primary fermentation of grape must can be performed in rectangular vessels , such as conventional fruit picking bins , while providing a comparable surface area to volume ratio of toasted or plain oak to barrel fermentation . the oak or any other wood is provided in the form of planks that are supported in a stacked and spaced apart arrangement in a supporting frame that sits within the bin . the frame and oak can be removed together when sufficient oak flavor has been extracted or before pressing the juice from the must to complete secondary fermentation . the wood and or frame can also provide a means to submerse the cap that forms in primary fermentation .