Processing of condiments – Part 17: Sauerkraut

Sauerkraut is made from shredded cabbage leaves preserved through an acidifying fermentation process. Sauerkraut is produced from both hard white or red cabbage varieties.

Process description

Harvesting of cabbage

Cabbage is harvested by cutting the heads from the stems with sharp knives or blades. This is usually done by hand, but mechanical harvesters can also be used.

Cooling of harvested cabbage

Cooling involves extracting heat from the product to decrease its temperature using an appropriate device such as a heat exchanger and medium, for example water, air, or refrigerant. Water losses (wilting) occur as a result of transpiration (moisture evaporates from the surface cells), respiration and surface damage, which exposes the product to air and further losses.

Process description

Cabbages must be cooled as soon as possible after harvesting to ensure that the best quality is maintained. Most harvested products will keep for a few hours at moderate temperatures, but if they are transported over long distances, the products must be kept at low temperatures. Hydro-cooling is used where the product can be sprayed or dunked in refrigerated potable water (16 to 20 °C). Dunking the product in potable water at this stage also gets rid of some of the residual dirt, dry leaves, and other debris.

The product must be transported and handled carefully to ensure minimal damage. Bruises may result in soft spots, off-flavour development and sites for insect infestation or enzymatic reactions. Products can be transported vertically or horizontally through mechanical methods, for example a simple moving conveyor or baskets in which the cabbages can be loaded. Visual inspection can be performed while the product is conveyed. Roller conveyors rotate the product to ensure visibility on all sides and are used especially for the inspection of products.

Some products are transported in potable water, where potable water acts as a cushion against any possible mechanical damage. The water can be recirculated after filtration and treatment. A flume is the simplest, where a trough (V-shaped) is filled with running potable water.

Different styles of sauerkraut. (Image Source: iherb.com)

Pump systems can also be used where products are transported in a closed pipe to where it will be used and the product and potable water is then separated.

Potable water is defined as water free from suspended matter and from substances that could be deleterious to the product or harmful to health. In addition, the water must be treated by flocculation, filtration, chlorination or other acceptable processes, to ensure compliance with the following microbiological requirements:

Total bacterial count shall not exceed 100 per ml,
Coliform organisms shall not exceed five organisms per 100 ml, and
Faecal coliform bacterial shall not be detectable in 100 ml of the water.

Inspection and sorting of cabbage

Inspection is done on arrival of the cabbage at the processing plant to select the best suitable raw materials for manufacturing the value-added end product. The outer leaves are removed manually while all infected, injured and over mature heads are also removed. The product must adhere to the minimum quality requirements to ensure optimum quality and processing efficiency. Sorting and inspection are very labour intensive practices.

Washing of cabbage

The product is washed in water baths (large containers filled with potable water which must be regularly changed to minimise the chance of any contamination spreading). High-pressure water sprays may also be used to ensure that all surfaces are cleaned. Salt may be added to the water to remove insects and their larvae.

Sorting and trimming of cabbage

This is done to select the best suitable raw materials for manufacturing the value-added end product. Trimming is the deliberate removal of unwanted or unfit fractions of a food product. The product is trimmed and the fibrous stalks removed. Any damaged or immature parts must also be removed. The quality of the product and adherence to pre-set quality standard (colour, shape, and size) must be controlled carefully. Only heads with minor defects can be trimmed.

Inspection of cabbage. (Image Source: haith.co.uk)

Shredding cabbage for sauerkraut

The washed cabbage is shredded by chopping it into 3 to 5 mm fine strips after the core has been removed from the head. The surfaces must be cleanly cut across the cells, or else a limp, discoloured product will result with further processing. Only stainless steel knives, hand driven cutting devices or automatic cutters made from stainless steel should be used.

Care must be taken to ensure that these pieces of equipment are regularly cleaned and disinfected to minimise the possible spreading of contamination. The cutting edges must be sharpened at regular intervals. Blunt cutting edges will damage the product, exposing a lot of cells to air and also tearing the product resulting in a poor, unappealing appearance of the final product. Work surfaces must also be cleaned regularly and disinfected to prevent cross contamination and possible build-up of micro-organisms. The cored cabbage is cut into shreds by thin curved knives attached to a revolving metal disk.

Salting of cabbage for sauerkraut

About 1 to 6% (usually 2,5%) salt by weight is added and mixed well with the shredded cabbage. The salt concentration reduces the growth of spoilage organisms and promotes the growth of lactic acid bacteria. The conversion of cabbage to sauerkraut occurs through a lactic acid fermentation process.

Fermentation of cabbage for sauerkraut

The salted cabbage is put into a closed container with a weighted cover.

Sufficient pickle (brine) is formed through the release of water from the cabbage tissues in which the salt is dissolved. This brine completely covers the cabbage. The brine also contains dissolved sugars, nitrogenous substances, minerals, vitamins, and other compounds, which act as growth medium for the bacteria and yeast naturally present on the cabbage. Bacteria and yeast develop rapidly and a lot of gas (carbon dioxide) is produced during the initial stages of fermentation that ensures removal of oxygen present. Yeast may produce a small amount of alcohol during the initial stages of fermentation.

The initial fermentation period of 3 to 6 weeks is lactic acid fermentation until a final pH of 3,5 to 3,7 is obtained. The organisms naturally present on the cabbage are responsible for the fermentation. (Sometimes starter cultures need to be added.) The predominant organisms are the lactic acid producers (Leuconostoc group) which are also responsible for the gas formation, acetic acid, alcohol, and mannitol production during the first 2 to 3 days of fermentation. The acid produced during fermentation (1 to 1,3%) suppresses the growth of putrefactive (spoilage) bacteria. After 2 to 3 days the Leuconostoc group of bacteria is superseded by another type of lactic acid producing bacteria, which produce large quantities of lactic acid. The development of yeast,

Aerobacter and butyric organisms must be kept to a minimum to ensure a good quality product. Optimum processing temperature is between 19 and 21 °C. The acidity rapidly increases during fermentation and is ± 1,8% (lactic acid) at the final pH of 3,5 to 3,7. Fermentation can take place in trays, tanks or other containers that have temperature and humidity control. The material used in the construction of the fermenters should be acid resistant and impermeable to any flavours and odours.

Filling of sauerkraut

The fully fermented sauerkraut may be kept tightly covered under refrigerated conditions for several months, or it may be canned. During the canning process, two alternatives are available, namely the hot fill and cold fill process. If the hot fill is used, the sauerkraut is heated to boiling point, filled into suitable containers and sealed. For the cold fill, the containers are filled, exhausted, and then sealed prior to further processing.

Exhausting and sealing of sauerkraut

Exhausting involves the partial or complete removal of the remaining air or oxygen in the headspace of a can to prevent corrosion of the tinplate and spoilage of the product. Prior to sealing, the cold filled containers are passed through steam before sealing to displace the air in the headspace at the top of the container and thus reduce the oxygen content that may cause undesirable changes in the product such as discolouration. Upon cooling, the steam forms a partial vacuum in the headspace.

Heat processing of sauerkraut (optional)

Sauerkraut may be given a heat treatment in the final retail containers to extend the shelf life and eliminate the need for refrigerated storage. The processor has two options with regard to the type and severity of the heat treatment, namely a pasteurisation or sterilisation (retort) process. Pasteurised products are products that are heat treated in the container to a minimum internal temperature of 66 °C for a specified time. The time of exposure needed to destroy spoilage organisms and pathogens depends on the acidity of the product, container size and type of packaging material. Sauerkraut should have a pH below 3,7.

This necessitates a heat treatment of 30 minutes at 66 °C. As the temperature increases, the required processing time is reduced, within the limits set by the packaging container. Pasteurisation can be performed in open or closed cookers. High-temperature short-time treatment is generally used to sterilise the product and this is usually performed in retorts. Still retorts (batch retorts) may be vertical or horizontal. Horizontal retorts are easier to load and unload. The retort is closed and steam is pumped into the closed vessel. The time/temperature combinations depend on the heat and pressure resistance of the container. A heat treatment of 12 minutes is required at 100 °C while only 3 seconds is necessary at 121 °C for commercial sterility. Inefficient heating results in premature spoilage of the product.

Cooling of heat processed sauerkraut (optional)

After heating, the product requires to be cooled to below 40 °C with cold water. The first stage of cooling takes place in the retort (for sterilised products) and further cooling takes place once the containers have been removed. Cooling prevents over-heating that would result in loss of sensory quality.