Charring-induced morphological changes of Chinese "Five Grains": An experimental study

Area of Science:

• Archaeobotany
• Archaeological Science
• Paleoethnobotany

Background:

• Charring impacts seed preservation, limiting understanding of ancient crop assemblages.
• The "Five Grains" (wheat, foxtail millet, broomcorn millet, rice, soybean) are vital staple crops in Chinese history and common archaeological finds.

Purpose of the Study:

• To investigate how aerobic charring conditions affect the size, volume, and weight loss of key ancient grains.
• To provide data for minimizing preservation bias in quantitative archaeobotanical analysis.

Main Methods:

• Measured size and weight of untreated grains.
• Heated grains at various temperatures and exposure durations.
• Analyzed changes in size, volume, and weight.

Main Results:

• Grain size is directly influenced by temperature and exposure time.
• Most grains shrank at lower temperatures and expanded at higher temperatures.
• Soybean was least affected by charring, followed by wheat, rice, and millet.

Conclusions:

• Volume and weight can serve as conversion factors to correct for charring-induced preservation bias.
• Soybean, wheat, and rice show smaller volume variations.
• Further research on ancient samples is needed to explore other preservation factors.