prawn puzzle
THERE are few catering operations which scorn frozen prawns. It is almost impossible to do so, because the prawn cocktail rates as the UK's favourite starter course, and prawns remain a universal and popular sandwich filling.
Yet, as we munch happily through 25,000 tonnes of prawns a year, buying creates problems for the caterer, who has to contend with different species, confusing labelling, disparate pack weights and the scourge of adding water to prawns - glazing - in order to reach a price advantage when frozen.
why are prawns glazed?
Prawns are a delicate product. If they were frozen after shelling, with no further processing, freezer burn with resulting flavour tainting and product damage would occur. To protect the prawn from freezer burn, a glazing level of 8-10% of surface ice is necessary. This is the level of glazing put on the prawn by the primary processors.
Any secondary glazing level beyond this is usually an attempt by the secondary processor or distributor to reach a price point. There is no advantage to the prawn. The adding of further ice to the prawn creates additional weight, so less actual prawn is needed to reach a packing weight, thus allowing a lower price by weight.
In many cases, any price difference on prawns of the same size is merely a reflection of the amount of added ice. Any impression that the cheaper package somehow represents more prawn for less money is just a frosty illusion.
Secondary glazing is done by spraying water over the already frozen prawns as they pass along a conveyor belt. The sprayed water turns instantly to ice because of the coldness of the prawn - the speed of the conveyor belt and the intensity of the spraying determines the glazing level. The prawns are immediately placed in bags and held in cold store, awaiting delivery.
If a glaze level of 8-10% is the amount required to keep the prawn in good condition while in freeze, the level of secondary glazing can be as high as 50% on the cheapest of prawns. Asian warm water prawns usually come with far more glaze than cold water North Atlantic prawns to meet the market expectation of warm water prawns being substantially cheaper than the North Atlantic variety.
As yet, there are no statutory guidelines on how much additional iceglazing a processor canput on prawns, nor isthere any obligation on suppliers to declare the glaze level.
There are some suppliers whose stated pack weight refers to defrosted prawns, some who give both pack weight including glaze and pack weight minus glaze, and some whose printed pack weight states just the glazed product.
IS THE PRICE RIGHT?
The size of the prawn has a great bearing on the price. The market is prepared to pay a far higher price for larger prawns, though there is no significant taste difference. Few of the brands tested on behalf of Caterer & Hotelkeeper by a food scientist at Blackpool and the Fylde College gave a meaningful indication of size in their packaging information.
The size specification is usually indicated as a count of frozen prawns per pound, expressed as two parameters. This would show on a supplier's listing as "North Atlantic frozen prawns, 200-300". The figures means the packer promises a pound of prawns will yield 200 to 300 prawns of roughly the same size.
However, this figure will refer to frozen prawns complete with glaze. High-glazed prawns will appear to be bigger than they truly are once defrosted. They will still fall within their size banding but at the lower end. Beware of prawn counts on high-glaze prawns.
With some of the larger packers, it is possible to specify a grade called ocean-run, which means the prawns are ungraded by size and there will be a wide size variance. A lower price reflects this lack of size consistency.
Quality
Buying prawns of the required quality at the best price requires care. Primary consideration is the net weight content of the pack. The words net weight, or net of glaze, on a pack means the declared weight is the weight of prawns you will have after the glazing has melted - in other words, the real weight of prawns you are buying.
This figure is what is needed to measure against the pack price to determine value for money. Size of prawn and taste are subjective matters, but come into the buying equation.
PACKAGING INFORMATION
The professional caterer needs just basic packaging information. Most important is pack weight excluding glaze, followed by best before date. Prawn count per pound is far more useful than vague descriptions such as "supreme", "large" or "premium quality".
Storage and defrosting information on frozen prawns is useful, particularly on how prawns should be defrosted, stored when defrosted and their shelf life when defrosted.
The widely accepted best practice for defrosting is overnight in a fridge. Prawns should be kept constantly refrigerated in sealed plastic boxes and not allowed to rise to room temperature while being used in food preparation. A defrosted batch should be consumed within 24 hours and freshly defrosted prawns should never be added to existing defrosted prawns.
TASTING METHODOLOGY
The 10 samples of prawn were placed in sterile sealed tubs and defrosted overnight in a fridge. Before the tasting began, each sample was drained in a sieve for one minute to remove excess defrosted glazing.
Prawns were scooped at random from the boxes, using an egg cup to take in a mixture of sizes. Time between removal from the fridge and presentation to the testers was an average of five minutes.
The tasting was done to a matrix so each taster sampled a different product at the same time. This was done to combat bias towards first and last tasting showing up in the results and to avoid conferring over samples. Tasters at no time were told the brand name of the shellfish they were sampling.
There were no additions to the prawns in the way of seasoning or sauces. Some results might have been different had the prawn been presented in vinaigrette or mayonnaise. Tasters were asked to eat only enough prawns to make their judgements and drink water between tastings.
criteria
Judges were asked to pass opinion on colour, size, texture, saltiness and flavour. Each category had five optional answers from which the taster could choose. The choices and how many points they were worth were: poor (1), not very good (2), acceptable (3), good (4), very good (5). With six samplers this gave a maximum score per category of 30. The judges were not tutored on what to look for.
WHAT THEY TASTED
The tasters sampled prawns from 10 leading suppliers of frozen prawns to the catering industry. As some caterers occasionally buy products from supermarkets, products from the Iceland freezer store chain were included alongside those from catering distributors to provide a retail comparison. The samples for tasting were chosen to represent the best-quality prawns in any company's range.
We asked Edward Kramer, a food scientist at Blackpool and the Fylde College, to conduct defrost tests on the 10 brands sampled to reveal glazing levels on prawns. His findings are listed along with the glaze levels the packers gave to Caterer & Hotelkeeper.
Kramer's method was based on the widely-accepted Codex system of measuring ice glazing which uses water immersion to remove the outer glaze but not defrost the prawn itself.
methodology
Weigh 100g of frozen prawns taken randomly from a pack. Place in a colander and immerse in a large vessel of water held at 20º C for 30 seconds, with some gentle agitation.
Remove and allow to drain for two minutes. Reweigh and note the weight loss, converting it to a percentage. Repeat the test and aggregate the two figures.
A count of whole and broken prawn pieces in each of the 100g samples was also done after defrosting and that figure aggregated. The lower the prawn count, the larger the prawn and the higher the price is likely to be.
PRICE COMPARISONS
The chart at the top right of the page gives an approximate guide only, since the price charged by distributors varies according to the quantity a customer buys. Discounts of up to 40% are obtained in some instances. We asked distributors for a typical price, used major wholesale listings or Caterer & Hotelkeeper paid for packs as an anonymous buyer.
It is important to set price per pound against the prawn count. Small prawns which give a high count should always be much cheaper. To make an equitable comparison, the price per pound of defrosted prawns has been calculated using the defrosted information obtained from the packers.
Price information should also be compared against taste findings. Prices quoted do not take account of delivery, which may be free, charged for or collect only.
Since the prawn count has a direct bearing on price, this table can be used in two ways. Decide on the prawn size you require and see what prawns we list around that size. Alternatively, if you have to buy on price alone, see which brands in our list offer the cheapest price per pound of defrosted prawns and refer to the taste panel reports on page 60. There are many more brands available to caterers than those we list here. o
