Sprayheads on batch-brewing machines fall into two categories: those designed for durability, which require very little maintenance, and those designed to evenly distribute water, which require regular maintenance. The designs intended for durability are intended to be limescale resistant. They achieve this by working like a network of open-topped gutters. Usually, these designs separate brew water into fewer than ten individual streams. This style of design is particularly prone to causing wells in the coffee bed, which leads to localised channelling. These sorts of sprayheads are not suitable for specialty coffee applications.
Illustration: A moulded sprayhead with 12 gutters
Systems designed to evenly distribute the water into as many separate streams as possible tend to work better. However, this area of innovation in coffee-brewing equipment is very underdeveloped. The diameter of the holes in each sprayhead often considerably differ from each other. Even 24 separate streams of water spread over a coffee bed with a diameter of around 15 centimetres will create wells in the coffee bed. The higher the number of streams, the more each stream is diffused by the neighbouring stream.
The water sitting above the level of the coffee bed begins to help diffuse the impact of each stream of water from the sprayhead. Insufficiently thick coffee beds that promote a fast drawdown will have less water in the slurry at any given moment because the percolation process will occur at a higher flow rate. Brews with low drawdown-to-time ratios are more susceptible to the formation of wells. If your recipe preference tends towards faster drawdown times, then we advise you to use a sprayhead with as many holes as possible.
Illustration: A perforated steel plate sprayhead
The more separate streams in a sprayhead, the smaller the holes need to be in order to ensure the flow out of each hole is equal. An important consideration is whether the sprayhead has a sufficient diameter and/or spread to distribute the water equally over the surface of the coffee bed.