WARNING: Wall of text ahead
Before I embark on an explanation of the evidence in support of my hypothesis, it occurs to me that I may have a more complete understanding of barley biology than the average person, and very likely the average brewer. Since my hypothesis stands in opposition to some long-held knowledge and handling practices regarding barley and brewing, I gathered it might be prudent to start by going over some information about the development of barley, and its interaction with the malting process.
The Australian government has an excellent publication providing a fairly thorough overview of barley biology – primarily from the applied perspective of its role as a cereal crop. You can access it here. The University of Minnesota Agricultural Extension also features a fairly in-depth article.
In summary: dormant barley seeds germinate after soaking up water (a process known as imbibition), and being exposed to the right environmental conditions (temperature, oxygen, and soil pH). The early stages of germination (which we exploit during malting) don’t last terribly long when attempting to grow barley; shoot emergence can occur as rapidly as 72 hours post-imbibition, though exact time varies with variety as well as environmental conditions. Seedling development time (the point at which green leafy material is evident) varies as well, but generally, the seedling emerges from the soil in 10 days to two weeks.
Following emergence, the plant grows and develops multiple stems (tillering), which then begin to elongate. Field barley can have anywhere from 2 – 5 tillers per plant. Not all tillers develop the flowering structure called a “spike” (colloquially called an ear), but this varies with strain. Many modern barleys have been bread to have a high rate of spike development.
The spike is the flowering part of the plant. It develops, and once it flowers (releasing barley pollen), the “fruit” of the barley plant – what we know as a “berry” or “seed” – begins developing.
Barley seeds generally reach full maturity ~25 to 30 days after flowering. During maturation, the grain develops, begins to develop and store starch, and gradually dessicates. Once the seed no longer yields to fingernail pressure, it is considered ripe for harvesting. Dried barley enters a dormant phase, and when properly stored, dormant seeds can last up to 18 months.
What follows is a relatively complex analysis of the biochemistry of barley development. If you’re interested, read on. If not, skip to the end for my summary.
[HEREIN LIES A BUNCH OF SCIENCE]
The dormant seed is where we start the malting process. The importance of malting barley for the production of beer is widely understood, and most people understand the story in the same way; that is, during malting, we slowly and evenly take the grains through the early stages of germination, to develop enzymes that we will later manipulate in brewing. Those enzymes include proteolytics, to denature the protein matrix (called hordeins in barley, and broadly lumped in with the gluten proteins) that contains the starch; alpha- and beta-amylases, which convert stored starch into fermentable sugars; and debranching enzymes, which help “chew” the starch up into chunks that the amylases can more easily handle.
I was under the impression – as are many brewers – that malting is absolutely essential in order to develop the enzymes necessary in order to convert the stored starch to sugar. That is, until I learned about barley maturation in more detail.
As it turns out, mature barley seeds contain some completely functional beta-amylase enzyme. The linked paper shows that roughly 40% of the beta-amylase content of resting barley can be recovered with a saline solution. A survey of other literature appears to indicate that alpha-amylase is synthesized during maturation, and is not present in dormant grains.
The remaining 60% of beta-amylase in barley is present in a “bound” form – that is, it is attached to a larger protein inhibitor. Sopanen hypothesizes that the inhibition is likely due to steric hindrance – a phenomenon in chemistry where reactions are slowed because of the actual size and conformation of the molecules involved. In other words, 60% of the beta-amylase in mature barley seeds exhibits attenuated activity because there’s stuff in the way of the active site.
The activity of so-called “bound” beta-amylase was thought to be latent; however, Sopanen demonstrates that the enzyme can be as much as 70% as active as “free” beta-amylase. However, it also appears to matter little; the “free” beta-amylase content of ungerminated barley is sufficiently to convert the entire starch content of the seed – if the starch molecules are made available to the amylases.
Alpha-amylases are also bound with endogenous inhibitors. In this case, the inhibitor reduces the activity of alpha-amylase by nearly 90%. This is likely important to barley maturation; it has been demonstrated that premature alpha-amylase production leads to a reduction in seed size and starch content. This makes sense – alpha-amylase has a greater rate of activity against larger starch molecules than does beta-amylase.
It has been known for some time that gibberellic acid plays a crucial role in barley metabolism. Work by JV Jacobsen (over many years) has led to an in-depth understanding of the role of gibberellic acid in barley; he started by demonstrating that the application of GA induced the production of multiple alpha-amylases, and went on to study the hormone extensively.
So, at first glance, it appears that germination is required for the production of gibberellic acid, which is needed for the production of alpha-amylase. But the barley kernel has sufficient beta-amylase to allow for conversion prior to germination. What’s the deal?
We have learned – thanks to advanced technology – that the maturing barley kernel prepares for germination while on the ear. It does so by switching to a sort of “preparation” mode, wherein it generates thousands of mRNA’s (messenger RNA’s, generated from genomic DNA and sent to the ribosome for translation into proteins) and stores them. In addition, the barley kernel generates and stores gibberellic acid precursors prior to full maturation.
The full sequence is actually quite complicated. Abscissic acid (ABA, produced during maturation) and gibberellic acid have antagonistic effects – that is, they each cancel each other. This creates the possibility of a biochemical “switch,” where the synthesis of one hormone takes over the other and changes gene expression. ABA is responsible for inhibiting alpha-amylase production; the synthesis of GA precursors prior to that is what enables the activation of the enzyme.
In fact, barley kernels generate mRNA’s for all sorts of proteins prior to dormancy – the full machinery for the resumption of transcription/translation duties is available in the dormant, un-germinated grain. Dessication of the grain halts the normal activity of the growing grain – in fact, the data from Sreenivasulu et al suggest that there is little effective separation between maturation and germination from a biochemical standpoint. The plant makes a smooth transition from one to the other. Dessication works as a “pause” function, and the plant prepares for this pause by storing mRNA transcripts – along with ribosomal proteins and RNA’s – that will allow for the resumption of development upon imbibition.
Most of the proteins required for the early stages of germination – those we need during malting – are not generated de novo from genomic transcription, but rather are synthesized from stored mRNA’s and ribosomal machinery. Some proteases are present, but more are produced during germination, along with ubiquitin (a universal enzyme cofactor found in all eukaryotes).
But the story these data tell is somewhat different than what is commonly understood; rather than germination being critical for the development of these enzymes, it is the existence of those enzymes (and their precursors) in the resting grain that allows germination to proceed at all.
[OK, DONE WITH SCIENCE]
So what does this mean for malting? Mature, un-germinated barley grains contain all the necessary mRNA transcripts, ribosomal machinery, and endogenous enzymes necessary to start and maintain germination. There is enough beta-amylase present in a mature barley grain to convert its entire starch content without further enzyme release. Why do we even need to malt barley in the first place?
It seems that the most critical stages in early germination are the production of gibberellic acid from stored mRNA, and the increased expression of proteolytic enzymes that degrade the protein matrix of the barley kernel. GA is a hormone that, among other things, removes inhibitors from alpha- and beta-amylases. The degredation of the protein matrix allows access to the starch in the kernel, which is converted by the amylases. Debranching enzymes are synthesized from stored mRNA’s during this time.
So it seems that some sort of time-centered processing is necessary in order to allow stored biochemical machinery to provide the grounds for the conversion of starch to sugar.
Does this have to be our modern method of malting? I don’t believe so. The presence of beta-amylase in those quantities indicates that the most critical need is the exposure of starch via the degredation of the protein matrix. You could accomplish this in other ways; you could, for example, perform an acid digestion of the barley, and then treat it with enzymes to convert the starches to sugars.
So again, why malt? It’s more efficient from an industrial standpoint – the division of labor means that someone else prepares the raw material for use by the brewer, who can then spend an hour mashing it to get the sugar. Alternate processing streams may affect grain flavor, or increase the total labor used to generate a beverage. Malting is a purposefully slow germination process, to allow for very even development of the grain; this ensures maximum yield from a barley harvest.
However, it doesn’t seem like that could be the only way to do it. There may exist an alternate system that allows for the generation of maltose from barley starch – but I’ll leave that for another time.