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SAFPP recently had a look at the potential of canning and in particular autoclaving.We believe there is an opportunity to use the home processing equipment used in the USA, but still need to determine the cost of such an approach.

NOTES: CANNING OF LOW ACID FOODS AS A USABLE PROCESS IN SMALL FOOD PROCESSING INDUSTRIES

SAFPP have been grappling with the difficulty of introducing canning of low acid foods into small business, based on cost and process factors. This note collects some information and makes a proposal on an approach that will remove the uncertainty that currently exists and constrains progress.

This document is prepared not as a final statement but to focus the discussion of what is possible. We should see this not only as a solution to the needs of MSEs in South Africa, but more widely to MSEs in Africa. It is also worth looking more generally at pressure processing in small processing enterprises with limited access to electricity.

To avoid the possibility of getting botulism (a very serious and potentially fatal food poisoning) from canned foods, you must process low-acid foods, such as fish, meats and vegetables, at 116ºC. This temperature can only be reached safely only in a retort or pressure canner.

The basic operation (see annexure 1 for a more detailed description) of a retort is:

The time at the temperature must be controlled absolutely correctly and will be different for each tin and product.

A book in publication by CTA[ii] focuses on the fact that the small-scale operation of an retort is expensive and results in the product being unable to compete with cheaper products resulting from the economy of scale of large factories.

On the other hand community food processing centers in the USA provide households with the equipment, training and support to can the meat and vegetables they have produced in their hose gardens. In this environment the complexity of using a canner is recognised but not seen as constraining – rather [iii] good information and support are provided.

The constraints on the application of pressure canning by small food processing enterprises identified above are real but can be addressed as follows, based on my understanding of the SMME environment, in South Africa

This tends to imply that this is not required for other food processing but is in reality needed everywhere and can be put in place in South Africa with appropriate management, training and support. What needs to be addressed here is the type and level of training, control mechanisms and management control required to produce a safe operation.

The availability of appropriate cans is a major issue in many ACP (African Caribbean and Pacific) where they are not locally produced and need to be imported. In South Africa, with our industrial support, availability will not be a problem and the use of pouches ensures that the appropriate contact material is used.

South Africa surely has the necessary infrastructure in place, in particular the SABS’s SMME support section should be approached to understand what is available to the small food processing business.

While capital costs of stand alone retorts and their supporting services (steam, compressed air) are high, there is also the potential of using small (100can) pressure canners as used in the USA home processing centers. An example is the Wells Can Company pressure canner (http://www.wellscan.ca/canners.htm)

The cost of US$ 370 indicates that they could be supplied to a processing center for around R 5 000. These units would then be used on any heat source, even those used to produce the product to be canned or could maybe be fitted with built in heating elements to simplify operation.

If pressure canners are used the operating costs will be strongly dependent on the labour required to operate the plant. The previously proposed retort would have resulted in a capital cost of around 50c a can. A pressure canner producing 100 cans a day (ie one batch) would have a capital cost of only 5 c/can allowing the extra labour costs to be absorbed (assuming 3h labour – ie constant supervision for each batch – this would be 36c/can). This labour cost can be reduced by installing multiple pressure canners and using one operator in a well-scheduled production line.

It seems to be possible to introduce small scale canning so long as the product being canned is for a niche market that is able to carry the higher cost resulting from a small scale operation – note that this is even the case with normally packaged products because of the large cost of buying “small quantities” of packaging materials.

I therefore propose we take a decision to install canned/pouched products at the Richards Bay Food Processing Center using pressure canners.

ü contact SABS SMME section to get their support for a canning operation – note they are generous in their SMME support so they should be pushed hard

ü carry out improved costing on the production and canning processes to confirm the potential selling price. This would start with a clear definition of the operations, focused on producing all the products and using a days operation rather that sales. This will then give a potential production, a cost and even a breakeven production

ü develop a definition of the type and level of training, control mechanisms and management control required to produce a safe operation.

ü once these are established consult with ITDG and CTA to get there response to the system proposed

A pressure canner is used in preserving foods to raise the temperature of the food above 212 degrees F. This temperature is necessary to destroy micro-organisms that cause spoilage.

A pressure canner is safe to use, if handled correctly. Principles for use of a pressure canner include:

Heat is applied to the canner. Water boils at 212 degrees F, forming steam. Steam drives out air through the open vent. Heat begins to penetrate the jar.

As heating continues, air is finally exhausted. Air must be excluded because it interferes with passage of heat. Heat passes through steam more readily than through air. Heat continues to penetrate the jar.

The vent is closed after steam has escaped for 10 minutes. Steam now cannot escape, so pressure rises. Water under pressure boils at temperatures above 212 degrees F. At 5 pounds gauge pressure, water boils at 288 degrees F. At 10 pounds pressure, water boils at 240 degrees F.

Conduction is the means by which heat penetrates the jar. That is, heat passes from one molecule to another. In thick mixtures, heat movement is largely by conduction.

Convection. Heat is also distributed by convection. Heated fluids expand, rise and are replaced by cooler fluids. Convection currents are slow in thick mixtures. They are retarded by fat, tightly-packed food and solid materials. Heat penetrates by both convection and conduction at the same time.

Food, steam and air expand as heat enters, thus, increasing the pressure in the jar. The 1/2-inch "headspace" in the jar acts as a cushion. Since this increasing pressure is still below canner pressure, jar contents cannot boil out against the higher canner pressure when it is held steady. Pressure and temperature in the jar are finally equal to the pressure and temperature in the canner.

At the end of the processing time, the source of heat is removed and active boiling stops. Temperature and pressure in the canner start to fall as the cooling off period begins. Temperature and pressure in the jar slowly follow that of the canner.

If the vent is opened before the pressure reaches zero or too soon after the pressure falls to zero, there is danger of jars exploding. This sudden release of outside pressure permits steam to form explosively in the jar and the liquid boils out.

When the canner is removed from heat and the petcock is left closed, cooling continues slowly. The gauge needle returns to zero. The vent is opened slowly. Air enters from the outside. Too long a delay in opening the vent causes increasing vacuum. This makes the canner lid difficult to remove; jars may spurt liquid; and the gauge may be damaged.

After jars are removed from the canner, the contents may continue to boil as the jar pressure is reduced by condensation of steam. Continued boiling is a good indication that jars are tightly sealed.

The same principles apply to canners with weighted selective pressure controls and vent tube. However, the control which is made for 5, 10 and 15 pounds pressure is set on the tube that also serves as the vent. The periodic jiggle of the control indicates that the air is exhausted from the canner and that it has reached the desired pressure.

Frances L. Reasonover, former Extension foods and nutrition specialist, The Texas A&M University System, prepared the original manuscript for this publication.

ANNEXURE 2

For those new to home canning, using the pressure canner for the first time can be an intimidating experience. Experienced home canners know a pressure canner is a necessity in preserving vegetables safely, as well as for preserving meat, poultry and fish - what we call low-acid foods. It is important to understand why the pressure canner is necessary for these foods, how to select a canner, and how to operate it safely.

A pressure canner can be a lifetime investment. If well cared for, it can outlast several generations! Because older canners may be handed down from grandmothers, or found at garage sales or thrift stores, user manuals may be lost along the way. The rubber gasket may need to be replaced and the dial gauge tested.

The pressure itself does not destroy harmful microorganisms, but the higher temperatures attained by steam under pressure for an adequate period of time do kill harmful bacteria capable of growing in canned food.

Models made before 1970 were heavy-walled (cast aluminum) kettles with a clamp-on or turn-on lid. At least one company still makes the cast aluminum, clamp-on lid type, which requires no gasket. Canners will have a dial or weighted gauge, a vent with a petcock or counterweight, and a safety valve or fuse. Most modern pressure canners are lightweight (pressed aluminum or stainless steel), thin-walled kettles. Most have a turn-on lid with a rubber gasket. The clamp-on type requires no gasket. All canners should have a jar rack so jars do not touch the bottom of the kettle or each other. The vent may be an automatic vent/cover lock, or a steam vent to be closed with a counterweight or petcock. The safety fuse may be a rubber cap that will blow off if pressure becomes excessive, or a one-piece counterweight.

The weighted gauge exhausts tiny amounts of air and steam each time the gauge rocks or jiggles during processing so it is self-regulating. It controls pressure precisely but requires attention by listening so the rocking or jiggling is maintained but not excessive. It does not need periodic testing for accuracy. Some weight gauges indicate only 15-pounds pressure. Others may have options for 5, 10 or 15-pounds pressure. One disadvantage is that it cannot correct precisely for high altitude adjustment (such as 13 pounds for 6,000ft.).

Dial gauges should be checked for accuracy each season before using and should be replaced if the accuracy is off by more than a pound. Low readings may indicate accuracy is unpredictable. (Some Cooperative Extension offices provide this service.) It is sometimes more difficult to regulate the heat under the canner to hold a constant pressure, especially on electric ranges.

Because a pressure canner is a rather expensive piece of equipment, finding a good used canner can be a real bargain. They may be found at garage sales, thrift stores and even grandma's attic. Many early-dated canners are useable, but may need replacement parts and a good cleaning. Replacement parts are sometimes available at variety or hardware stores, as well as from appliance repair shops and manufacturers of today's canners. Generally, old handles and knobs that have cracked and come off can be replaced. Check for any dents that might prevent a good seal when closed. A warped bottom will not make good contact with an electric unit and may never attain proper pressure.

If you have never operated a pressure canner, it's best to do a "trial run" without jars of food inside. This provides an opportunity to watch for steam leaks, check the gasket fit and determine what heat setting on the range seems to hold proper pressure. To do a "trial run":

ü Turn heat to high and leave the vent (petcock) open. When steam appears, allow the steam to vent 10 minutes so that steam, not air, fills the entire canner. This ensures that you will attain the right pressure.

ü Close the petcock (on the dial gauge canner) or put the weight gauge on the vent. If you have a weight gauge canner, be attentive to when the rocking begins and start timing. Adjust heat to maintain a slight jiggling. With a dial gauge canner, when the needle reaches the desired pressure, adjust heat to maintain the pressure. (The required pressure is 13 pounds at 6,000 feet altitude.) DO NOT LOWER PRESSURE by opening the petcock or lifting the weight.

ü Do not leave the kitchen area during the processing time. Keep a close watch on the dial gauge or listen to the rocking of the weight gauge.

ü When processing time is complete, remove the canner from the heating unit. Do not place it in a draft. Let the canner cool, but do not hurry the cooling by using cold water. Too rapid cooling can cause loss of liquid in the jars.

ü When the pressure is at zero, open the petcock. Or, when the weight gauge does not hiss when touched, remove the gauge and open the lid carefully, lifting it away from the body to protect your face from steam.

ü When ready to process jars of food, place jars on the rack so steam can flow around the jars without the jars touching. After opening the canner, remove jars immediately with a jar "lifter" and place on a dry towel or rack with ample space for air circulation. Avoid a drafty area. Fast cooling as well as fluctuating pressure may cause loss of liquid in the canned product. Do not touch the jar lids until completely cool. During the cool-down the jar lid is sucked down and seals. You will hear a ping as each jar seals.

For more detailed information about selection, care and operation of pressure canners, contact your local Colorado State University Cooperative Extension office. Fact Sheets with directions and processing times for vegetables, meats and fish are also available at Cooperative Extension offices.

[i] Intermediate Technology Development Group, Canning of Food, http://www.itdg.org/html

[ii] Barrie Axtell and Peter Fellows (editors), Opportunities in Meat and Fish Processing, Technical Center for Agricultural and Rural Co-operation, in press

[iii] Colorado State University Cooperative Extension. 1995-2001, www.ext.colostate.edu