David
Speed isn’t everything
It is possible to achieve a high throughput with a small unit by making it run very fast, but with significant negative results. Never select a unit based on the maximum production rate but instead opt for one that can achieve double the desired production. Always opt for variable speed. The speed should be varied during production so that it is fast enough to knock off the berries whilst causing minimal damage to stems.
Drum and paddle design
The direction of rotation of the paddles and drum is also important. If they work in the opposite direction to each other, the shear force is high and stem damage is therefore inevitable. The best units have both rotating in the same direction, with the paddles faster than the drum. The cheapest way of producing a drum is to laser cut stainless or punch out the holes. But this can leave sharp edges. These will act as knives,
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cutting any stems that poke through. Whilst these can be smoothed off, a plastic cage is much gentler. Berry size varies from variety to variety and the cage should take this into account. One option is gradation of hole size down the length of the drum. The other is to have more than one drum, with one for large berry varieties (such as Seyval Blanc). Paddles can also be made simply out of cut stainless steel. But the optimum is rubber coated ‘fingers’ where the pitch can be adjusted. This affects the angle the bunch is hit and the rate at which it progresses down the cage. Giving another possible adjustment for the process. Ease of cleaning is essential. It should be simple to remove both the cage and paddles so that cleaning can be done quickly and efficiently. If not thoroughly cleaned of all grape residue at the end of each day, a de-stemmer will quickly become a source of infection of acetobacter. For a perfect result opt for secondary selector. These units use a series of rotating disks that allow berries to fall through but any remaining stem fragments get separated out. For machine harvested fruit, one of these on their own will suffice in place of a de-stemmer.
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At first glance, the function of a de-stemmer/ crusher would appear very simple: separate berries from stalks without damage to either and lightly burst the berry to aid juice extraction. However, the pitfalls of doing this badly can have a significant negative effect on wine quality. In particular damage to stems will result in excess astringency and bitterness, as will the crushing of seeds. The equipment that is available varies wildly in its design and this article discusses some important considerations.
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Crusher options
There are fewer pitfalls in the selection of a crusher. The rollers should be rubber coated (as 99% on the market are) and with a gap that can easily be adjusted to suit the berry size. The aim being to just burst the berry and not flatten it. And of course, cleaning should be easy.
www.bevtech.co.uk David Cowderoy 01444 411141 / 07400 208205 paper-plane david@bevtech.co.uk
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