CD's Keg Fermenting
Chamber
C.D. Pritchard - New,
10/9/99 Updated 11/00
Background
This page details the latest in a series
of fermenter chambers I've made. There were two previous attempts - one
for a carboy that was similiar to Ken Schwartz's Fermenter
Chamber, and the other a water bath for a cornie keg fermenter. Here's
are rough drawings of 'em:
My version of the former eats alot of
ice, has a large footprint, takes alot of storage space and conversion
to cooling via a fan circulating cold air from the fridge would require
2 large holes in the fridge. The water bath chamber was made from the top
portion of a plastic trash can telescoped/siliconed/taped inside the top
of a 6 gal. plastic pail, covered with fiberglass insultation and contained
in a big plastic trash can. It was cooled via pumping the water around
the keg through a heat exchanger made from 3/8" copper tubing in the brew
fridge. It worked OK until the insulation eventually got wet through condensation
and, later, a leak. The lastest one is better that the previous two. The
design criteria was for it was:
-
Control within + - 1 degF.
-
Cooled by either ice or by a heat exchanger
in the brew fridge
-
Small foot print when in use and easily stored
when not.
-
Doesn't eat alot of ice.
First, a conceptual drawing of the gizmo;
more drawings showing the details are further down...
HACKING THE KEG
The Heat Exchanger
The guts of the gizmo is the heat exchanger
inside the keg. It's made from a 3' corrugated stainless steel connector
that's intended for connecting gas to gas appliances. I got it at Home
Depot. Hack the fittings off of the ends leaving as much of the uncorrugted
tubing as possible. Assemble as shown in the detail above and solder with
Stay-Brite silver-like solder (available at hobby shops). The fit between
the connector and the coupling is a bit looser than what I like, so I enlarged
the ends of the SS connector with a swaging tool. The compression fittings
in the keg disconnect posts allow the heat exchanger to be fitted inside
the keg and allows for removal for cleaning. Drill out the compression
fitting so tthe 1/4" copper tube will pass through. Turn down the MPT end
of the fitting so that it's a friction/interference fit inside the keg
disconnect post. I used a "vertical lathe" for this (a.k.a. a drill press
and a file). For one keg, I heated the post to enlarge it then pounded
in the fitting. For another keg I used LockTite. Both have held up well.
Use delrin rather than brass inserts in the compression fitting and don't
torque down the compression nut too tight or the heat exchanger won't be
easily removable! (I'm now using 1/4" SS tubing since it isn't dented by
the compression fitting.)
Hacking the Keg Lid
The fittings indicated in the above drawing
are all mounted via tapped holes in the lid. Allow for enough space between
them for a wrench on the 1/4 fittings and a socket on the larger fitting
and use telfon tape on each fitting. Don't over-torque the fittings or
they will strip- particiliarly the larger one since there's not a lot of
thread engagement. I did a mostly-hydro pressure test to 20 psig after
assembly by filling the keg almost completely full of water, pressurizing
slowly with CO2 and then soap testing the joints. I've not shown it, but
I also modified another keg lid as above but used a 1/2" hard tubing fitting
to allow a bigger cross-sectional area for blow-off. Rather than
tapping the lid, I soldered the fitting to the lid with Stay-Brite solder
after peening over the end of the fitting on the inside surface of the
lid. The temperature probe is a thermistor at the end of a 6" length of
1/4" copper tubing (it's now stainless tubing). The business end
of the thermistor is exposed and the gap between it and the tubing is sealed
with silicone sealant. The racking/sampling port has a length of 1/4" tubing
installed during fermentation. It's used for taking samples for s.g. testing
and evaluation. Like the compression fittings on the keg, both of the above
ports use delrin compression inserts and the compression nut isn't torqued
too tight. It can be replaced with a longer piece of tubing
for racking, but, unless you pressurize the keg with CO2, it makes for
slow racking due to the small ID of the tubing. I usually remove the elbow
attached to the blowoff port and drop in a racking cane. The blowoff port
is fitted with an elbow with a short lenght of vinyl tubing overlapping
the joint. A longer length of vinyl tubing is fitted to the end of the
elbow. If I was doing the lids again. I'd go with the 1/2" hard pipe fitting
soldered in the lid for the primary fermenter and maybe a 1/4" elbow for
the secondary fermenter. Eventually, I'll replace all of the copper and
brass fittings and tubing on the lid and the two fittings on the keg disconnect
posts with stainless steel to avoid any dielectric corrosion. So far (6
batches), this hasn't been a problem. The hassle with the lid is that you
have to sung it place on the keg and then attach the temp. probe, sampling
and racking tubes and blowoff. When filling from the boiler, I rack in
via the blowoff opening and have foam stoppers on the other openings for
air venting.
Keg Insulation
The keg has an insulative jacket made
of 3.5 layers of ordinary sleeping pads (about 5/8" thick from WalMart).
Foam carpet padding can also be used and it's a lot cheaper than sleeping
pads. Can't remember how many pads were used but they were taped
together at the ends and wrapped around the keg with a some paper temporarily
plcaced between the keg and jacket so that the jacket is a bit larger than
the keg OD- that way, the jacket can be easily slipped on and off.. The
jacket is covered with aluminiized bubble wrap. The later cuts down on
radiant heat transfer (and it gives a NASA like look that's cool). The
jacket is sealed tight against the top of the keg with a hose clamp (actually
it's 2 long hose clamps jointed end-to-end). The two "ears" at the top
of the jacket are made from regular duct tape secured to the projecting
layer of sleeping pad for easy removal of jacket. All raw edges are covered
with aluminum (not fabric) duct tape. Here's a drawing with the details:
THE ICE COOLING ASSEMBLY
Here's drawings of the ice container/pump
assembly and how the ice container is made:
I wanted something with low thermal "mass"
so 3 liter PET pop bottles were used for the housing. They're cheap too.
The thing is designed so that there's a dead air space around the 2L ice
bottle. This retards ice melting when the pump isn't on; i.e.- less heat
transfer than if the bottle was submerged in water. For a similiar reason,
the pipe between the ice container and the pump is long so that there's
no water in the ice container yet it's long enough to provide enough NPSH
for the pump. Since the flow is only about 1 qt/min, not alot of NPSH is
required- about 6". The manifold at the top is made from 2 pieces of 1/4"
copper tubing soldered togeter. The lower piece has a ring with 13, 3/32"
discharge holes. soldered to it is a riser. The manifold discharges water
so that it flows down the sides of the ice bottle in a laminar manner.
A hacked top of a 3L bottle was is attached to the manifold and serves
toalign the manifold over the 2-L bottle with ice and hold the manifold
level. The pump used when cooling with ice is a Proven Pump model 3BPLA
pump. Shutoff head is 11' and it's rated 4.3 GPM at 3' of head. It's available
for $29 from Johnstone Supply (a nation-wide Granger-like clone). The thermistor
is monitored by the controller during pumping and sounds an alarm if the
cooling water temp. is too high indicating the need to change the ice bottle.
USE WITH A FRIDGE
The concept drawing above shows the basic
arrrangement when the brew fridge is used for a cooling source. The pump
is a cheap 12 VDC bilge pump from WalMart which I've had for years. It's
inside a 3# coffee can filled about 3/4 full with water (for NPSH for the
pump). The heat exchanger is made from 1/2" type L (thin wall) hard copper
tubing and street and regular elbows and is mounted horziontally below
one of the fridge shelves. Here's a drawing of it:
My brew fridge is an old upright freezer
and has a fan that circulates air over the evaporator and within the fridge
and has a port that blows cold air across the heat exchanger. A fan is
needed for effective heat transfer. The first heat exchanger was made from
3/8" but the friction loss thru it was too much for the cheap bilge pump.
An automotive transmission oil cooler might work well if the friction loss
isn't too much or a better pump is used.
THE CONTROLLER
The controller is based on the Stamp II
programmable microcontroller I also use in the RIMS, HLT and boiler controller.
I've not incorporated the heater and brew fridge control yet, so I'm not
posting the design yet. Currently, it has a LCD and key pad that allows
setting of the desired fermentation temp., the dT for turning the pump
on and off and for setting the alarm temps. It monitors both the
fermenter temp. and the cooling water temp. If any of the temps. get too
high, an alarm is sounded. It has a serial port for dumping data to a PC,
but, I've not strung the wire yet.
USING THE THING
I've done 6 batches I've done so far.
It maintians a fermenter temp. of 55 degF with one ice change per day when
it's located inside the house @ 72 degF. Powered by the fridge @ 45 degF,
it'll do the same with an ambient temp of 90 degF. For dropping to lagering
temp. (which I've not tried yet), the ice gizmo is need. Rather than do
this, I might try putting the keg (with jacket installed to reduce the
dT/dt) in the beer fridge- will probably kill the yeast...
GOING FURTHER
As with most of my gadgets, I expect to
be hacking on this thing. Here are the things I'd like to do:
-
Wire the controller to my PC for data logging
-
A heater for fermenting in the garage in winter.
-
Hack the controller so it controls the brew
fridge also.
-
Add a gizmo to measure the rate of evolution
of CO2 during the ferment. Best brain-fart so far is:
When the fluid in the smaller diameter
tube overflows via bubbles from the overflow, the probes on the fluid sensor
detect the brief rise in the level of fluid. If this doesn't work, maybe
a microphone connected to a filter and flip-flop circuit to detect the
"glugging" sound. The spikes from either device can be counted and the
off-gas rate calculated by the Stamp.
-
If there's enough program memory left in the
Stamp after all of the above (doubtful...), add programming for automatically
changing the temp. setpoint so that it can automatically do dicetyl rests
and automatic drops to lagering temps.
The Fine Print: Lots
of stuff could go wrong if you attempt to make this think and I accept
no blame for any of 'em! The info is liable to be worth exactly what it's
cost ya! (grin)
Return to my Main Page
c.d. pritchard,
r1, 11/01