DON’T—double Certo recipes. Better color and flavor and more certain results are obtained from single batches.
DO—use fully ripe fruit of the best possible color and flavor. Taste fruit, and if it lacks tartness, add the juice of 2 medium lemons (¼ cup) when adding sugar.
DO—prepare fruit exactly as the recipes direct. Do not simmer before crushing or squeezing unless recipes specify cooking. For crushing fruit, a food chopper is convenient.
DO—measure sugar and fruit exactly with the same standard ½-pint measuring cup, level full; or weigh both. A standard measuring cup holds ½ pint sugar (7 oz. by weight) or ½ pint fruit or juice (8 oz. by weight).
DO—use a large enough kettle so that your mixture has room enough to boil hard. A kettle of 6- to 8-quart capacity is recommended. If the 6-quart size is used for jam, add ¼ teaspoon butter with sugar to reduce foaming.
DON’T—confuse a gentle simmering boil with the full rolling boil specified in Certo recipes. A full rolling boil is a high, tumbling boil that cannot be stirred down.
DO—time the full rolling boil by the clock.
DO—stir and skim jams by turns for just 5 minutes before pouring. This slight cooling helps prevent floating fruit.
DON’T—expose jellies and jams to dust or dampness after they are made. Spoilage is caused by the growth of yeast and mold plants, which are usually carried by dust. Use clean glasses, new paraffin, and clean covers. Paraffin hot jelly and jam at once. Fill glasses only to within ½ inch of top. Store in a cool, dry place.
DON’T—judge the texture of your jellies or jams too hastily. Certo recipes are designed to give an ideal set at the time they are most apt to be used. Many grow progressively firmer for a week to a month after they are made.