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from which the cooker is made. There are two choices – aluminium and stainless steel.Aluminium is significantly cheaper and models tend to weigh less than stainless steel versions of the same capacity. There are several grades of aluminium both in terms of thickness and finish. Its main weakness is that lower grades may tend to interact with food, either causing discolouration or leaching into items that will later be ingested. Foods most likely to interact are those that are quite acidic, for example tomato sauce. But even non-acidic food may cause a grey discolouration that is, in fact, oxidization. Higher grades of aluminium are anodized – put through an electrochemical process that hardens the exterior of the metal so that interaction with food is less likely to happen. There are also degrees of quality for anodizing – “hard” anodized is better. Some forms of anodization allow the metal to have a coloured exterior. Thicker grades of aluminium, particularly at the base, will have better and more even heat distribution – this is important, for example, when you sear meat in fat prior to the actual pressure cooking.Stainless steel does not suffer from the discolouration problem. Again, there are several grades and in fact all or nearly all stainless steel pressure cookers have bases that also contain an enclosed layer of some other metal such as aluminium or copper. That’s because stainless steel is a relatively poor conductor of heat, while the aluminium or copper is far better. Stainless steel is itself an alloy of iron and chromium or iron chromium and nickel. Stainless steel 18/10 consists of 18% chromium, 10% nickel and 72% iron.Internal coating A few manufacturers offer models with an internal non-stick protective coating such as Teflon. On the whole, such coatings should be avoided, unless of extremely high quality, and are not really necessary. Non-stick is useful when frying, but most pressure-cooking recipes consist either of steaming, when there is water or other fluid in the base, or simmering, when there is also fluid in the base. In time, all but the very best non-stick surfaces will degrade, the more so if they come into contact with metal tools and the like, which can cause scratches. In pressure cookers, the problems are the trivet and separators.
2 Then we must consider SIZE. A good average “family” size is about 6lt (10½pts or about 6 US quarts). This will cope with most meals. Larger pressure cookers are available, up to 12lt (21pts), but in addition to their increased cost and weight they also take longer to come up to pressure, so that overall cooking times are increased – and along with them associated heating costs. Very large pressure cookers are sometimes referred to as canning cookers, as they can be used to preserve food by canning – this used to be popular in some countries such as the USA, though most people would now go for freezing as an easier and better form of food preservation. A large pressure cooker usually makes sense for a large family or in a catering situation. Smaller pressure cookers are also available, some with capacities as low as 1.5lt (2¾pts). These are mostly aimed at people going camping where the advantages of small size and rapid cooking but with restricted forms of heat make this a good choice. Otherwise, 4-lt (7-pt) capacities can make sense for 1- or 2-person households, but often the smaller-capacity cookers are not significantly lower in cost than the “standard” 6-lt models.
3 What is the PRESSURE at which the cooker operates? Not all pressure cookers operate at the same pressure. Until relatively recently there was a generally agreed standard of 15 psi, which is twice the pressure of the atmosphere. This requires a little explanation: ambient atmospheric pressure at sea level is 15 psi, so that “15 psi” is relative to ambient pressure (that is, normal air pressure). Most of the general recipes you will find in books and on websites assume 15 psi. But many pressure cookers on the market operate at less than this, often 12 psi or as low as 8 psi. The lower psi figure means longer cooking times and hence less benefit from the method. Manufacturers go for these low pressures because they can save money and also lower the weight of the cooker. A pressure cooker needs to be engineered to be able to cope with accidental overpressures of 6 times normal operation; 90 psi for a 15-psi model, and only 72 psi for a 12-psi version. The lower requirement means savings in the fabric and engineering quality of the cooker. Some manufacturers refer to the pressure by other measurement units – 15 psi is 1 atmosphere (again, this is relative to ambient pressure), so that 12 psi is 0.8 atmosphere; 15 psi is also 103 kPA (kilopascal) and approximately 1 bar. The recipes and tables in this book are based on 15 psi, but with reminders about how to extend for 12 psi and below – this usually means having to add 20% to the cooking time.All but the lowest-priced pressure cookers also allow for cooking at lower pressures – useful for delicate ingredients. A typical lower pressure is 8 psi or 0.533 atmospheres. Some models offer three levels of pressure: 15 psi, 10 psi and 5 psi.
4 SPARES. The main fabric of a pressure cooker will last for years, provided you take reasonable care. But every now and then you will find yourself needing to buy spares. The most frequent requirement will be for the silicone/rubber seal that seals the lid to the body of the pan and makes the pressurizing possible. A faulty or weakened seal means that proper pressure is no longer possible. Other spares you may need include the spring in the valve (or weights) and overpressure blow-out devices. The reason for putting availability of spares so high up the features list is this: if you are tempted to buy a no-name cooker, or acquire one from abroad – by mail order or on holiday – you may find that spares are difficult or very expensive to obtain. Before making a purchase, carry out an online search on your preferred cooker and then add the word “spares” to check ease of availability.
5 ACCESSORIES. The manufacturers of the least-expensive pressure cookers sometimes omit essential accessories such as a trivet and basket. Check carefully what is included and the prices of any additional items.
Electric pressure cookers have proved very popular in some parts of the world and are almost unattainable elsewhere. It is certainly puzzling that where I live, in the UK, very few models are available unless by overseas mail order. Yet my fellow citizens seem to love all manner of strange cooking gadgets – bizarre combinations of bread toasters and egg cookers, blenders with heating elements, chocolate fountains.
The first generation of electric pressure cooker didn’t offer much benefit other than to those with very small kitchens and limited cooking facilities. They were like stove-top pressure cookers except that there was a heating element inside. Some of them also included a mechanical timer to switch the device off at the end of cooking time, but you still had to wait until full pressure was achieved before starting the timer. In later models, the mechanical timer was replaced with a digital timer but also with the same defects in that you had to start it manually once full pressure had been reached.
Advantages
There are, however, significant benefits from the current generation of electric pressure cookers – sometimes labelled “smart” – as they combine internal sensors for pressure and temperature with microprocessor control. The result is that the cooker can detect when it has reached full pressure and can then count down the actual cooking time. The electronics can also provide an additional layer against mistakes – trying to pressure cook at other than the “proper” pressure and turning the unit off if there is insufficient fluid in the base. In practice, most of the devices on the market are cleverer than that in that, like more expensive conventional and microwave cookers, they provide an electronic menu of food types and will perform the timing calculations for you. Most of them will also allow you to set a delayed start.
Some of these advanced electric pressure cookers can also function as slow cookers – after all, a slow cooker is simply a device that combines temperature control with a timer. Some are advertised as “multi-cookers” and have rice and congee (Chinese porridge) settings; these are rather popular in the Far East.
Disadvantages
But there are also a number of downsides – and not all of them are immediately obvious.
The first is slow depressurizing. At the end of cooking time, the inside of the pressure cooker has to return to normal atmospheric pressure and the temperature must drop. Most pressure cookers have a safety device stopping you from premature opening before pressure has been reduced.