It all started with a Tweet. “Are you watching Only Connect?  There’s a round about lipids” came the missive from an excited lipid-watcher.  To my lasting regret, I was not in front of BBC2 at that moment.  I did however catch it on iPlayer a day or two later.  The round included sunflower oil and suet.  The latter was the one that stood out to me.  Suet is something I had heard of as being in pastry, and definitely in mince pies, so I was sure it did actually exist, but wanted to pin down why it was grouped with things like olive oil and sunflower oil.

My first port of call was the bookshelf.  Michel Roux’s book ‘Pastry Savoury and Sweet’ makes no reference to suet, and perhaps more surprisingly, neither does my concise Larousse Gastronomique.  Delia makes just one reference to it in her Complete Cookery Course, as an ingredient in savoury pastry, but this is not quite a treatise on what suet is.  What she does say, is that it is a heavy fat from beef.  Although this is by no means wrong, lipid chemists would refer to it as a saturated animal fat, mainly composed of stearic acid.  More specifically, the suet sold in supermarekets is actually pebbles of fat that have been caked in wheat flour in order to stop them sticking together.

But where it comes from is a bit more gruesome: it is the fat used by the bodies of cattle, sheep and pigs to cushion abdominal organs such as the kidneys. When it is first removed from a carcass, it is therefore a sort of white lump.  However unpalatable this may seem on the face of it, in order to make our own bodies properly, similar materials are useful to us.

As all ardent bakers will know, is impossible to make pastry without a source of fat. Generally this is butter, and just occasionally it is from another source.  For savoury pastry, such as that in a esteak and kidney pie, it is seen as ideal as it goes well with these flavours.  Beef dripping can also be used, but this is the fat from beef that has been cooked.  However, as this is liquefied, it will have lost some of the constituents that would otherwise be in suet, such as the protein.

So, we have our answer. Suet is indeed not really a lipid, but a fatty isolate from raw animal carcasses.  It is also typically as fatty as olive oil, but, as it is saturated fat, it is a solid at room temperature.  That makes it a bit tougher than oil, and actually tougher than butter too, and, as anyone who has rolled several types of pastry will know, that makes it easier to roll out.  Also, the fact that it is a solid at room temperature means it can give a thicker texture to foods such as mincemeat.  No wonder it has been used for hundreds of years for making the perfect pie.