Research report

​Scallops Portion Size Study


McLeod, D ;
Loch Fyne Seafarms
Goldsworthy, G

In 2003 the Sea Fish Industry Authority (Seafish) in partnership with the scallop industry commissioned a study to investigate the weight of a scallop portion, in and out of home, in key European markets. The main purpose of the study was to establish some pertinent features of the distribution of the weight of a scallop portion in regions of heavy scallop consumption

The study was prompted following the recommendation by the European Commission for a lower threshold for the presence of domoic acid, a neurotoxin that leads to Amnesic Shellfish Poisoning (ASP). One of the assumptions underlying this decision was an average portion weight of 250g, based on the estimated average portion weight for mussels. This assumed average weight of 250g was believed within the scallops industry to be considerably higher than the true weight of scallop portions routinely eaten by consumers – both at home and in restaurants. Since this assumption was of critical importance, and with far reaching consequences, the study was undertaken to fill this gap in the evidence base, providing accurate and precise details of scallop portion weights through a scientifically robust study, with proper statistical design, rigorous study conduct, and appropriate statistical analysis and reporting.

This report outlines the background and objectives of this study, the project approach and key findings. Sampling occurred both within the capital cities and in provincial regions of five countries of known high scallop consumption (the UK, France, Italy, Spain and Belgium).

The in-home section of the study recruited up to 250 consumers purchasing scallops from retail outlets for home consumption in each country, with up to ten retail outlets targeted in each of the five countries. The out of home section consisted of visits to 100 out-of-home (usually restaurant) settings in each of the five countries.

Almost 1000 individual scallops were also collected across the five countries for accurate laboratory determination of the weight of the scallops (both adductor muscle and gonad/roe separately). These scallops were randomly selected in batches of ten from a mixture of retail outlets, with roughly equal numbers from each of the five countries.

The study was conducted using pre-specified protocols given to trained field workers. Throughout all stages of the study standardisation of measurements and procedures was insisted upon. All statistical analysis was the subject of a pre-specified statistical analysis plan, agreed in advance by the project group.

The following tables summarise average portion weights overall and across countries for in and out of home scallop consumption

Table 1: Average portion weight for scallop consumption in home (grammes)

Retail N Mean SD Median 1st percentile 99th percentile
UK 607 112 59 105 21 287
Spain 990 70 57 56 15 354
Italy 745 83 53 68 19 278
France 720 112 55 103 20 271
Belgium 437 90 50 79 21 273
Overall Retail 3498 93 55 83 19 292

Table 2: Average portion weight for scallop consumption out of home (grammes)

Restaurant N Mean SD Median 1st percentile 99th percentile
UK 5829 147 77 133 26 396
Spain 3868 55 30 49 14 157
Italy 4343 67 40 57 5 201
France 5911 164 59 165 47 301
Belgium 4388 124 57 116 29 280
Overall Restaurant 23340 112 54 104 24 267


In conclusion, combining the two sources (in home and restaurant) the average weight for a notional scallop portion across the EU is approximately 100g, only 40% of the assumed figure of 250g.

Substantial variability was observed across countries, with portion weights in Spain and Italy considerably lower than the UK and France, and Belgium somewhere between these. The heaviest portions on average are served in France, but even at an average of 164g – out of home - this is still only 66% of the assumed 250g average weight.

The 2001 statement on Amnesic Shellfish Poisoning issued by the Committee on Toxicology highlighted the importance of obtaining additional data on the consumption of scallops to the determination of threshold levels. This report represents an important piece of the jigsaw in the discussion of threshold levels in providing intelligence on the purchase and consumption of scallops across five European countries. The findings and statistical approach will also have a valuable contribution to make to the planning and interpretation of future toxicological studies.

Project Code: S02018

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