I've spent the last week or so planning my last two beers of this year. One will be a Berliner Weisse (my first attempt at the style) and the other a New Zealand hopped weizen. One of the features I've been working to add to my Brew Designer application for some time now has been IBU calculation for hop stands and mash hopping. I'm planning to use both of the two methods in these last beers of 2014 (mash hopping in the no-boil Berliner and a hop stand in the weizen), so I thought I'd write a little of what I've learned about these techniques. Hop stands and mash hopping contribute some bitterness to beer, but the lower temperatures involved in both mean that the bittering effect is much lower than during the boil. The reason for using both techniques is to maximise the extraction of aromatic compounds from the hops. These compounds tend to be very volatile and so tend to be lost during a long boil.

Bitterness in beer is primarily the result of iso-alpha acids extracted from hops. Hops contain varying amounts of alpha acids, which are not significantly bitter, but which, when heated, are isomerised to iso-alpha acids, which are intensely bitter. The amount of alpha acid in hops ranges from a low of around 2% by weight in old-world varieties like Saaz, to over 15% in newer, high-alpha varieties such as Magnum or Summit. The rate of isomerisation increases with temperature and rapidly falls below significant levels at temperatures below boiling. I wanted to add logic to the application to allow me to determine the amount of bitterness contributed by mash hopping and hop stands.

In mash hopping hops are, as the name suggests, added to the mash, rather than to the boil. Due to the lower temperatures alpha acids in the hops are isomerised at significantly lower rates than during the boil, resulting in substantially lower bitterness. Interestingly, it appears that the aromatic compounds extracted from the hops during mash hopping survive the boil and into the final beer. Mash hopping is also a way of adding hops to beers such as Berliner Weisse which are not boiled.

For a hops stand, hops are added to the wort after the boil and the wort is allowed to stand without being cooled for anything from 10 minutes to overnight. The wort temperature is typically somewhere between 90°C and 70°C. These lower temperatures mean that many of the volatile aromatic compounds in the hops are retained in the wort and thus in the resulting beer.

Utilisation

Essentially what I wanted to find out was how alpha acid utilisation (the proportion of total alpha acids from the hops to make it into the final beer) varies with temperature. This turns out to be a fairly difficult question to get an exact answer to. There is some research into this (see for example this) but it's not entirely clear to me how to translate the results obtained in such, closed-system studies, to the real world. What most sources seem to agree on is that the utilisation at mash hopping temperatures (~ 60 - 70°C) is somewhere around 20% of what you would get during the boil and at the 70 - 80°C range perhaps 30% of boil utilisation. I use the Tinseth formula in Brew Designer, and so until I come up with more reliable numbers I simply adjust my utilisation figure to either 1⁄5 or 1⁄3 of that for the boil to account for the lower utilisation. This isn't a hugely reliable calculation, but as my IBU calculations are probably pretty imprecise and as most people would probably struggle to distinguish a difference of a few IBU one way or another, it should allow me to make some rough estimate of bitterness generated by these hopping methods.

When I started brewing it didn't take long before I came to the conclusion that pen-and-paper was insufficient for recipe design and record keeping. I'm a developer, so my natural reaction when confronted by a problem is to say "I bet I could do this with a script!" I'd tried doing it all in Excel, considered using an existing software solution like beersmith, but there's no substitute for just coding it yourself. So I wrote an app to handle (almost) all of my recipe design and logging needs.

Every now and then I'll write up a few words about problems and solutions and other trivia that I've encountered writing this app. For now here is a (very) brief introduction to what I have done so far. NOTE: The application is not available publicly just yet, I still have a few features to add and issues to solve before I consider it ready to distribute.

The app is built around three primary views: the recipes list view, which shows a list of all the recipes you've created, the recipe detail view, which allows the viewing and editing of individual recipes, and the brew log view, which details the progress of a specific brew session. There are additional views which allow the management of ingredients, system settings, etc.

The app handles all the necessary calculations for gravity, IBU, colour, and so forth. It allows me to keep detailed logs of how my recipes turn out, record measurements of fermentation progress and even add pictures of the final product so that when I repeat recipes I'm able to easily access all the information I gathered the previous time I brewed.

There are a few things still missing from it though. I don't currently do any water preparation calculations as the whole issue is sufficiently complex to have put me off tackling it so far. I also want to add a yeast pitching rate calculator as well as to figure out some way to deal with split batches. Beyond that there is a list the length of my arm of other, smaller, issues and bugs...

Technical Details

• OS: Windows
• Language: C# .Net 4.5 using WPF
• Data Storage: SQLite
• UI library: mahapps.metro