Re: Destemmer design

Thanks for the design, Douglas, but it wasn't really what I was asking for. [Stephen was asking if I was referring to any particular model. I wasn't.]

Like you, I built my own destemmer this year. Mine consists of a

11"x11"x42" bottomless wooden box (with a hinged top and input hopper) in which I mounted a half section of a 10" diameter PVC pipe in which I drilled 1" holes on 1.5" centers. There is a removable paddle assembly, constructed of a 1-5/16" diameter hardwood shaft, and 11 hardwood paddles on 3" centers. The paddles are mounted at a 60º counter-clockwise rotational angle from each other, and a 15º angle from parallel to the shaft. There is 1/8" clearance between the paddles and the "destemmer basket". There is a 28" bicycle wheel for a flywheel/crank. I plan to add a motor at a later stage. The whole assembly is then mounted above my crusher, using its input hopper as a collection chute. The last 6" of the open bottom are outside of the collection chute, so the stems can drop into a waiting bucket.

But I am disappointed with the results. Too many berries remain on the stems, and too many stems get through. I know that the holes are not too large (they are the same size as in the destemmers one purchases, and it doesn't work well with smaller holes (I tried that last year). I know that the basic paddle design works. Most of the berries fall off the stems, and most of the stems are exhausted out the back --- just as they should. So, it must be in the paddle design, or the rotational speed.

The cheaper "commercial" destemmers have fewer and wider paddles, mounted at 90º angles. The more expensive ones have narrower and more paddles, mounted at anywhere from 30-90º angles. The axial angle varies from 0-30º.

Rather than continue to play around, and make design changes by trial and error (especially since there is only one harvest each year), I'm trying to find an engineering discussion of the principles involved. Some of them I know, and some of them I have guessed, but I'd rather benefit from the research and experience of the industry, than try to reinvent the wheel.

I'm impressed by your rather innovative design. I do have some comments and suggestions:

1) An inexpensive way to motorize it would be to obtain the pulleys and motor from an old evaporative (swamp) cooler. People generally replace them when the bottom rusts out and they begin to leak, even if the other parts are intact. If you were to buy the parts new, it would cost about $50 for motor and pulleys and drive belt. EC motors are made to be used in wet environments, so you can hose off your destemmer to clean it without worrying about harming the motor (unplug it first of course).

2) Galvanized wire contains zinc, which is toxic, corrosive, and not the best thing for one's wine. Even though there is limited contact time, and it has been used for this purpose by homebrewers since (at least) prohibition days, I would be wary. That's why I chose to drill pvc pipe. Ideally, one would use stainless steel, but it is quite expensive.

3) I like the idea of using the irrigation hose for paddle/fingers! It is flexible enough to rub against the destemmer basket without fear of jamming, but sturdy enough to dislodge the berries! Have the staples held up, or do you have fingers coming lose and needing replacement or reattachment?

4) The way to get the stems to discharge without having to angle the destemmer toward the rear is quite simple! Archimedes Screw!

If you mount the paddle/fingers such that they form a helix, the stems will be forced to move down the shaft! Assuming you are turning your shaft clockwise, the paddles should be mounted so that each one is counter-clockwise to the previous as you move down the shaft.

In other words, mount them from front to back at 12 o'clock high, 11 o'clock, 10, 9, 8, .... This gives you a 30º rotational angle, which is the most efficient helix.

You could decrease the angle to 60º, as I've done (e.g. 12, 10, 8, 6,

4, 2...), and it would still work. A 90º angle (12, 9, 6, 3, ...) also works, but less efficiently. And you can use a double-helix for even greater efficiency (i.e. speed of movement from front to back).

Angling the paddles 15-30º to the rear enhances the effect of the screw, just as thread (or propellor) pitch does.

Of course, if the helix is too efficient, and the rotational speed is too slow (which I think is my problem) the stems will exhaust before all the berries are removed. It appears (from what I've seen) that the less expensive hand-cranked models have far fewer paddles than the large commercial motor-driven ones. If my theory is correct, the faster the rotational speed of the shaft, the faster the stems can be discharged, and thus the more tons per hour can be processed.

So my problem MIGHT be solved by using a reduction gear to increase the shaft speed with respect to the flywheel, or by motorizing it. But if you destemmed 30 gallons (~150 pounds?) of grapes through in 20 minutes, perhaps I should just copy your paddle design!

I didn't have access to a lathe, so I used a piece of round stock, and drilled one end to insert a piece of threaded rod (for the flywheel).

Now I really feel bad. I was mulling over various designs for 2 years, and when I finally made up my mind, it took me several days to build. And then harvest day, the results were disappointing. I should have posed the question sooner. :(

Thanks for the helpful input. :)

Making a crusher should be simple.

The hopper's not too difficult to construct, if you have a pattern. (Otherwise you need some fairly complicated math to figure out the length of the sides and he angles. I can send you a computer program that will do it for you, if you'd like).

If you make a jig, you can cut the fluting and round a square piece of hardwood at the same time for the two rollers.

Then all you'll need is a couple of gears and something to use as a crank/flywheel.

You can put the crusher rollers in the input chute to your destemmer, and gear it to your existing crank. It would appear that a 6:1 ratio is used in machines that operate this way.

However, it is far better to destem first, and crush afterwards. Otherwise, you crush some of the stems, and end up with some of the bitter flvaours that you are destemming to avoid.

You could also put the crusher rollers in the output chute of the destemmer (which is where they are in the more expensive machines), and still gear them to the destemmer crank!

Anyway, I'm still interested in finding some engineering data discussing the principles of design used in destemmers, if anyone know of any. :)

I would love to see a few pictures. Any chance of you posting some pictures to alt.binaries.pictures.misc or sending by email. A friend and I while doing the milk crate method this weekend (12 cases) discussed the operation and the possibility of building one.

thanks

What is the "milk crate" method?

Kent, You take a milk crate and place it on top of a tub or bucket and scrub the grapes off the stems. Labor intensive but effective.

John,

How is this process more effective/effecient than just stripping the grapes off of the cluster by hand?

Thanx-Mac

Unless you plan on processing several tons per hour, the centrifugal design is way beyond over-kill.

The "cheap" $300-500 models are more than adequate for home use --- except they crush the grapes BEFORE destemming (which releases many of the bitter components we are destemming to avoid) and they are made of painted steel (which eventually chips and flakes and ends up in the must) rather than stainless steel.

By spending $500-1000 (plus $150-200 shipping), you can obtain a stainless steel crusher with a large hopper and auger feed, but you have to spend over $1000 (plus shipping) for a destemmer with the crusher rollers in the destemmer output chute And you have to spend considerably more for a destemmer where you can vary the percentage of the grapes which are destemmed (for those who wish to do partial carbonic macerations), or the percentage of stems which are retained (for those who wish increased tannin levels and "green" flavours).

I'd still be > How is this process more effective/effecient than just stripping the grapes

You obtain more leverage, and are removing more grapes with one motion. Such a "scrubber" will take about 1/4 - 1/3 the time of "just stripping the grapes".