Washing powder, coffee and milk have been identified as the major contributors to price increases in stores since the beginning of the year, trade union Solidarity said on Sunday.

"Omo washing powder, Ricoffy coffee and Clover full cream milk have been the big outliers with regard to price increases," said union spokesman Jaco Kleynhans in a statement.

"The price of Omo increased by an average of R10,20 (21.1 percent), while Ricoffy and Clover milk increased by an average of R6,66 (14.5 percent) and R3,36 (19.3 percent) respectively."

They had been the main contributors to an average increase of 5.5 percent of a basket of goods at Spar, Pick n Pay and Checkers monitored by Solidarity over the last four months.

The food basket Solidarity had been keeping an eye on consisted of 25 products. It included Albany white and brown bread, Clover full cream milk, Flora cooking oil, Stork margarine, Selati sugar, Tastic rice, Fatti's and Moni's macaroni, Impala maize meal, Ricoffy coffee and Omo washing powder. Products on special offer were excluded.

"In April the food basket at Spar cost R7.95 (3.10 percent) more, at Pick 'n Pay R19.75 (8.2 percent) more and at Checkers R12.80 (5.1 percent) more than in January this year.

"Pick 'n Pay still remains the cheapest shop for this specific basket, followed by Checkers and Spar."

The price of two products in the basket actually went down at all supermarkets over the last four months. Stork margarine went down by an average of R5.24 (5.95 percent) and Impala maize meal went down by R2.40 (7.9 percent).