Small Scale On-Farm Processing

BEST PRACTICES: Small Scale On-Farm Processing
by Kenneth Sheppard 1/10/05.

The following is my collective wisdom from having processed coffee on this site for about 8 years. Feel free to disagree with or ignore any of it. This workshop is to help facilitate the free exchange of ideas. The Pioneer Farmers got things just about right with very little money and materials. As a modern farmer you have more access to resources that can improve on the systems developed by the early Kona Coffee Farmers.

WHY DO THIS?

1. To become independent
2. To maximize value added and profitability
3. To enable quality control of the entire process
4. Because you want to… usually the prime reason!

RULE 1. ONLY BAD THINGS CAN HAPPEN AFTER THE CHERRY IS PICKED
Your job is to minimize these effects by good processing and storing practices.

RULE 2. See Rule 1.
You have made the coffee as good as it can be at the moment prior to it being picked off the tree by your farming practices. No amount of subsequent processing will counteract any faults created by poor husbandry. But poor processing can and will have a pronounced effect on quality and ultimately your relationship with your customers. THINK QUALITY AT EVERY STEP AND CONSTANTLY IMPROVE YOUR SYSTEM AND METHODS.

HARVESTING & PULPING

• Pick and pulp the same day, or at worst within 24 hours if the beans have been left in the shade. Things go rapidly down hill after that – NEVER leave picked cherry out in the sun.
• Choose a pulper that will process your biggest round in less than two hours. After a days picking, pulping until midnight with a too small pulper ceases to be fun!.
• Throw away floaters. Small farmers do not generate enough to waste the time and energy to process them separately. Most small farms pulp all the cherry then separate the floaters in the fermentation tank. Floating the cherry can be done but it is an extra step and is generally not necessary if you throw away the pulped floaters… It is more suitable for large-scale operations.
• Add a bean separator to your pulper as time/funds allow. This helps sort out the mothers, mis-pulped green beans etc. It generally cleans up the run. The mis-pulps can be re-passed but no more than once – experience/judgment required here on how the pulper is running and the state of the beans.

NOTE: Just a word on mill design, use gravity as much as possible to transfer the coffee thru the process. Pumps are OK but they are expensive, need to be maintained and the pipe system can clog. Keep it as simple as possible.

FERMENTING

The normal tried-and-trusted Kona method is as follows:

• Limit the amount of pulper water and maximize the amount of juice. Clean beans ferment with difficulty – too clean at this point will hamper your fermentation..
• Ferment the beans JUST covered with water/juice.
• You should be able to ferment out within 12 hours (overnight) or a max of 18 hours. Longer than this lays you open to off flavors, see Rule 1.
• At higher elevations where it is cooler, overnight fermenting out can be difficult. To achieve this, insulate the bean tank and/or add warm water or bottles of warm water to get the ferment going. It self-heat generates once it has started. Ideal about 85°F.
• Drain and rinse off the products of fermentation until the beans are not slimy either by multiple washes or by water spray on a screen or shaker, see Rule 1. It is important to get the surface of the beans dry as soon as possible.

However, you might consider “dry fermentation” (data suggest this is the best method) especially at higher elevations. Drain all the water/juice off and ferment the drained beans. The downside is that the residue is sticky and difficult to rinse off; some people pass it thru a sump pump.

DRYING

Most small farms do not have mechanical dryers, although some are appearing now, so will confine comments to sun drying. Most researchers agree that the coffee cup is no different if the drying IS DONE PROPERLY by either method. However, it is easier to screw up with mechanical dryers if the controls go haywire or you are not vigilant. Sun drying is more forgiving; you can over-dry here too but it is harder to do.

• For every 100 lbs of wet beans one has to evaporate about 5 gallons of water, so your sun deck has to do a big job; optimize the design as best you can.
• There are pros and cons on wood versus concrete.
  If you have a flat spot I recommend concrete purely from the maintenance aspect. But it absorbs moisture, takes longer to warm up but then it holds the heat longer at the end of the day. I would avoid screens except for the first day of drying as they do not have thermal mass and expose more of the bean to re-hydration during the night.
• Point the deck into the prevailing breeze not sideways on.
• Try to have the sides open to help remove the blanket of moisture cooked off by the sun’s heat.
• Drying deck capacity: 500 sq ft will comfortably handle a 20 bag round with a nice depth of parchment. It will do 30 bags at a pinch but requires more raking, especially early on.
• Get beans on deck as soon as possible after rinsing and get them surface dry.
• Use a broad tined rake first – the first hour or so is spent DRYING THE DECK so create broad furrows to expose the deck, move the beans into the dry furrows and dry another stripe, repeat until the deck is dry.
• When the deck is dry a smaller tined rake can be used.
• Rake often the first day, then reduce as judgment dictates by conditions.
• Monitor moisture content.
• If by the 6th or 7th day you cannot get the moisture down below 12%, cover the beans at night to stop them reabsorbing moisture. Put beans in a bin or cover a heap with a tarp. Put beans out the next day as soon as the deck gets warm and the overnight humidity has fallen.
• Take beans off the deck when the moisture is about 11 to 11.5%

STORAGE

It is important to note that for every constant ambient humidity coffee beans in storage will reach an equilibrium moisture content. If the humidity does not change then the moisture content will stay the same. At about 60% constant humidity the beans will stabilize out at the required 12%. If the humidity is higher the moisture content will climb, if significantly lower it will drop. A storage atmosphere of 50% and 50°F is often recommended which keeps the beans on the dry side of 12% and reduces the potential for molds forming.

• Conditions for storing coffee on-farm in the tropics is rarely ideal, usually too moist and beans climb up from 11% off the deck to 14% or more prior to new harvest.
• If you are at high elevation you may need to consider renting a storage space further down the mountain, re-drying coffee is not a good idea. It may be less wet down the hill but the temperature goes up, caution required.
• Some people have tried vacuum packing.
• I don’t see a problem with closed containers and silica gel dessicant if the moisture content is monitored, good circulation would be required but I have never tried this.
• Above about 13.5% moisture it becomes virtually impossible to mill the parchment without creating bean paste (yes this is outside the State’s green certification limits but we are dealing with practicalities here). Below 10% beans are prone to cracking during milling.
• I have noticed a vast difference between green bean moisture content vs the parchment, sometimes as high as 5%. I think this results from poor drying and storage, obviously the skin gets re-wetted first so the green bean should be a little drier once the skin is removed; I have seen wetter green than parchment.
• For the above reason NEVER assume a standard difference between parchment and green dryness. ALWAYS calibrate your meter for parchment and green.
• On the same theme NEVER trust your meter without also doing a color and bite test. With experience you can judge moisture within less than 1%. ALWAYS calibrate your meter at least once per year.
• Store parchment coffee for at least two months before milling. YES there is a difference and the flavor is improved as the various sugars etc. do their thing.

MILLING

There are now a few cost effective options for farmers to do their own dry milling with small machines from India, Costa Rica etc. A word of caution, some machines are designated “Hullers” which sometimes but not always means the machine was designed to hull coffee with the cherry skins dried on (Natural Dry). These machines tend to be more aggressive than a true parchment peeler/polisher, and often result in nicked beans which, while it doesn’t effect flavor, don’t look good in the package. However it is fair to say that a huller will peel parchment and a peeler will hull natural dry but not as well as the machine designed for the job.

• Get a machine with a winnowing fan, or make a fan yourself,. With skill and experience this can be adjusted to effectively make a “Catador” or density sorting device. This is the first stage of cleaning up your coffee.
• My own experience is with the McKinnon “Smout” peeler/polisher. I found that one pass was perfect for on-farm roasting but for a bit more glitz if you sell green a second pass gives a lovely sheen to the bean.
• As the beans and parchment skins drop down the chute the updraft of air sucks the skins and light beans away. By adjusting the airflow a lot of the defect beans can be expelled (I usually adjusted the airflow so that I could hear the odd bean rattle down the exhaust pipe).
• Adjustment of the backpressure is critical, throw away the weight and make an arm that can hold washers, with experience you will know how many washers you need for a particular bean moisture but also check the beans coming out to see if you are too heavy or light. Beans at the correct moisture will take a fair weight without damage and will be well milled. Very dry coffee requires less weight or crack damage can occur.  Moist beans need little or no weight or the beans will squish.
• Keep the exhaust clean, as dust builds up and distorts your hard-won setting.
• One of the most difficult things to mill is dieback or unpulped peaberry. The place to address this is at picking and pulping and general good husbandry. If the grading screens do not help remove this then the only option is to hand sort what is left.

NOTE: I have deliberately left out the use of a gravity table as, as far as I know, there is not one available that is small enough or affordable but that may change. There are some small catadors around and this may be a cost effective option for small farms until the magic table arrives.

GRADING

Passing the coffee over exposed screens does a number of things.
Using a first screen sized below the first “official” screen size (16 for Kona No. 1), say 14, allows you to remove a good amount of the brokens and smalls. This alone does a good clean up. The system also allows you to see what is going on, do some hand sort and determine what further steps you may want to take.

• It is currently uneconomical for a small farmer to certify coffee.
• It is unwise to get all your coffee milled all at once to save on certifying costs as coffee stores better as parchment. This assumes that you will be roasting and selling throughout the year.
• There are no grades for roasted coffee! However most small operations roast an “Estate” grade, officially “Select”.

NOTE: A bit of kudos for Estate farmers. I have milled a fair amount of friends’ coffee, when you have a dry mill you acquire lots of friends, and I have found that they easily meet the grade standards required of certification. Maybe it is because your name is made or broken on the quality of your coffee and you take the extra care in husbandry and harvesting. Most estates are passionate about their coffee and want to make it the very best quality they can. The best customers are repeat customers so keep up the good work.

Whether to sell all “Estate” or by grade is up to you, we could discuss the pros and cons about effect on the cup well into the night. Personally I think the Estate grade gives a rounded flavor but some people mix the top two grades and roast the rest separately. There is also some marketing merit in an “all-farm” coffee; purists will disagree. Ultimately it is between you and your customers.

ROASTING

Although roasting services are available, for your coffee to be truly your coffee you need to consider roasting yourself. Service roasting is fine but it costs money, may not be on your schedule but theirs, may not be done to your liking, and in too large a quantity for your sales volume (coffee starts to deteriorates as soon as it is roasted see Rule 1.)

Unfortunately the availability of affordable effective equipment is not that great, even used roasters hold their value.
Can you learn to roast?  Yes you can.
Basically there are two types of roasters that can be used:
the fluid bed or air (popcorn popper) type usually electric fired,
and the drum type which is usually propane fired.
There are pros and cons with each:

• The air type is easier to learn and is generally more forgiving. The chaff is ejected which cleans up the coffee and reduces the cause of some burnt flavors. The bean is roasted mostly by convection which tends to give an even roast.
• The drum type is more difficult to learn because it has more things to fiddle with. The bean is roasted mostly by conduction which can lead to burning. However the drum type is the most “accepted” roaster in the industry.

Learning to roast is a whole subject of its own, and depends on which roaster you buy.