Quantifying postharvest losses is important for -

    • agricultural policy formulation
    • improving food security (e.g. can contribute to cereal supply estimates)
    • better targeting of loss reduction programmes, and
    • monitoring and evaluating loss reduction activities

Quantification can be achieved by actually measuring the weight/quality loss, by estimating these losses or by asking the opinions of well-informed individuals as part of a questionnaire survey. All three approaches have their problems. Direct measurement of losses provides accurate data but the process of collection is time-consuming and expensive. Estimates are quicker and cheaper to obtain but less precise. They are derived by calculation form generalisation, projection or modeling with external factors. Depending on the quality of the assumptions made for this derivation, estimates may or may not be accurate and will never be as precise as direct measurments. For example, as losses can vary greatly from one location to another and between seasons, estimates derived from another locality or a previous season may not be very representative of the whole population of loss values. In contrast, questionnaire survey data can be undertaken relatively quickly and consequently the data is less expensive and may be more comprehensive than direct measurements. However, although questionnaire respondents may be good at expressing their perceptions or their priorities they may have little idea of the actual extent of losses, especially when these occur slowly over an extended period.

The Global Food Loss & Waste Measurement Protocol

The Food Loss & Waste Protocol (FLW Protocol) is a multi-stakeholder effort to develop the global standard for measuring food loss and waste. It will enable countries, companies and other organizations to estimate in a credible, practical and consistent manner how much food is lost and wasted and identify where the loss and waste occur. With this information, users will be better equipped to address food loss and waste.

The vision of the FLW Protocol is that wide use of the measurement standards will empower the world to minimize food loss and waste, thereby enhancing food security, economic growth, and environmental health. Development of the FLW Protocol is being coordinated by the World Resources Institute (WRI) in conjunction with the Consumer Goods Forum (CGF), FAO, FUSIONS, UNEP, World Business Council for Sustainable Development (WBCSD), and WRAP.

Under the coordination of WRI, Bruno Tran, Grain Postharvest Scientist at NRI, is chair of the Upstream Technical Working Group which is tasked with developing the technical content of the FLW Protocol for upstream value chain activities: from harvest to market. Barbara Leach, of WRAP, is chairing the Downstream Technical Working Group.

M6 Tran

Bruno Tran introduces the work undertaken on the FLW Protocol in the following video:

Click here to access the Upstream Technical Working Group page. This page is used as the central poster board and timeline by the U-TWG to coordinate the tasks and update timeline progress.

Measured food losses

The easiest food commodities for the collection of measured loss data are the grains of cereals and legumes (pulses). Unlike other food commodities there are some agreed loss assessment methods for grains. Grain have two features that make loss measurement easier than for other food types. The first is that grain deteriorates quite slowly compared with perishable foods. This gives an opportunity for the postharvest practitioner to determine what quantity of grain is present at the start of the process. Subsequent loss measurement does not have to be very frequent (i.e. not more than once every four to six weeks).  In contrast, the rapid deterioration of other food, such as fruit and vegetables, requires much more active and speedy loss assessment. Second, grains are small and relatively uniform. This is useful because for the purposes of loss calculation it may be assumed that damaged grains differ from undamaged grains only with respect to their damage and that otherwise the two would be more or less identical. It is therefore possible to estimate the weight loss of damaged grain by comparing it with undamaged grain (called gravimetric loss assessment). For other food commodities, each item may be a different size and shape so loss estimation cannot be achieved by comparing damaged and undamaged items.

Avoiding costly routine loss measurement

Obtaining reliable loss data is not an easy process so naturally there will always be a debate about the relative importance of funding the collection of new loss data and funding loss reduction activities. The African Postharvest Losses Information System (APHLIS) addresses cereal loss estimates in a way that helps to reduce the costs of data collection by making use of the data that are already available. It provides estimates of the cumulative % weight losses for cereal grain losses for the provinces of Sub-Saharan Africa based on measured and questionnaire survey data are already available in the scientific literature. The data cover each step in the postharvest chain; the numbers of scientific publications available to APHLIS are show below.

 Weight loss data

 The number of published loss estimates available to APHLIS for each link in the cereals postharvest chain

These data are used to create postharvest loss profiles that are specific to crop types, climate types and scale of farming (small or large). Some examples of profiles are shown below.

Postharvest loss profiles 2

Four examples of postharvest loss profiles used by APHLIS for calculating cereal weight losses

The profiles shown above do not take account of any annual or seasonal variation that may affect loss values. To achieve this, a network of local experts provides information on a range of 'seasonal' factors that affect the variability of losses from season to season and year to year in the provinces of their countires. These seasonal factors influence the rules that govern the way that loss values are calculated so that losses may vary according to season and year. In this way actual losses do not have to be measured everywhere and in every year but instead are estimated based on previous experience (the PHL profile) and observation of seasonally variable factors.

APHLIS displays its weight loss data as a series of tables or as maps that look like this -

Cereal loss maps

By examining APHLIS loss tables in detail it is possible to see the source of the loss data and a quality rating of the data; measured data are rated more highly than questionnaire data. More information on this can be obtained from the APHLIS website and by consulting the section on 'Understanding APHLIS'. Potentially, there are many approaches to loss estimation and when such estimates are quoted it is essential that an explanation is given of how they are derived. In the case of APHLIS, the figures are cumulative % loss in weight from annual cereal production of ready to consume grain incurred during harvesting, drying, handling operations, farm storage, transport and market storage. The loss figures estimated by APHLIS -

1. Reflect losses of quantity (weight loss); quality change is only relevant if food is no longer fit for human consumption (and therefore considered a 100% weight loss).

2. Are from one year's production, i.e. do not include carryover stocks from the previous season.

3. Are reported for national and sub-national units (provinces) which follow political rather than agro-climatic boundaries; loss estimates for any particular area may therefore hide wide internal variations.

4. Do not take into account of any cereal processing losses.