I believe Nepali Gundruk (silage popularly of brassica species e.g. radish and Chinese cabbage) making knowledge and conservation practice are relevant to share in this discussion.
1. Are there any lively examples of indigenous methods of food preparation and how do they influence food security and nutrition?
Formal published research will be welcome on this point. Gundruk making requires practices of fermentation and drying of moderately green leaves of the vegetables. The Nepalese farmers used to preparing and preserving the food item in the vegetable seasons, and eating in vegetable scarcity seasons. It contributes to nutrition not only by preserving nutrients but also by increasing taste by adding aroma. The product is rich in iron and very useful for reproductive women. The vegetable preservation method was popular and important in old days because farmers had limited or no access to green vegetables during off seasons. However, household importance of the food preservation practice has been declining with increasing production of green vegetable all round the year.
2. What informal strategies have been put in place by local communities to ensure that this knowledge is not lost?
Based on my knowledge, communities are not organized to ensure that this knowledge is not lost. However, the knowledge has been conserved in communities. Nowadays people accustomed to the taste of the Gundruk like to eat it even if they have enough access to green vegetable all round the year. People migrated overseas also like to eat the product. Even some children who have grown up overseas like to have its soup as they took up the taste for the product from their parents. However, some people do not know to produce the product overseas.
They ask parents, relatives or friends about the method of producing it. If they cannot produce themselves they ask family to send some as a gift for them. Nowadays the product carries a special Nepali identity. Thus some restaurants have included the soup of the product in their menu. Therefore if senior generation give some experience or taste of the product to new generations the local knowledge of producing or preparing is likely to pass informally to the next generation.
Thank you for reading my opinion.