Shelf-Life and Storage Issues 7.1 What does the term ‘shelf-life of a product’ actually mean? From the retailer and consumer perspective, the term is normally used to refer to the ‘best before’ date that is the latest date on which the product is said by the manufacturer to be in an acceptable condition for consumption. The term ‘best before’ should not be confused with ‘use by’. The latter is normally employed for products which carry a high risk of microbiological deterioration or contamination, particularly by pathogens, if the date is exceeded. It is rarely used for soft drinks or fruit juices except for freshly squeezed juices. Shelf-life should apply to expected typical rather than idealised storage conditions and some possibility of adverse storage conditions should be explored by the manufacturer and built into the period declared. There will always be situations where products are not stored ideally and complaints may arise. However, to provide the consumer with the best possible advice the product label should be used to indicate specific storage needs. For example ‘store in a refrigerator after opening’ or ‘keep away from light’ could be incorporated into a label. There may often be a tension in determining the ‘best before’ date between the sales force who want the longest possible shelf-life and the quality and technical personnel who may wish to take a more cautious approach. In practice the shelf-life is often finally determined by commercial considerations such as the time taken to get the product onto retailers’ shelves and the minimum life acceptable to the retailer.
7.2 Can the shelf-life of a product be accurately predicted? Knowledge of the manufacturer and in particular, the development team, should enable a reasonable estimate of the shelf-life to be made when a new product is formulated. If the development is a new flavour with little other change, the shelf-life estimate is usually taken as being the same as other products in the same ‘family’. The introduction of new ingredients or the requirement to make a vitamin claim does impose a need for shelf-storage testing to be undertaken before the product is released to the market. Soft Drink and Fruit Juice Problems Solved. http://dx.doi.org/10.1016/B978-0-08-100918-5.00007-2 Copyright © 2017 Elsevier Ltd. All rights reserved.
Soft Drink and Fruit Juice Problems Solved
Even where the change is only the introduction of a new flavour some shelflife testing is desirable. Use of accelerated storage at elevated temperature (40°C) will usually give an indication of significant problems. At this temperature, 1 week of storage can be taken to approximate to 1 month at ambient. The outcome of 3 months at elevated temperature can thus be taken to indicate approximately 1 year at ambient although some changes, particularly to colour and sometimes flavour, may be more pronounced under the elevated conditions. It should, however, be emphasised that there is no real substitute for a full required shelf-life storage particularly when a claim such as a vitamin content is being made.
7.3 What are the main factors affecting the shelf-life of a product? 7.3.1 Microbial condition Unless produced in a domestic situation for immediate consumption, soft drinks and fruit juices cannot exist without packaging. So the most important factors that influence the shelf-life of a soft drink or fruit juice are its ingredients, the processing it receives, the packaging into which it is put and the conditions of storage and its microbiological condition. For the majority of products pasteurised by one means or another, there will be no microbiological deterioration during an indefinite shelf-life. However, for fruit juices sold as freshly squeezed and for which no pasteurisation has been used the shelf-life will be limited to a few days dependent upon the temperature of storage. The other vulnerable products are those juices that have been freshly squeezed but have only received a ‘light’ pasteurisation and have not been packaged aseptically. In such cases shelf-life can be up to about 12–15 weeks provided that products are packaged in a clean environment and stored chilled (i.e. 0–5°C). Carbonated soft drinks with simple formulations that exclude fruit will also generally have an unlimited microbial shelf-life. 7.3.2 Oxygen The presence of dissolved oxygen in products is likely to be damaging to both flavour and colour. Products with citrus flavours are especially vulnerable to oxidative changes. Oxygen levels can be minimised at packing by appropriate flushing of containers by inert gas and subsequent oxygen ingress through the packaging is determined by the packaging used. Glass cans and laminated board packs will very effectively prevent oxygen ingress in most cases and plastic containers vary in the amount of oxygen they will admit to the product. When carbonated products are being produced, dissolved oxygen can limit the level of carbonation and can be a particular problem with drinks such as mixers requiring high carbonation levels.
Shelf-Life and Storage Issues Chapter | 7
7.3.3 Light Exposure of products to strong light will often accelerate flavour and particularly colour deterioration. To limit the effect of light, products should be packed in containers such as cartons or cans that either reduce or do not allow light to pass. For clear containers such as glass and PET that have many other benefits, light ingress may be minimised by appropriate use of secondary packaging or wrap-round labels. 7.3.4 Heat Many products are subjected to heating of short duration during the pasteurisation process. Such processing will sometimes make a small but acceptable change to the flavour. Post production, products should be stored as cool as possible. Storage at up to around 20°C (normal UK warehouse conditions) is normally satisfactory and has little or no effect on the products during stated shelf-life. Above this temperature, there are likely to be progressive negative effects on the flavour and appearance of products. For example continuous storage at 35–40°C is likely to speed normal storage at 3–4 times the rate of normal deterioration. Controlled sample storage at these temperatures is widely used as a means of obtaining early predictions of shelf-life effects.
7.4 What other factors affect shelf-life? 7.4.1 Raw material selection The correct selection of raw materials is essential to obtaining final products of good quality and, after appropriate processing, the required shelf-life. The required type and quality of materials will have been selected during the development phase and it is important to adequately specify the details to ensure the required quality is maintained during production. Many raw materials for beverages are sourced from a variety of countries and the supply chain can be much extended. Important factors that will affect end product quality include the age of the ingredient and conditions of storage. Supply chain and supplier audits will greatly assist in ensuring quality and, for ingredients such as fruit juices, authenticity. Examples of problems that can arise from raw materials include the introduction of microorganisms resistant to normal processing and essential oils that are showing oxidation. 7.4.2 Processing issues The quality of a product and hence its shelf-life, may also be affected by processing employed and the choice of packaging. As indicated earlier, the use of pasteurisation will normally provide effective microbiological stability. However, problems may occur during the pasteurisation process which affect the
Soft Drink and Fruit Juice Problems Solved
stability of the product and its shelf-life. Examples of such problems include pinholing of plates in a flash pasteuriser and blockage of water sprays in a tunnel unit. Depending on pressure differentials, pinholed pasteuriser plates can allow contaminated cooling water to enter the product stream. The regular checking of the integrity of flash pasteurisers by the use of various technologies is therefore highly recommended. Where tunnel pasteurisers are employed, it is important to check that all the water jets are free flowing and not blocked by limescale or other debris. Blocked jets can mean that the expected temperatures of some products in the pasteuriser are not reached with corresponding effects on product microbiological stability. The use of excessive time/temperature regimes in the pasteurisation process, whilst producing the required level of microbial stability, can have significant effects on the physico-chemical stability of the product such as damage to flavour and colour. This can often be detected as a ‘cooked flavour’ and darkened colour especially in juices. This excessive processing most frequently occurs when flash pasteurisers run on recirculation as a consequence of a downstream stoppage. 7.4.3 Packaging issues This is dealt in more detail in Section 7.5 on quality but as indicated, packaging plays a major part in the shelf-life and stability of products. Packaging is an integral part of the product offered to consumers and it is essential that it is selected and evaluated to meet the desired market needs and provide the best protection to the contents but also taking account of commercial factors such as weight and cost. Factors to be considered which will often be dictated by the packaging facilities available, should include container type (bottle, can, laminated carton, etc.), selection of material, closure and secondary packaging. Understanding of the packaging likely to be employed is important at the product development stage to ensure ingredient compatibility. This is especially important if products are being designed for use in cans as some ingredients can cause rapid corrosion or promote metal uptake. Exclusion of sulphur dioxide is also essential as if present, there is a risk of its chemical reduction by the can metal to produce hydrogen sulphide. Can manufacturers will normally carry out compatibility testing before supply.
7.5 Should the shelf-life of products be monitored on a regular basis and if so how is this best carried out? It is important to carry out regular monitoring of product shelf-life as a means of ensuring that product reaching the consumer is of the required quality. Even when the product at manufacture is of the required standard, small changes in
Shelf-Life and Storage Issues Chapter | 7
raw material and packaging quality that may not be picked up on QC checks can affect shelf-life. All products should in any event be tasted for acceptability at production. The most satisfactory means of achieving this is to take regular (case) samples from production on, say, a monthly basis and keep them within a typical warehouse environment as being representative of the way in which product reaching the trade will be handled. Such samples should be held at least until the end of their stated shelf-life. Samples may then be withdrawn from each case throughout the stated shelflife and submitted to an experienced taste panel using a relevant test to assess acceptability. The question of what is an appropriate reference standard against which products are to be tasted will be taken locally. It may be considered that the latest fresh acceptable batch should be used or samples from each case could be held refrigerated and used as references. To minimise the risk of flavour drift, many manufacturers check current production against both the previous production and the batch preceding that. Another key reason for maintaining and monitoring batch samples is to be able to respond appropriately in the event of a complaint arising.
7.6 Why do products need a long shelf-life and how can this be maximised? There is invariably a tension between the quality team who want products to be of the best possible quality in all the circumstances and the marketing staff who want the longest possible shelf-life to meet commercial needs. The length of a product shelf-life, particularly in relation to that of relevant competitor products, may affect the decision of a retailer about whether the product should be stocked at all. Most retailers will set a minimum percentage of a product’s shelf-life that must be available when it enters their system. Individual manufacturers will then wish to examine their storage and distribution chain to establish both the minimum and typical time that products take to reach retailers’ shelves. It will then be possible to evaluate the opportunity for supply. Typical shelf-lives for fruit juices will be from a few days in cold chain distribution and sale to around a year for long-life products. Similarly, most soft drinks will be sold with around a 12 month shelf-life. Particular care needs to be taken with products that carry a claim, especially for a specific vitamin as the claim must be sustainable throughout the shelf-life of the product. Such products require careful formulation with sufficient overage of the vitamin to ensure claim compliance at the end of shelf-life. For mineral claims, it will be normal practice to add a slight overage of, say, 5%.
Soft Drink and Fruit Juice Problems Solved
Leaving aside the issue of claim compliance, which usually requires a shelflife to be limited, shelf-life can often be maximised by careful selection of primary and secondary packaging. Recently, food waste aspects also have to be given consideration.