Why It Whips

• Plain milk can be whisked or frothed to a foam, but it's fragile and deflates in minutes. Heavy cream is different; it can make a long-lasting, stable foam because of its high fat content. Ordinarily, the fat in cream holds together tightly in rounded globules, like a microscopic version of the droplets of fat you see floating on your chicken soup. The force of your whisk shearing through the cream breaks up those tiny globules, which trap the cream's moisture as they attempt to rejoin with other fats. As you continue whisking, the cream forms a light, stable structure of bubbles that holds its shape.

Cold and Stability

• Much of the foam's structure and stability comes from cold. Every chef and baker knows that cold cream whips more reliably and holds its shape better, though many don't understand why. The fat in cream is exactly the same as the fat in butter, and it holds its shape best when cold. When butter reaches room temperature, it begins to soften and sag. The same holds true for whipped cream, which retains its appearance only until its fat warms enough to lose its shape. Then the fat globules melt and run together, freeing the milky portion of the cream. The foam rapidly deflates, melting and pooling on your dessert or in your mixing bowl.

Ordinary Life Span

• How long whipped cream lasts once it's at room temperature is variable, but it's not long. If the surroundings are hot and humid, it can begin to visibly deflate and lose its texture in an hour or less. In cooler climates, or in a space that's well air-conditioned, a garnished dessert can last for two hours or longer. Under refrigeration, whipped cream deflates more slowly. It can be whipped one day and used the next, or desserts can be garnished and then held under refrigeration for the next day. After the first day, the cream begins to deflate and develop an ivory hue, rather than the pure white it displayed initially.

Stabilizers

• For whipped cream that holds shape longer under refrigeration, or withstands room temperatures longer without wilting, home and professional bakers use a variety of stabilizers. Commercial bakeries rely on stabilizers made from starches and natural gums, which can keep the cream usable for three to four days. Unflavored gelatin can be melted and whisked into the cream, lending it good stability for up to three days in refrigeration. It must be used while still soft for the best appearance. For kids' birthdays and other home events, whipping instant vanilla pudding into the cream can make it durable enough for a hot summer's day. It gives the cream a yellow tinge and a distinct flavor but is effective.