I find leaf gelatine much easier to use than the powdered variety. It dissolves more evenly into warm liquids, rarely leaving blobs of pure gelatine lurking in the depths. Although it is not as widely available as the boxed sachets of powdered gelatine, it is by no means rare. I certainly think it is worth buying several packets whenever you come across it in delicatessens and specialist food and kitchen shops.
Of course, in most recipes the two are interchangeable – they are, after all, exactly the same substance, differing only in presentation. One exception is the Chicken in Jelly with Plums, where the leaves of gelatine are layered with chicken and plum, rather than dissolved into a liquid.
Wherever gelatine is used, the important measurement is the weight required, rather than number of sheets, or sachets, and even this may need to be increased by about one-third if, say, the weather is particularly warm, or the unmoulded jelly or terrine has to survive intact for some length of time in a warm room. Where you are adding the gelatine to a very thick base, such as mayonnaise, you can, conversely, use a smaller amount than usual. If you wish to make a plain fruit jelly, set and served in individual glasses with no need for unmoulding, you can get away with using 11 g/scant ½ oz to set 900 ml/1½ pints of juice.
Whether you use leaf or powdered gelatine, check the instructions on the packet before using. Leaves of gelatine are normally soaked in cold water for 15–20 minutes, until soft. It is important to drain them thoroughly, squeezing gently to get rid of excess water. Then they are ready to be stirred into the hot (but not boiling) liquid used in the recipe, making sure that they have completely dissolved before moving on to the next stage.
Powdered gelatine is usually sprinkled over 3–4 tablespoons of water in a small pan, then left to soak for 5 minutes. It is heated slowly without boiling, stirring until it has dissolved. It should be cooled if necessary, so that it is at about the same temperature as the liquid to which it is to be added.
It is worth noting that different brands of leaf gelatine may have different weights. Some sheets are longer or wider or thicker than others. The German brand I use is very thin, and dissolves quickly – there are six sheets to 11 g/scant ½ oz, enough to set 600 ml/1 pint of liquid. Other brands may be heavier, with only three or four sheets needed to set the same amount of liquid. Always check carefully before using.
The small sachets of powdered gelatine each contain 11–13 g/scant ½ oz gelatine (3 rounded teaspoons), again enough to set 600 ml/1 pint of liquid.
GELATINE CONVERSION CHART (All conversions are approximate)