Wednesday, July 22, 2020

Refrigeration in the Early Bronze Age

Via Volkstimme:  "Prähistorischer Kühlschrank"

Archaeologists have discovered a "refrigerator" among the houses surrounding the German Stonehenge.  Ringheiligtum Pömmelte was originally built by Beakers and continued without break into the Aunjetitzer or Unetice Culture.  The refrigerator (big pot in a deep shaft) was probably from this second phase.  (I believe it is clear that the shaft is not a well)

(This is an aerial video of the enclosure, first of a series)

The news of this discovery stirred some lingering questions I've had about the Beaker homestead and daily life, being that it was a dairy culture and the logistical problems of food preservation.  As Victor Mair mentions in his blog post "Galatic Glimmers", fermentation of milk into something like kumis is likely how steppe peoples and Beakers would have partaken.  Since Steppe folks were seasonal movers, refrigeration in wells or pits may not have been a worthwhile effort.  Plus, lactase persistence appears to have been much less common than in modern Europeans, so fermentation must have played a big role in consumption.  

As these people intermingled and settled in Northern Europe and around the snow-capped mountains further south, keeping raw milk products for longer periods of time became viable.  With that, the need to process milk may have been reduced while changing consumption habits.

So as a background, it may be surprising to know that refrigeration has been around for quite awhile.  In this case, quite a while.  There's about three methods ancient people used to refrigerate food or keep ice.  Evaporative cooling has been around since at least the Bronze Age (Yakhchals, Zeer Pots, Chinese Jian fridge).  Unsurprisingly, this method is more conducive to warm climates where evaporation is faster.

As a side funny, See Jian's high-tech $14,000 fridge:

Subterranean spaces and heavily-insulated ice rooms seem to have worked in much of Europe where the climate is cool enough.  In fact, there are other examples of cold storage from Beaker arrangements in Europe, such as these 'larders' of Oban, Argyll.  (and later discoveries Swiss pits, Pass-me-a-cold-one)
Cooling milk, yoghurt or beer may have been as simple as chilling pots in lake water or a well.  

A lot of European food was preserved by smoking, salting, brining/pickling and fermenting.  At least in the Isles and Far North of Europe, preserving butter was done in bogs, which sounds gross but actually produces good results.  So good, that a lot of these Bronze Age butters are still being found, some from the Beaker period.

Refrigeration techniques shouldn't be too surprising, but how common was it, and how might have it changed milk consumption?


  1. If it is a cooling pit for food c. 2,000 BC, this seems by far the earliest of the examples mentioned here (only the Argyll pit c. 1,000 BC gets near it).

    Not sure about Steppe folks as movers morphing into settled Beakers. I'm often told that R1a & R1b Steppe lineages and Steppe DNA remained rooted to the Steppe for thousands of years and didn't leak out until in a flood with Corded Ware and Bell Beaker; whereas Beakers appear to have travelled (rather than settled) more than anyone else.

    Saxonic Unetice is interesting though, as autosomally it looks pretty much like core NW European Beaker settling down. As lactase persistence seems only really to have expanded from the second millennium BC, and particularly across Northern Germany, the Low Countries and Britain/Ireland, I suspect you could be onto something by suggesting that it might have been cooling pits developed in North Western Beaker that changed milk consumption.

  2. I've examined Unetice DNA from that part of Germany, which is relatively straightforward to read.
    It looks to be substantially North West European Beaker people, overlain with some Ukrainian I2 paternal lineages (Yamnayan and non-Yamnayan).

    The question is - would refrigeration pits have been Beaker community innovations, or imposed on Beaker women by alpha males from Ukraine?

    1. I'll assume that refrigerating food and grain was already practiced in the Neolithic by Neolithic Europeans. I think the biggest change is not so much a change in technology or know-how, but a change in settlement habits, from an intensive dairy-herding culture living in wagons to a much more domiciled way of life, living probably in many of the already existing farming hamlets. Having a permanent residence enables the occupant to make those improvements, such as digging cellars and shafts. So storing milk and not having to process it is where I think the big change happens.

    2. Do we know whether there is any evidence of refrigeration pits in the Neolithic? Aren't storage pits per se seen as particularly characteristic of Unetice settlements?

      Only one Unetice sample (I0164) had lactase persistence, as far as I am aware, and would presumably have had an advantage in a strongly milk-drinking culture. It is perhaps not entirely a coincidence that I0164's non-standard autosomal profile provides the closest match for the Central European aDNA that we see proliferating in samples further West later in the Bronze Age.

    3. I really don't know the extent to which Neolithic settlements would have done this other than to say that permanent, sedentary life might have allowed for more elaborate subterranean structures like wells, storage pits, cellars, etc.

  3. Yes, the extent to which food storage pits were utilised in the relatively sedentary Neolithic period or the Beaker era is unclear, but it does seem clear that storage pits were a central feature (large and numerous) in the Unetice Bronze Age. As you suggest, this might have allowed people to store and consume unfermented milk for much longer, catalysing significant dietary change.

    This seems to run pretty much in parallel with the exponential growth in lactase persistence, of which there is little or no sign in Neolithic Europe, Yamnaya, Corded Ware, Bell Beaker or even the early Bronze Age; but by the end of the Bronze Age, it appears to be in the majority.

    Effectively, systematic milk storage might have led to a hidden population replacement in Northern Europe no less significant than the replacement of male lineages in the preceding millennium. Those who couldn't tolerate the raw milk very well might have struggled with poorer health, whereas those could tolerate it might have thrived.

  4. There is a paucity of data, but two out of four Unetice samples with lactase persistence readings (RISE431 and I0164) are LP positive; and the two samples which are LP negative both have non-local (Ukrainian) yDNA lineages. Additionally, Rathlin 1 (which has a Unetice-like aDNA profile) is one of the very few early Western samples to be LP positive. Large food storage pits, lactase persistence and Unetice aDNA do perhaps appear to go hand in hand.

    Samples bearing this kind of profile (EHG-heavy, but with relatively minor CHG) are almost exclusively female. My suspicion is that the Bronze Age population replacements in Western Europe were a bit of a rarity, being predominantly female-led and with dairy food as the catalyst. This would perhaps help explain how paternal R1b Beaker lineages remained the same, while culture changed around them.

    1. @ Nicolas Paul

      Correct me if I'm wrong but was Rathlin not part of the Bell Beaker Culture which precedes the Unetice Culture ? So does the Geneflow not rather point from West to East at that point in time when Unetice formed ?

  5. I've run some autosmal analyses, which seem to support a hypothesis that expansive migrations of Unetice food pit people were significant in the replacements of non-LP populations by LP-populations during the Bronze Age. These appear to have occurred just after Bell Beaker and had a minimal impact on its R1b paternal lineages, matching that the vast majority of the early samples with this profile are female.

    My own calculations estimate the following contributions from Unetice -
    Poland & Czech Republic (modern) - 75-85%
    Sweden (late Bronze Age) - 48%
    Sweden (modern) - 55%
    Ireland (Bronze Age Rathlin 1) - 57%
    Germany & Britain (modern) - 15-25%
    Spain Castille (Bronze Age) - 27%
    Northern Spain (modern) - 20%

    Published admixtures from Olaide demonstrate something similar - EHG-heavy/CHG-light additions to British DNA during the Bronze Age, and similar population replacements in Iberia c. 1,800 BC.

  6. The book : Las sepulturas campaniformes de Humanejos (Parla, Madrid) is available here:

  7. and the web site about Camino de las Yeseras here:

  8. When I was growing up my parents used a root cellar which basically took advantage of the cooler underground temperature relative to surface temperatures in the summer. But that only gets you down to the mid-60s in ºF. It won't keep dairy cold for long.

    Northern Europe is a lot further north than many people realize in terms of latitude and there aren't many places in Europe where you can't manage without AC in the hottest months. It was also historically more forested with mitigated extreme highs and lows.

    But this is the first I've seen of icebox oriented structures in this era in Europe (also featured in the animated movie series "Frozen", further north climatewise). I wonder if they insulated with sawdust at all as ice houses used to.