Question: I am a senior citizen who has been cooking and baking for a number of years. What is the difference between active dry yeast, rapid rise yeast and bread machine yeast? I thought all yeast was the same. — Jean H. M., via e-mail

Answer: Like you, I am also well into my senior years at 79 and commend you for still being a cook and a baker. In one sense you are right; all yeast are unicellular living organisms, among the most numerous in nature.

But for our purpose, there are two basic kinds — the baker’s yeast and the brewer’s yeast — the first designed to make bread-flour dough rise, and the second to aid the fermentation in beer and wine. They are not interchangeable; brewer’s yeast won’t make your loaf light and airy.

Although yeast has been used for both purposes from times immemorial, we didn’t really understand how this magical, microscopic fungus worked; bakers and brewers had to depend on transient airborne strains of the fungi, from which they often nursed their own colonies.

It was not until Louis Pasteur cracked the code on fermentation, in the 1850s, that scientists were able to “cultivate” yeast. And it wasn’t until another quarter century later that Charles Fleischmann produced the first commercial yeast in the United States.

Fleischmann also pioneered the manufacture of dried granular yeast during World War II. It freed bakers from dependence of fresh cake yeast, which needed refrigeration and had a very short shelf life. Cake yeast is now all but extinct and even a “senior” like you didn’t remember it in requiem.

Old-fashioned starter dough is of course one line of fresh yeast that some dedicated bakers still nourish as one would a pet.

Active dry yeast is the umbrella group of all three varieties you asked about. It is called “active” because the yeast organisms are in a dormant state, but not dead.

As you proof the yeast, warm water and a pinch of sugar, kick start them awake — millions of them — and they begin to eat and produce carbon dioxide bubbles to aerate the dough. Oven heat expands and sets the tiny bubbles into the bread texture.

Rapid-rise yeast is a kind of fine-granule active dry yeast that carries a more powerful punch and makes the dough rise twice as fast as the regular.
It has some additional advantages: It does not need to be proofed, it can be mixed with the flour and other dry ingredients before the liquid is added, and generally need just a single rising.

Bread machine yeast is really the same, except that some marketers are touting its robust nature, able to withstand the rough and tumble of machine handling.

For all kinds of active yeast, read the expiration date on the package and discard if too old. Inactive yeast is also used as a nutritional supplement as well as in preparing extracts, such as Marmite.

Q. I have a kidney problem resulting from an injury so I have to keep careful track of what I am eating. I am having problem finding a book that gives me information about the nutrients in what I am having. Can you suggest some books? — Eleanor R., Wellington

A. Your best bet would be to go to the public library near you and look through the numerous books they have on nutrition.
You should also talk to the reference librarian, who would know not only about the books they have on the premises but also about helpful books in the library system and even outside it.

Since you have a medical problem, you should also consult a registered dietitian, who can prepare a list for you and guide you through a book selection. Buy one or two books that you have thus narrow down to.

I have found two books helpful — The Nutrition Bible, by Jean Anderson and Barbara Deskins (William Morrow), and The American Dietetic Association’s Complete Food & Nutrition Guide, by Roberta Larson Duyff (Chronimed Publishing). Also, there is a wealth of information available on the Internet, although you need to be a bit choosy.

NOTES FROM MY KITCHEN: TRIMMING SUGAR IN FOODS