Zinc can be deficient even in all-malt worts, because most of it tends to be lost during lautering. Extra zinc can be added in mineral form (ZnSO4 or ZnCl2), or it can be incorporated in a nutritional product.
To get around the law, German brewers would incorporate zinc plumbing fittings in their breweries, or add zinc chains to the rakes or simply add live yeast to the boil kettle.
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