Ask Mr. Wizard

Beer Spicing Decisions


Sonny Lachance — Drumondville, Québec asks,

I am planning to brew Dixie Cup Boardwalk Belgian Quadrupel from the byo website. I am wondering if I add spices and raisins at the end of the boil will there be enough time for the aroma compounds to dissolve into the wort before cooling with a plate chiller?


A Flavor extraction is almost always influenced by particle size. Indeed, the only times this is not true is when the compounds of interest are not soluble in the solvent being used for the extraction. In brewing, there are really two solvents of practical interest. Water is the solvent at play during the production of wort, and beer, or water + ethanol, is the solvent when ingredients are added to beer. Crushing or milling spices is the best way to improve extraction efficiency of your spice additions and chopping or blending raisins will give more tang for the buck than whole raisins. And adding your spices and raisins towards the end of the boil should provide more aroma retention than adding with several minutes left of boiling. That answers the question and I don’t have anything else to say about that.

But there are two related things that are noteworthy. The first is about your wort cooler. Plate chillers, usually called PHEs or plate heat exchangers in commercial circles, are the most efficient heat exchanger type used for wort cooling for several reasons. The most significant aspect of the design of these devices is the surface contours of the plates. Although different plate patterns are used for various applications, PHE plates all resemble an old-fashioned washboard. The plates in a PHE are stacked up and flow paths through the plate pack are established by holes in the plates that direct coolant and product through the unit. Because the plates are closely packed, the liquid film is thin, and because of the shape of the plates, the flow is highly turbulent. These attributes, coupled with the minimal thickness of the plates, increase the overall heat-transfer coefficient, or U-Value, and make these heat exchangers very efficient compared to other designs, such as tube-in-tube and immersion chillers. Add a high surface-to-volume ratio to the relatively high U-Value, and the result is pretty amazing.

The design features that make PHEs highly efficient heat exchangers can also be a weakness. Bits and pieces of hops, malt husk, citrus peel, fruit skins, coffee grounds, macerated raisins, and coriander seed can all become trapped inside of a PHE. In extreme cases, these solids will clog the PHE and the problem is obvious. Yet other times, particles will reside in a PHE to simply become breeding sites for microbiological growth without having an obvious effect on wort flow. The take-home message is to keep particles out of your wort cooler.

The other point your question raises is about crushing or milling of spices and other ingredients like raisins. Decreasing the particle size of these ingredients will absolutely speed extraction, but it also changes the recipe. If you have been adding two cinnamon sticks at flame-out, for example, to brew a beer that you love, be careful before you decide to start milling the cinnamon because you will most certainly end up with more flavor from the cinnamon. You also need to be mindful that powdered spices are mainly composed of insoluble bits of bark, plant leaves, and seeds; these fine particulates tend to settle around low velocity areas in a heat exchanger and can begin to fill the PHE with particles similar to silt around a river delta. And that’s all I have to add about that point. Here’s to fun additions to wort and efficient wort cooling!

Response by Ashton Lewis.