I tried to send this comment once already but it didn't get posted - my inexperience I assume. Anyway here goes again.
There has been a lot of discussion in the European parliament over the past 18 months about the use of Isinglass as finings in beer and the desirability or otherwise of labelling bottles and pumps to inform anyone drinking the products that they contain a material derived from fish. After much effort by the British MEPs the conclusion was reached that it was not necessary to inform the public that British beers usually contain fish residues and the brewing industry was spared the prospect of having to write "Contains Fish" on the beer pumps. I am interested to hear that Sainsbury's have taken a different approach.
The almost universal use of Isinglass in the British brewing industry is curious - many people ask how on earth was such a process ever invented. I am sure the real origins are lost in antiquity but one thing is certain - it is not necessary. It's use has no effect on flavour (either good or bad). The sole function is to speed up the settling of the yeast after fermentation (a financial consideration). If this clearing has to happen directly in the barrels (real ales) then this is very useful and quick. Leaving the yeast suspended too long is bad since the bursting of the cells can produce an undesirable flavour.
However the statement in Don's contribution:- "2/ It (Isinglass) has never caused a reaction to anyone who is fish allergen sensitive because of its highly refined state" is far from true. Fish allergy (like many other allergies) is highly species specific. One cannot predict whether a person who is allergic to cod, for example, will react to sardines or shark and vice versa. It is certainly well known that many people, who have serious allergies to shell fish, have no reaction at all to "real" fish.
One could argue that pure Isinglass is a collagen with a molecular weight greatly in excess of that of typical fish allergens and as such would not be expected to cause problems. However, an allergic response could be caused by the trace quantities of smaller fish proteins remaining in the product from the manufacturing process. Such materials would be expected to be soluble and remain in the beer even if the all the Isinglass had been removed (unlikely - it would probably take too long). The reaction it produces is, however, quite different to the immediate response caused by the smaller proteins.
It is difficult enough for vegetarians and vegans to avoid foodstuffs "contaminated" by animal products and the unwitting consumption of such materials would no doubt cause them much mental anguish. However, it would not constitute a danger to health. The same is not true for persons with serious allergy. (This is no different from the peanut problem - many manufacturers of chocolate declare that their products "cannot be guaranteed to be free from peanuts" because of chance contamination from manufacturing equipment). Of course, most people who have such extreme allergies are already well aware of their problems and would not be seen dead drinking British beer (sorry!). Unfortunately, this might not be the same for a visitor who could not know that draught beers probably contain fish.
The fact that Isinglass is not necesary for the production of high quality beers is well illustrated by the German market. It is simply not allowed to use materials which remain in the beer (the famous Reinheitsgebot). I think one cannot accuse the Germans of making bad beer - they certainly drink an awful lot of it - much more than in the UK. Even the biggest brand in the world (don't tell me what you think of it) - Budweiser ex USA - uses no Isinglass. Budweiser and Pilsner Urquell from Check Replublic don't either.
After all that, you might find the following very strange. In Germany, Isinglass and gelatin are used in wine production - gelatin got a bad name with the BSE scandal so up went the Isinglass usage. In France, Isinglass is used in the preparation of sugar confectionery (the icing on the cake so to speak). Fish gelatin is used in many countries as a normal component of sweets. One does not find the declaration of any of these materials on the packaging.
Fortunately, there aren't many of us (i.e. people with extreme fish allergy) left!
Happy drinking! Ellerman12