Aseptically cleaner food

This article will focus on processing methods in food manufacture that can be used to manufacture food and drink products suitable for aseptic filling. In-pack processing is considered one of the main competitors to aseptic filling since it is possible to produce almost all aseptically filled products using in-pack technologies. Other competitors with similar claims are hot-filling and clean-filling. Therefore, the article will close by stressing the advantages of aseptic filling that make it an attractive technology and some of the challenges that lie ahead with future markets where aseptic products may find their niche. If aseptic filling is to maintain or grow its market share then its products must feature in the list of product categories considered by the food industry as 'key product trends'. Not all of these key product trends lend themselves to manufacture with aseptic filling, for example snacks and sandwiches. However, aseptically filled products can feature in almost all other categories. Some categories present a challenge to the industry, such as ethnic, traditional and regional, and the future success in terms of growth into new markets depends on how the industry meets this challenge. Any aseptically filled product will have been given a thermal processing step prior to the filling operation in order to ensure a long shelf life. Once the food has been heat treated it is essential that further contamination is eliminated from the holding tube to the filled pack. Preservation and processing methods to preserve foods by heat include traditional technologies such as retorts, heat exchangers, jacketed vessels and ovens, in addition to the newer technologies such as ohmic heating, ultra high pressure and microwave processing. The majority of aseptic systems feature a heat exchanger or direct steam injection into a vessel as the means to thermally process the food. It assumes that the microbiological kill step occurs in a holding tube or vessel, and the high temperatures in the heaters and coolers allow a safety margin that is not taken into account. This can sometimes lead to a degree of excess in the applied heat treatment. Most (if not all) aseptically-filled foods can be manufactured by in-pack processing techniques and so the choice of aseptic filling must allow a clear competitive advantage if it is to be used. Conventional thermal technologies dominate the market (e.g. retorts) for foods other than fruit juices and milk products. This is because in-pack processing has the advantage that both food and package are sterilised or pasteurised together. Sterilisation uses temperatures around 121.1°C (250°F) for a few minutes to achieve an ambient stable food with long shelf life. Pasteurisation is a lower temperature regime, usually between 70 and 95°C, whereby one or more preservation hurdles are present, such as acidity or chilled storage. Retorts come in all shapes and sizes, and can operate with steam, steam/air, raining water, water spray and water immersion as the heating media. They can be static or rotary batch retorts that can be used to process any container type, or can be continuous cooker-coolers suitable mainly for high speed processing of cylindrical cans. Their flexibility makes retorts a strong competitor for aseptic filling. In addition to the strong competition from batch retorts, there is a substantial canned foods sector using continuous retorts to produce foods that could also be manufactured by aseptic technology. Most of these products are in cylindrical metal cans because of their rolling and magnetic properties that are used in the production and transport processes. One of the most efficient types of processing system is a reel and spiral cooker-cooler, in which rapid heating and cooling are achieved as a result of mixing within the can via the headspace and particulates. For example, a steam chamber may be only 11-15 minutes in duration and operate at 125-130 °C. Such effective heat transfer allows high production rates but has the disadvantage of low flexibility with product changeover. Canned soups tend to be manufactured with reel and spiral systems because they are sufficiently 'thin' to allow good mixing by the headspace bubble and any particulates present. However, continuous canning systems are expensive and few are being replaced with like-systems as they wear out. It is the batch retorts with all their flexibility that is a growth area in the food industry, particularly with new markets for heat preserved foods such as cook-chill products with shelf lives in excess of 10 days. Batch retorts are low cost solutions, which include an active market for reconditioned second-hand retorts that offer flexibility in product, process and package changes. Two similar technologies to aseptic filling that offer strong competition are hot filling and clean filling. They both rely on a thermal treatment to control the numbers of microorganisms but differ in the temperature used for the filling operation. Food products are heated using heat exchangers (e.g. plate, tubular, scraped surface, direct steam injection) or in jacketed vessels, but with hot filling there is no cooling step. Hot filling has one clear advantage and one clear disadvantage when compared with clean or aseptic filling. Its advantage is that the high food temperature used in the filling operation (>93-97°C) pasteurises the pack surfaces and so reduces the microbiological loading that is naturally present with most packaging types (reference 'Pasteurisation Heat Treatments', CCFRA Technical Manual No.27). Typically it is the spore-forming micro-organisms such as yeasts and moulds that introduce airborne contamination onto packaging surfaces. Since these are relatively heat sensitive, it is possible to achieve significant log reductions in their numbers through residual heat from the hot fill. This has a major benefit in that it can allow long shelf lives for acidic products and provide extended shelf lives for low acid foods stored under chilled conditions. The disadvantage with hot filling is the thermal and shear damage to food products that can occur while the product is held at high temperature for extended periods of time. This is more pronounced if particulates are present and agitation is required to maintain their distribution within a batch. Delays in filling cause many issues with particulate degradation and product damage such as oil/water separation, and lead to excessive heat treatment. Poor product quality can result from this. Clean filling is an area that has generated considerable interest in the food industry because it can remove the need to hold products at an elevated temperature prior to filling. It also has applications for foods where there is only a minimal thermal treatment (or even none at all) and so higher product quality can be achieved. In principle, a clean fill will follow a heat-hold-cool process in similar ways to that with an aseptic fill. The difference is in the standards that are applied to the equipment cleaning and air hygiene. Benefits of clean filling compared with hot filling are the cold fill where thermal and shear damage are reduced. Good control of filler hygiene may then allow an extended chilled shelf life beyond 10 days for short shelf life foods. This is an area of much interest for products such as soups, sauces and dressings where a mild heat treatment followed by clean filling can be of benefit in raising product quality. The key question that needs to be addressed with clean filling concerns the level of re-contamination within the filling environment because there is only chilled storage that acts as the preservation hurdle once the pack has been filled. Various definitions of clean filling can be found in the literature and from companies associated with the supply of filling equipment. There is also a further category of ultra clean filling in which some differences in the standards of the filler equipment and air hygiene are defined (see Table 3 for some common definitions). For example, an ultra clean filling environment should have laminar air flow compared with turbulent air flow for a clean fill, and there should be a foil heat seal as an additional barrier to prevent recontamination. However, clean filling is a technology that the food industry is investigating for extended shelf life under chilled conditions but it requires considerably more work before it can be adopted for foods that are sensitive to recontamination and microbial growth. In the short term it is likely that clean filling is being, or will be, used for products such as mineral water, carbonised soft drinks, wine and spirits. Aseptic filling represents the ultimate in level of care that must be given to the processing and filling of a food material. It relies on bringing together a sterile food product and a sterile package, all achieved within a sterile environment. Controlling the aseptic condition of each component and that of the transfer between process and filler is critical. Methods to ensure package sterility usually involve a sterilant such as hydrogen peroxide that is evaporated by heat before the food is filled into the package. Immersion or spray allows the sterilant to reach all parts of the pack and lid. There are many types of food product that can be filled aseptically although the most popular are juices and drinks for retail sale, concentrates for food manufacture and non-particulate sauces for food service. Within these sectors, aseptic filling has dominated the market. However, one of the difficult areas for aseptic filling is with particulate foods where there are sealing issues with fibres or particulates bridging the seal area and particulates that settle or rise in a low viscosity carrier liquid . Aseptic filling has yet to make inroads into the markets for these foods. There are four main disadvantages to aseptic filling when compared with the competition from in-pack processing, hot filling or even clean filling: 1. Higher cost of aseptic fillers 2. Low flexibility in pack or product changes 3. Aseptic linkage between process-filler 4. High quoted failure rates, e.g. 1 in 10,000

Failure rates are interesting for aseptic filling. Figures quoted are usually 1 in 10,000 and considered by the industry to be conservative. However, there are no figures available for recent aseptic installations where the knowledge and application of hygienic design has moved forwards from the early days of aseptic technology. Vendors of aseptic filling equipment will indicate that their systems perform to a lower failure rate but have little data to substantiate these claims. No one doubts this but it would be of significant help to the aseptic sector if such data were available. For example, it is difficult to persuade a company involved with in-pack processing to move to aseptic filling with its associated failure rates of 1 in 10,000. Having outlined the perceived disadvantages of aseptic filling we should end on a positive note and stress the advantages, since there are many. Aseptically filled products undergo a heat-hold-cool process, so products are not held for periods at high temperature before filling, as is the case with hot filling. This can provide a quality benefit. One key component of an aseptic filling operation will be the method used to heat and cool the food product in a continuous system. Choice of the processing technology will depend on properties of the food such as its viscosity and particulate loading. Many different processing technologies can be, for example, conventional heat exchangers, more innovative technologies such as ohmic heating, and vessels with steam jackets and/or direct steam injection. The technology should suit the food product and enable a high quality product to be manufactured. The future for aseptic technology is likely to develop in two main areas. There is a huge market that is currently being exploited for low viscosity foods such as drinks where the technology of processing and filling is well advanced and commercialised. Expansion of this market into new product types and packaging formats is taking place at a rapid pace. Opportunities exist for attractive packaging and features such as easy pour nozzles and drinking aids. This addresses the key product trend for convenience and snacking. The other area where aseptic technology can develop is the market for value-added sauces for catering and possibly also the retail sectors. Packing formats in plastic pouches or jars are becoming more popular due to reduced weight and elimination of sharp edges from breakage with glass and metal shards with cans. This may be increasingly important for the catering sector in its drive to control the presence of physical hazards to the consumer. However, sauces are more complex to process and fill than low viscosity liquids and so the technology is likely to be expensive. Profit margins on value-added sauces will dictate how successful aseptic filling is in obtaining market penetration.