Peaty tales of a peat freak

I used to work with peatlands. “Wait, what?” is the normal reaction I get when I start with this sentence. And the second reaction is usually: “Why did you work with peat?”

Now, I could start with a long (and probably boring, to some) tale about the fundamental role that peatlands had and still have in the global carbon cycle (and therefore the role they play in the climate system) and why they are amazingly important ecosystems, but I’ll wait. For now. Meanwhile, I’ll try to focus on what the hell is peat and how is it used in whisky production.

What the hell is peat?

IMG_3092
Peat drill. It’s used to drill peat at different depths At boreal latitudes, peat normally grows at a 1mm/year rate. Therefore, if we are looking at a piece of peat extracted at, say, 6.5m (like the one in the photo), we’re looking at the residues of vegetation from some 6500 years ago!

Well, peat is essentially partially decomposed organic matter. Sounds tasty right? What happens is that, because of the low temperature and/or the high humidity conditions in these ecosystems, the organic matter is decomposed slowly and not so effectively. Moreover, a typical kind of vegetation you’ll find in boreal peatlands consists of peat mosses (usually different varieties of Sphagnum mosses), which adapted to live in these water-saturated conditions and which decompose more slowly than other vegetation types. Therefore, the annual deposition rate (the organic matter that accumulates) is larger than the annual decomposition rate. Repeat this process for some thousands of years, say after the last glaciation till today, and you’ll end up with our beloved peatlands, with peat beds up to 10m deep. Nowadays peatlands cover about 3% of Earth’s land surface. Does it sound negligible to you? Well, think about the fact that if you put together all urbanised areas in the world, the total sum amounted to about 0.5% of Earth’s land surface in 2009 (Schneider et al., 2009)! What a mountain of peat!

And how is it used in whisky production?

Probably this one is the most interesting part for you all malt maniacs. The so-called “peaty flavour” that characterises, for example, some Islay whiskies, comes from the drying process used to stop the germination in the malted barley, a process called kilning. Germination needs water to transform starch into simpler sugars, those sugars that the yeasts are going to banquet with during the fermentation process. Some distilleries use peat fires to dry the malted barley, and the “smoked” smell derives from the phenols and other aromatic compounds produced by the combustion of peat, which get absorbed by the barley during this process. The famed “ppm count” appearing on some bottles refers to the phenolic parts per millions measured at this point, after the kilning, therefore before distillation, ageing and all the other processes that can definitely affect how much of a “smoky flavour” the whisky has.

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Did anybody put some E150 in the water? Hahaha…

I always find it kind of funny to read (or hear) that the water used in the distillery to wash the barley to extract the sugars comes from a peatland and therefore it infuses some “peaty” flavours to it. Sadly, this misconception is repeated also by some tour guides in the distilleries, and I say sadly because this one is clearly a hoax. I mean, it’s true that water can get more acidic by passing through peat (sphagnum-dominated ecosystems are relatively acidic), and it can also become richer in some elements, as you can tell by the reddish colour of the carbon-loaded water stream passing through a peatland in Sweden in the picture above. All is well and interesting, but peaty flavour? Come on… So, to sum it up, these passages are really the only ones in which peat influences the whisky.

Are there really differences in peat sites?

The short answer is… YES! Peat is simply the result of the decomposition and deposition of organic matter on the soil, and its composition primarily depends on the kind of vegetation once living on the surface. Now, as I was saying, the main vegetation type living in peatlands are mosses. In some peatlands you can also find some remnants of older woody plants (kind of common, for example, in some Irish peatlands), and even nowadays there are some plants and shrubs surviving in these acidic and wet environments. Lignin is very resistant to decomposition and its presence/absence can be one of the biggest differences between Highlands and Orkney peat. On Orkney, humans arrived around 9000 years ago, and shortly afterwards they started with one of their favourite activities: deforestation. The issue here is that, because of strong winds transporting a lot of salt from the sea and the limited light due to the high latitude, the ecosystems could not recover quickly after these early anthropogenic blows. The small trees, without the protection of the bigger ones cut down by humans, also quickly became too exposed to the strong winds to survive. In fact, the Orkney Islands are nowadays almost treeless.

Different colours indicate different species of sphagnum moss.

Do all these processes influence the taste of the whisky? Well, probably, but it also might be that this influence is not as big as some distilleries want us to believe. The species composition in the ecosystem (and therefore their residues in the deeper peat strata) are not the only control on peat chemical composition. Large differences can be found between peat extracted at different depths, as it can be a factor even more important than the geographical location of the peatland, or the type of peatland (for the peat-maniacs, I’m talking about differences between bogs and fens, for example). The bacterial fauna is also very important, as it is the part of the ecosystem responsible for the decomposition, and it inevitably varies in each location (Harrison and Priest, 2009). On top of that, the temperature at which peat is burnt controls the kind of compounds created in the combustion: some “medicinal” notes come from higher combustion temperature and some “smoky” flavours from lower temperatures (everything is very well explained here). This looooong paragraph is just to highlight the fact that peat is not that simple. Yes, peat definitely differs from one location to another one, but it’s (almost) impossible to pin down some “flavour profile” found in a whisky to the geographic location where the peat comes from. It’s romantic, but it simply doesn’t work like that.

Just one more thing…

I know, I know, in a whisky blog blabbering about other topics can be punishable by death. But if I’m talking about peat I cannot avoid saying that, and it may come as a surprise for some of you, peatlands play a fundamental role in the global carbon cycle and in general in the global climate. They contributed to stabilise Earth’s climate, sequestrating carbon before it ended up in the atmosphere, in the oceans, or in Mordor. During the past millennia, they accumulated so much organic matter to become one of the largest carbon reservoirs. They contain over 550 Pg (petagrams, 1012 kg), which is quite a number (Yu et al., 2011)! Just think about the fact that the whole atmosphere contained about 590 Pg before we started to pump carbon in there like there is no tomorrow (now we have about 830 Pg of carbon stored in the atmosphere). The role of peatlands in the future is still subject of investigation, as we don’t really know how will they react to climate change. Will they release the carbon accumulated in the past because of accelerated decomposition rates (due to the higher temperatures), making our situation even worse? Or, as they did during the Holocene, will they keep accumulating carbon, acting as a kind of buffer for our crazy emissions? Only time will tell, now we should probably have a drink!

References:

Harrison B., Priest F.: Composition of peats in the preparation of malt for scotch whisky production. J. Agric. Food Chem. 2009.

Schneider A., Friedl M. A., and Potere D.: A new map of global urban extent from MODIS data, Environ. Res. Lett., 2009.

Yu, Z. C.: Holocene carbon flux histories of the world’s peatlands: Global carbon-cycle implications, Holocene, 2011.

3 thoughts on “Peaty tales of a peat freak

  1. “quel che succede è che il rateo annuale di deposizione (la materia organica che si accumula) è minore di quello di decomposizione (la materia organica che si dissolve)….” rileggo attentamente ma mi sembra un errore o sto andando per fragole in una torbiera?

    Like

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