"The kingdom of heaven is like yeast"?

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Is it just me or does it seem that fermentation is getting an awful lot of press lately? All of a sudden there are a whole lot of books on the subject of home fermenting and just this morning I sat down with the paper only to find a big article on the health benefits of bacteria, probiotics, and such fermented foods as yogurt (remember that post I wrote some months back?, apparently I was ahead of the game), sauerkraut, Korean kimchi, and stinky French cheese. You don’t have to convince me. If there’s one food group I love, it’s the fermented one. Apparently I’m not alone.

But how many of you know what fermentation actually is?

Here’s the biochemical definition: “a metabolic process whereby electrons released from nutrients are ultimately transferred to molecules obtained from the breakdown of those same nutrients.”

Still not too clear? Try the culinary definition. “The process of converting sugar to carbon dioxide and alcohol with yeast.” Fermentation, in other words, is when yeast digests sugar, giving off carbon dioxide and alcohol as waste products. Fermentation is why bread dough rises and grape juice turns into wine, not to mention why about a billion other everyday delicious culinary reactions take place.

Fermentation doesn’t sound nearly as appetizing, though, when it’s described as the process of allowing “certain microbes to degrade the original food, but not beyond the point of edibility.” These are the words of Harold McGee whose On Food and Cooking is a bible to lovers of kitchen chemistry Fermentation, he neatly concludes, “is essentially a process of limited, controlled spoilage.” Gee whiz. How good does that sound? Cheese as no more than spoiled milk and kimchi as nothing but rotten cabbage.

From my perspective as equal part foodie and academic (this blog isn’t called Academy of Food for nothing), I find the whole question of whether fermented foods are delicious or rancid very interesting. Flip back more than 2,000 years and you find that Jesus couldn’t make up his mind on the matter either. On the one hand, he likened the kingdom of heaven to yeast: “the kingdom of heaven is like yeast that a woman took and mixed in with three measures of flour until all of it was leavened” (Matthew 13:33). Truly yeast can be treasured as a pearl of great price. 

But in another passage, Jesus wasn’t so fond of the eukaryotic microorganism, as the chemists like to refer to it: “Beware the yeast of the Pharisees,” he warned, which was his way of calling them a bunch of gasbags not to be trusted. God, by the way, didn’t much care for leavening either and prohibited his people from offering it to him: “No grain offering that you bring to the Lord shall be made with leaven” (Leviticus 2:11).

So which is it? Airy, spiritual and able to lift your spirits (or at least your dough) or gassy, bloated, and hypocritical?

Or, to lurch back into the present world, when does a deliciously fermented cheese become a rancid glob stinking of ammonia and old gym socks?

When, one might wonder, does eating probiotics make one need to resort to antibiotics?