[SunkenCiv]

Spoiler alert: Starch extraction started at least 30,000 years ago, based on residues from mortars/pestles etc. Just not from potatoes, at least, not in Europe.

[Pete from Shawnee Mission]

Probably something like Arrowroot. You find it in the shallows of european ponds. Its used for thickening soups or making cookies.

[ApplegateRanch]

Romans must have brought potatoes back with them, after dropping off loads of bricks for the Mexican/Central American temples. :-’)

https://www.science-frontiers.com/sf099/sf099a01.htm

[Red Badger]

The making of beer is a scientific exercise.......................

[AdmSmith]

It is a translation error by the journalist. In the article in English they wrote:
“What the experts discovered was a substance called miliacin, considered to be an indicator of millet. They also detected traces of different herbs and cooked potato starch.”

Here is the original in Czech: “Objevili i pozůstatky přidaných bylin a vaření škrobových zrn.” from this article

https://pardubice.rozhlas.cz/jedno-z-nejstarsich-bylinnych-piv-v-evrope-se-varilo-na-pardubicku-ukazal-8576362

The translation of this is “They also discovered the remains of added herbs and cooked starch grains.”

Most green plants store energy as starch, which is packed into semicrystalline granules.

The original paper

In 2017, a luxury bronze bucket was discovered near Kladina village in the Czech Republic. The bucket is dated to the ninth century BCE, and it is a unique artefact, having no parallel in Europe. Stylistically, it is a “transition type” dated between the Late Bronze Age (11th–10th century BCE) and the Hallstatt Period (eighth–sixth century BCE).

Detailed palynological analysis of verdigris and soil infill of the bucket identified a wide range of pollen grains belonging mainly to herbs, with bitter-sour properties, and cereals. Subsequent chemical analysis by gas chromatography/mass spectrometry of soil extracts revealed the presence of the compound miliacin that is a chemical marker of millet. Moreover, a starch analysis reveals the presence of enzymatically modified starch grains. These data, with the help of archaeological knowledge, indicate that the original content may have been millet-based food/beverage with addition of herbs. We suggest that this luxury vessel, given the contents we have identified, was deposited, in the late spring/summer months of the year.
https://onlinelibrary.wiley.com/doi/abs/10.1111/arcm.12711

Problem solved.