What percentage by weight of oat and rice hulls should not be added?

The correct answer, indicating that 3% by weight of oat and rice hulls should not be added, aligns with best practices in brewing. Oat and rice hulls are primarily used in mashing to improve the flow of water through the grain bed and to prevent stuck mashes. However, excessive amounts can have negative effects on the brew process.

Adding too much of these additives can increase the overall percentage of non-fermentables in the beer, which can detract from the beer's flavor and mouthfeel. When these hulls exceed 3% of the total grain bill by weight, it could lead to an imbalance, affecting the yeast's performance and ultimately the quality of the beer. Maintaining a cap at or below this level allows for the benefits of improved lautering while minimizing potential downsides.

Therefore, the recommendation to limit the addition of oat and rice hulls to 3% of the total grain weight helps ensure a successful brewing process without compromising the final product.