Forecasting of purchasing quantity of Manalagi apple for apple juice drink production in PT XYZ Malang

Batu City is a city with abundant agricultural and fruit commodities, in particular apple. Apple juice drink is a fruit juice drink prepared from apples with the addition of sugar and citric acid. One producer of apple cider in Batu City is PT XYZ. The effectiveness of the production process in a company has strongly related to the needs of raw materials. The planning activity for raw material requirements can be applied if future sales projections have been obtained. In this case, forecasting demand needs to be done. This study aimed to forecast the quantity of purchasing Manalagi apple as the main raw material in apple juice drink production process. Historical data of Manalagi apple purchased from January 2016 to December 2018 was used. The forecasting study was carried out for the period of January to December 2019. From the time series plot, it was found that the data for purchasing raw materials for apples was seasonal. Then, the purchasing data of the Manalagi apple was transformed twice to fulfill stationary assumptions. The best Seasonal Autoregressive Integrated Moving Average (SARIMA) model obtained was (1,1,0) (1,1,1)² with the Mean Square Error (MSE) of 0.0106901. The model showed that the average of apple's purchasing in 2019 was 9786.1 kg/month, with the highest and the lowest value 87950.2 kg (in June) and 249.3 kg (in January), respectively.