is washed out, they are ready to start
their second life as apple pulp collectors.

Fun fact for the home cider maker- if you only have one variety of
apple but want to take advantage of the different flavor profiles
that blending can yield, there are some tricks you can do during this
process to yield different profiles of cider. One easy one, assuming
you are not allergic to sulfites, is to dissolve a ground-up Campden
tablet in water, in a standard spray bottle. As the pulp comes out
the bottom of the grinder, mist it lightly with the spray bottle. The
spray will prevent oxidation of the pulp, allowing for greater tannin
levels in the cider. Apples contain tannins, as well as an enzyme
called polyphenol oxidase. In an intact apple, these are kept
separate from one another. When the apple tissue is ruptured during
grinding, these molecules are brought together in the presence of
oxygen, and oxidation begins. Preventing this oxidation will yield a
cider that is yellowish-clear, unlike the typical brown, and is more
astringent than cider that has not had this treatment. Note that this
is just one of several different pathways preventing tannin
extraction. For instance, the tannins will also adsorb directly to
the solid material of the pulp. For this reason, the less time
elapses between the grinding and pressing of an apple, the higher
quality cider will be produced.

[grinder_en]

Looking down the ramp to where the apples will fall in, note the
plastic spray shield

The pressing

Once the bucket is filled, the bag of pulp is lifted out of the
bucket and placed in the press basket. Last year, we had to turn a
screw by hand to push down the press board, which had all sorts of
problems. The screw sometimes sheared off small slivers of metal that
had to be picked out. I could only twist the handles so hard, and
keeping the whole press on the ground when twisting hard proved to be
difficult. Additionally, it simply took a long time to screw the
press all the way down and then unscrew it each press. With the new
press, all of these problems went away. The pulp is placed in the
basket, the pressboard is placed on top, and atop that I put a 12-ton
pneumatic hydraulic bottle jack. Those of you that have used bottle
jacks before, especially higher capacity ones, know that they move
very slowly with each pump of the handle. This bottle jack has a
pneumatic hookup for an air compressor, and when connected to one set
to 90PSI, could quickly extend its ram without effort.

Once the ram extended enough to hit the steel pressure plate on the
underside of the top beam, the cider began to flow. With a strong
press frame and a strong jack, I did not hit the limit of either
piece of equipment. Instead, once pressure increased past some
critical point, one of two things would happen. Firstly, the pressbag
would often be pushed upwards through a narrow gap between the
pressboard and basket, at which point pressing would need to cease or
risk an exploding bag. Secondly, if the pressboard successfully
contained all bagged pulp, it could sometimes increase the outwards
pressure at the base of the basket so much that it would lift the
basket upwards off of the drain slats- also risking a bag explosion,
and reducing the applied pressure. Typically, pressing a full bag
with 25-30 pounds of pulp would yield about two gallons of cider
before one of these two things happened.

When pressing was completed, I was left with several hundred pounds
of pressed ground apple, called pomace. Some of this we fed to our
chickens or used as fertilizer, and the rest was given to our
neighbors who keep horses.

Storage

Let's do some quick math on that last sentence really quick. 900lbs
of apples divided by 30lbs per pressing is 30 pressings, which at 2
gallons per pressing yields 60 gallons. A traditional, professional
cidermaker would have some 50 gallon barrels or other large vessels
into which to put large quantities of cider. We're just a single
household, and need to store 60 gallons of perishable liquid.

One of the nice things about cider (in addition to the taste) is that
it freezes extremely well. Frozen cider, when thawed, will taste
almost identical to when it was fresh. We bought about twenty five
food-safe 1-gallon buckets at a local restaurant supply store, and
filled these up to stack in our chest freezer, filling it to the brim
and then some. We will thaw one every other week or so, and have
fresh cider for the entire year until the season comes around again.

[cider_free]

These go down three layers deep.
The differently colored gallon in the bottom row is the result of me
treating the pulp with sulfite water to prevent oxidation, as
described above.

This still left me needing to find a home for another 35 gallons of
cider, weighing nearly 300lbs. One of my hobbies is home-brewing
beer, and I have a number of 5- and 6-gallon fermenting vessels
available. Between the five fermenters I own and the one I borrowed
from a friend, I am able to store nearly all of the cider I needed
to. The quantity remaining after all vessels had been filled, was the
perfect amount to drink and share on the spot.

Fermentation

The cider in the freezer has finished its journey for now. But for
the cider in the fermenters, it is just beginning. I measured the pH
of my juice- it was about 3.4, perhaps a little lower. Accordingly, I
put two Campden tablets per gallon (archive) in each fermenter and
added this to the cider. Note that many recipes only call for one
Campden tablet per gallon- the required number is pH dependent. The
goal is to have about 75ppm of free SO2, and higher pH means a tablet
will yield less SO2. Lesson learned- the first 5-gallon batch I made,
I did not crush the tablets to powder before adding, and the cider
grew mold and required reracking and other rescue methods. All other
batches had their tablets crushed, and none molded.

[cider_clos]

Six large cider containers, full of happy yeasty beasties

I took a hydrometer reading of the cider, and got a specific gravity
reading of 1.040, enough to ferment to about 4.8% alcohol. For those
unfamiliar, specific gravity measures the amount of dissolved solids
in a liquid. Pure water reads 1.000, and dissolved sugars in the
cider increase the density of the liquid, allowing a
partially-submerged calibrated weight to measure the new density.

The potential 4.8% final ABV is too low to safely preserve the juice;
5.7% is really the bare minimum to not have risky keeping qualities,
and for long-term storage it's preferred to be closer to 8-9%. I
added about 7oz of pure glucose per gallon along with some yeast
nutrients, which will bring my alcohol percent up to about 7% once it
is done happily bubbling away. Some of it I plan to increase further
for very long-term storage, the rest will be left at 7% for bottling
and shorter-term consumption.

Next Year

Apparently, subjecting pomace to a high voltage pulsed electrical
field (30kV, 40us and 1kHz duration and frequency) will crack open
intact cell walls and improve yields (archive) for both the tannin
compounds in the juice, and also juice quantity in general. If anyone
has ideas on how to home-build such a system, please reach out.

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