The price of the Sinterklaas staple, the chocolate letter, has risen by 25% since last year because of failed harvests, inflation and a volatile market fed by speculation, the Financieele Dagblad reports.

The price of cocoa, which had held steady at around $3,000 per tonne for years, went up to $12,000 in April. It has since come down to $7,000.

Excessive rain caused by climate change and subsequent cocoa tree diseases have ravaged harvests in Ghana and Ivory Coast, which are the main producers, and, although the impact will not affect supermarket prices this year, chocolate letters are expected to be some 20% to 25% more expensive.

Higher fertiliser and pesticide prices have also depressed production while speculation is driving up cocoa prices. Increased demand from upcoming markets such as Asia is also boosting prices.

According to Rabobank financial analyst Julia Buech, the price hike could lead to smaller products containing less cocoa, or shrinkflation. “And that may include chocolate letters,” she told the Telegraaf.