This article has been published jointly in both Chemistry in New Zealand and Chemistry in Australia. The article, “Milk on Ice”: A detailed analysis of Ernest Shackleton’s century-old whole milk powder in comparison with modern counterparts, was published in the March 2024 issue of the Journal of Dairy Science and is Open Access with Creative Commons Attribution.
Above: The tin-plated can of Defiance brand dried milk found in Shackleton’s Cape Royds base camp hut. Image: Antarctic Heritage Trust.
Dairy products are remarkable for their nutritional density. During the 20th (and into the 21st) century, milk and dairy products helped enhance public health for countries where they were readily available. A key part of milk and dairy product availability has been the improvements to both selective breeding of dairy cattle and farming practices. Yet one of the questions that sometimes arises is how we know whether the milk of today is as good as it was in our great-grandparents’ generation. The International Dairy Federation has provided expertise in dairy standards since 1903, and the Journal of Dairy Science has provided a repository for science knowledge about dairy products since 1917, but this knowledge doesn’t quite amount to a comparison.
As it happens, a single can of milk powder does exist that pre-dates all of the changes to cattle breeding, rumen ecology, farming practices and environmental conditions of the 20th century. This powder has been preserved in a dehydrated state that prevents bacterial degradation and in a frozen state that diminishes the rate of chemical deterioration. This historical artefact of inestimable scientific value was left behind from the 1908 Nimrod expedition at Shackleton’s hut at Cape Royds, Antarctica, and was rediscovered during restoration of the hut by the Antarctic Heritage Trust.
A sub-sample of this milk powder was collected on behalf of the Fonterra Research and Development Centre (FRDC) by the Antarctic Heritage Trust. Upon its arrival at FRDC’s laboratories, there was an enormous sense of relief when it was realised that the milk powder was still in a well-preserved state. It had been feared that the sample might have deteriorated over its long life into hard dark-brown lumps with a smell like putrefied cheese, so it was beyond our team’s most optimistic expectations to see slightly off-white and free-flowing granules that had only a relatively mild, milky aroma. It had also been feared that a deteriorated sample would not allow for more than the simplest compositional analysis, but as the analyses progressed in our laboratories it became clear that Shackleton milk powder had survived in a state that would still provide useful information. Along with the sense of relief at the fine condition of the sub-sample came a sense of responsibility to take great care in the stewardship of this powder, knowing that it was unique to science, and conscientiousness about its historical legacy as part of Ernest Shackleton’s heroic Antarctic expeditions.
Shackleton’s milk powder was made using a roller-drying process with subsequent milling, known to make powders that are granular and difficult to reconstitute in water. The modern spray-drying process produces fluffy, more easily reconstituted milk powders. (Milk components aren’t actually in solution but are better described as a charge-stabilised colloidal dispersion; hence milk powders are reconstituted rather than dissolved.) A gratifying aspect of this work is that the Defiance brand of milk powder was manufactured, probably in 1907, at a factory only 11 kilometres from where the FRDC is located in Palmerston North, New Zealand. Hence our comparative analysis of Shackleton’s milk powder with modern milk powders, published in the Journal of Dairy Science in March (https://doi.org/10.3168/jds.2023-23893), connects our farming and dairy science heritage (FRDC was known as the New Zealand Dairy Research Institute from 1927 to 2001) with modern dairy technologies.
Given the irreplaceability of the historical sample, it was necessary to consider carefully what testing approaches would yield the greatest value of information with the least amount of destructive testing. Whenever available, international standard test methods were used so that reliability of results could be assured. Where some destructive treatment was unavoidable, we used the smallest quantity possible that would still give reliable results and provide the largest number of different test results.
A question commonly asked is: what did the milk powder taste like? This isn’t an unrealistic question considering that, during the restoration of Shackleton’s hut, three cases of Mackinlay’s Rare Highland Malt whisky were rediscovered in a pristine state. Three bottles were sent to the Scotch Whisky Research Institute in Edinburgh, Scotland, for comprehensive chemical analysis as well as organoleptic assessment (https://doi.org/10.1002/j.2050-0416.2011.tb00455.x). Whyte & Mackay Ltd have recreated the whisky, which is now commercially available as Macklinlay’s Shakleton Blended Whisky, with a portion of the sale proceeds going to support the Antarctic Heritage Trust.
Tasting of milk (or any food) can be done in a manner that is scientifically robust, and FRDC has expertise in formal sensory evaluation of milk and dairy products that are both quantitative and repeatable. However, an approach such as quantitative descriptive analysis would have required a minimum of two litres of liquid milk, while four litres of liquid milk would be required for a full-flavour compound analysis to discover all of the potent aroma compounds (https://doi.org/10.1021/jf010334n). Both methods are destructive.
Rather than test for flavour, which inherently requires humans, we instead tested for volatile compounds using non-destructive testing. When compared to modern spray-dried milk powders, the volatile profile of Shackleton’s milk powder indicated that the milk powder was very much beyond its “best before date”. It contained a substantial quantity of compounds associated with both lipolytic (short-chain free fatty acids) and oxidative (aldehydes) off-flavours. Being roller-dried, Shackleton’s milk powder had a high proportion of free fat in comparison to spray-dried milk powder, and this would have made the fat content of the milk more susceptible to lipolysis and oxidation during storage, although the microbiological quality of the raw milk prior to manufacture of the powder is unknown and cannot be ruled out as a factor.
It is improbable Fonterra will ever market a recreated Shackleton’s milk powder in a similar way that Whyte & Mackay Ltd has recreated Mackinlay’s Shackleton Blended Whisky. In a neat historical connection, Antarctica New Zealand still provides the Antarctic Heritage Trust with Anchor brand milk powder for field trips in Antarctica.
The bulk composition of protein, fat, carbohydrate (lactose), major and trace minerals, and moisture and colour were all measured. The moisture content of Shackleton’s powder was higher than declared on the original label, probably due to the can having been opened and resealed early during its storage period. Expressed on a moisture-free basis, the composition was reasonably close to what was stated on the label.
When compared with modern spray-dried milk powder, it had lower lactose and higher fat, protein and ash content. These differences will be due to both fat and protein standardisation of modern commercial milk powders that give consistent dairy products without seasonal or lactational-stage variation experienced naturally during pasture-based milk production.
The major and trace mineral contents were similar, with the exception of elevated sodium, iron, lead and tin in Shackleton’s milk powder. We suspected the elevated sodium was due to the practice of adding sodium hydroxide to raise the pH of the milk before roller-drying (similar chloride levels to modern powder ruled out the addition of common salt.) The high iron, lead and tin contents of Shackleton’s milk powder could not have been due to environmental contamination, but most likely originated from the manufacturing equipment of the time, including water piping and especially packaging into tin-plated cans with lead-based solder seaming. Even though care was taken to sub-sample the powder from the can’s centre, jostling during the voyage to Antarctica may have abraded tinplate and solder, shifting contaminant metals toward the can’s centre.
The profile of amino acids was remarkably similar between Shackleton’s milk powder and modern milk powder, with the only real difference being the heat-labile lysine. The roller-drying process, diminishes this, and we found it was 20% lower in Shackleton’s milk powder. Shackleton’s powder was darker with more green and more yellow/blue hues than modern milk powders.
We wanted to determine which breed of cows were farmed 100 years ago, and how the proteins in their milk had changed during the intervening years. This would normally be done using κ-casein variant distribution from mass spectrometry of proteins but because of extensive lactosylation of the proteins in the aged Shackleton milk powder, renneting treatment was required to release casein-macropeptide fragments instead. It turned out that the ratio of A and B variant was 50:50, while for modern milk there was a 35:65 ratio. Therefore, Shackleton’s milk powder was probably made with milk from a Friesian/Holstein- dominant herd that had higher levels of κ-casein A variant, whereas Jersey cows typically have a ratio of 20:80 κ-casein A to B variants.
The fatty acid profile of the lipids from Shackleton’s milk powder was remarkably similar to current milk fat composition. This illustrates that the fat composition of milk has not significantly changed despite changes in breeding, rumen ecosystem and farming practices over that time. The relatively high C18:1 and C18:2, and lower levels of the shorter-chain fatty acids, suggested an early spring or late autumn milk from a Friesian-dominant herd (https://doi.org/10.3390/dairy3030043). This conclusion supports the findings from the protein work.
Little insight into microstructure was gained from a conventional light microscope, but transmission electron microscopy (10,000 x magnification) attributed to the poor solubility of roller-dried Shackleton milk powder was attributed to aggregation of fused casein particles that had large void areas from free fat. We were reminded of the comment by pioneering microscopist Miloslav Kaláb (https://doi.org/10.22443/rms.inf.1.55): “Examining milk with an optical microscope brings great disappointment since there is nothing to see except fat globules.”
The story of Shackleton’s milk powder hasn’t ended yet. As advances continue to be made in the sensitivity of scientific instrumentation and testing methodology, we expect there will be more areas for research that Shackleton’s milk powder can help address, such as research questions of food contamination from anthropogenic environmental pollutants released during the 20th and 21st centuries.
