Can you make arbitrary food out of yeast?

Question

In his Robot Series, Isaac Asimov mentions "yeast substitutes" as a way of creating enough food to feed everybody in the Cities. It's also mentioned in Prelude to Foundation. Here's a few quotes from The Caves of Steel:

• City culture meant optimum distribution of food, increasing utilization of yeasts and hydroponics.

• A fork and two slices of whole yeast bread appeared[...]

• Human beings had grown used to yeast substitutes, but animals, more conservative in their way, insisted on real grain.

• [...] yeast-nut cake and a rather extravagant slice of fried chicken on cracker

• Uncle Boris always had a little supply of yeast delectables: small cookies, chocolaty things filled with sweet liquid[...].

• Beginning with the mountains of wood and coarse cellulose that were dragged into the City from the tangled forests of the Alleghenies, through the vats of acid that hydrolyzed it to glucose, the carloads of niter and phosphate rock that were the most important additives, down to the jars of organics supplied by the chemical laboratories—it all came to only one thing, yeast and more yeast.

• "When New Yorkers started getting strawberries out of season a couple of years back, those weren't strawberries, fella. Those were a special high-sugar yeast culture with true-bred color and just a dash of flavor additive."

My knowledge of yeast is pretty basic: you put it in dough to make bread rise and you put it in water to make beer. I understand there are also other uses for it, but I've never heard of "whole yeast bread", "yeast delectables" or "those weren't strawberries, fella."

There's even zymoveal and protoveg, which, I would guess, are meat and vegetable substitutes made from yeast:

As it is, zymoveal and protoveg are very good. They're wellbalanced nourishment with no waste and, as a matter of fact, they're full of vitamins and minerals and everything anyone needs[...]

Is this realistic or is it something Asimov invented?

Answer 1

yes

Or at least close substitute that would require a bit of flavoring etc. But that's what was described in a book anyway.

But not yeast as we know it. For hydroponics, you need organism that can feed by photosynthesis. Attempts to make photosynthesing yeast was made in 2006 and other times and places.

Perhaps more challenging is the idea of transferring plastids to a non-plastid-bearing host. Such a feat was attempted by several investigators 30 to 40 years ago (Rumpho et al., 2006), but developments in model systems and biotechnology make this potentially more feasible now. What does it take to begin charting this territory? First, a suitable host is needed. Yeast (Saccharomyces cerevisiae) would be an obvious first choice because of the availability of yeast artificial chromosomes that can carry the large amounts of genetic information that might be required for establishing a functional plastid in a foreign host. Since most proteins needed for plastid function are not encoded by the organelle, transferring large numbers of plant or algal genes to the synthetic host, many of which would encode plastid-targeted proteins, would no doubt be required to provide the plastid in its novel environment with the proteins it needs to survive and function.

Source

This means that at least some scientists believe photosynthesis in yeast can be possible, and yeast is a well known organism with available synthetic chromosomes to add arbitrary genes. Yeast are well known and already used as a host for protein production.

So we have main points:

• It might be possible to make yeast with photosynthesis - sugars
• It is possible to force yeast to produce protein we want - protein
• Under right conditions, yeast produce fat
• Yeast are good source of many vitamins

With vitamins, sugars, protein, and fat the rest is just mixing, texturing and flavoring, just like Asimov predicted.