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The Crabtree Effect


In a previous life as an environmental specialist at a Tacoma, Washington firm I was known for my impulsive ways, in fact, my boss told me once that the way of Chuck is to “Leap, Look, and Land”, because knowing where I was going to land was not a precursor to me taking action. Although he meant it as a negative, I have twisted it into a positive by convincing myself that I am a man of action. I think that convinced no one but myself. Although I have tried to mitigate that tendency over the years, it still pops up at times in the brewery (rarely I think, but Butters and Father Bert think it is often). Apparently, it is often enough that they have given it a term, a “Chuck Up” (just one of the disadvantages of having a name that ends with “uck”). I would prefer the term, “Crabtree Effect”, but apparently, it does not have the same societal connotation, so I am reserving the term for something more positive, although I am doubtful it will stick.

Having said all that, that is not the Crabtree Effect I will be discussing here. I want to share some thoughts on the phenomenon known as The Crabtree Effect as it relates to yeast metabolism. The Crabtree Effect was first described by an English biochemist named Herbert Grace Crabtree. As a brewer with the last name Crabtree I feel obliged, even driven to better understand this twist of metabolic rules, this deviation from the norm that so openly carries my namesake.

Let us first make sure we are all on the same page in terms of traditional thought as it relates to yeast metabolism, more specifically Saccharomyces cerevisiae (the species used to make beer). S. cerevisiae are facultative anaerobes (some texts use the term facultative aerobe), meaning they prefer to metabolize sugar in the presence of oxygen (aerobic) but they can also do it in the absence of oxygen (anaerobic). So, traditional yeast metabolic thought goes something like this:

When yeast is introduced to a sugar mixture in the presence of oxygen, the yeast consumes the sugar and produces CO2 and water. During this phase, the oxygen in the solution is used up. Once the oxygen is depleted, the yeast switch to anaerobic metabolism and begin producing CO2 and ethanol.

That’s it. Simple. One question that pops up is, “Why do they prefer to use oxygen?”. The answer is also simple. More energy is derived by metabolizing sugar in the presence of oxygen than in the absence of oxygen, much more. It is simply good biological economics. Why would the yeast spend $10 to get $15 worth of fuel when they could spend $10 and get $100 worth of fuel? Who would?

The Crabtree Effect turns this traditional line of thinking on its end. Essentially what it says is when there is an abundance of sugar in a solution, even in the presence of oxygen, yeast may utilize sugar less efficiently (anaerobic) than they could. In other words, yeast will begin to produce CO2 and ethanol even before the oxygen is depleted. Why would they do this when they could be getting far more energy from another method (aerobic)? Again, the answer is simple…. because they can. In the presence of ample resources, efficiency is apparently not needed. This is of course an oversimplification of the process (minus the ATP regulatory control, ADP, Delta G’, and kcal. mol-1) and is far less anthropomorphic than I am stating, but you get the point.

In my research into the Crabtree Effect I have come to 2 conclusions. The first of which is how this impacts brewery operations. I fear this discussion would be interesting only for those of you immersed in the science of brewing and would be full of brew talk that would be more appropriate among brewers over a pint. So I will skip to the second conclusion which is more contemplative, less scientific and, honestly, more interesting for the non-brewer. Having a background and love for biology, I have always been interested in the life lessons that biological systems and processes can teach us, and the Crabtree Effect is no exception. So, I go back to the question of why yeast would not use the most efficient metabolic process available to them. The answer was, “because they can“. This is not an attempt at sarcasm, but more of a factual observation that is inextricably tied to our own experiences and behaviors as human beings. In the presence of ample resources we, as human beings, are notorious for not being efficient with our resources. Why? Because we do not have to be efficient. We see it every day in our society. We buy prepared foods when it would be more efficient to prepare them ourselves. We drive SUVs rather than smart cars to go the same distance. We live in 2,000 sq.ft. homes when a 1,500 sq.ft. home would suffice (or 200 sq.ft. for you tiny house folks). Please know that I am not judging anyone. I am as guilty as the next person (and I use the word “guilt” very loosely). But the fact remains, that most of us are not efficient consumers of our own resources. Now, one could effectively argue that, when it comes to business, what appears to be inefficient is actually more efficient (e.g. saving time so you can be more productive). That might be true is some cases, but not in most. In reality, our inefficiency is more often tied to our perception of being more comfortable or making our lives easier.

So, what is the lesson here? Honestly, I don’t really know. I just thought the parallels were interesting. You are probably thinking that I’m taking the comparison too far. Well…maybe I am. But the comparison has me thinking that I should plan my landing before I leap. Because leaping first may not be the most efficient use of my resources to get to where I really want to land. I guess that is it. Look! Leap! Land! In that order. If you take away nothing from my musings here, other than this, then I will have succeeded (at least in my own mind) in putting a positive twist on the term, The Crabtree Effect.

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