boil impact on colour

src/mclachlan/brewday/math/Equations.java

@@ -282,6 +282,40 @@ public static ColourUnit calcColourSrmMoreyFormula(
 		return new ColourUnit(1.499D * (Math.pow(mcu, 0.6859D)), Quantity.Unit.SRM, true);
 	}
 
+	/*-------------------------------------------------------------------------*/
+
+	/**
+	 * Calculates the colour impact of a boil.
+	 *
+	 * @param colourIn
+	 * @return
+	 */
+	public static ColourUnit calcColourAfterBoil(ColourUnit colourIn)
+	{
+		//
+		// Brewday has an issue with colour calculations: existing formulae (eg Morey)
+		// require the use of MCUs based on post-boil gravity. But Brewday can't
+		// easily do that because the process steps are decoupled and there isn't
+		// necessarily a 1:1 mapping from mash to boil.
+		//
+		// One option would be passing MCUs around in volumes waiting to arrive at a
+		// post-boil gravity. I doubt this would work properly and haven't tried it
+		// yet.
+		//
+		// Instead I'm doing this: the typical brew process produces a post-boil
+		// volume about 60% of the input water. Working out a table of SRM values
+		// shows me that the SRM output is 42% higher when the MCU's are worked
+		// out with 60% of the water.
+		// So to model this in Brewday at boil time we increase the SRM by 42%.
+		//
+		// This is kinda wacky I admit. But to quote Palmer, there are "inherent
+		// limits of any model for beer colour".
+		//
+
+		double srmIn = colourIn.get(Quantity.Unit.SRM);
+		return new ColourUnit(srmIn*1.42, Quantity.Unit.SRM);
+	}
+
 	/*-------------------------------------------------------------------------*/
 	/**
 	 * @param volumeIn in ml, assumed SRM of 0

src/mclachlan/brewday/process/Boil.java

@@ -146,9 +146,10 @@ public void apply(Volumes volumes,  EquipmentProfile equipmentProfile, ProcessLo
 		PercentageUnit abvOut = Equations.calcAbvWithVolumeChange(
 			inputWort.getVolume(), inputWort.getAbv(), volumeOut);
 
-		// todo: account for kettle caramelisation darkening?
-		ColourUnit colourOut = Equations.calcColourWithVolumeChange(
-			inputWort.getVolume(), inputWort.getColour(), volumeOut);
+		// colour changes
+		ColourUnit colourOut = Equations.calcColourAfterBoil(inputWort.getColour());
+		colourOut = Equations.calcColourWithVolumeChange(
+			inputWort.getVolume(), colourOut, volumeOut);
 
 		BitternessUnit bitternessOut = new BitternessUnit(inputWort.getBitterness());
 		for (IngredientAddition hopCharge : hopCharges)

stufftodo.txt

@@ -1,10 +1,9 @@
 water chemistry & pH
 mash hop, misc additions
 boil misc additions
-first wort hop additions
-boil step: add kettle caramelisation colour change
 persistence back ends: Github, Dropbox
 ---------------------
+first wort hop additions
 right click menu for ingredient additions/step options
 import from beersmith
 packaging 2: javapackager?
@@ -15,6 +14,7 @@ fix yeast pitch rate impact
 batch/inventory integration
 shopping list document generation
 ---------------------
+package step: kegging, krausen and other carbonation methods
 extract & partial mash brewing
 tools on the step pages: eg target mash temp
 UI support for user selected units of measurement
@@ -25,5 +25,5 @@ bitterness: rager, gareth methods
 decoction mashing
 ferment step: multiple yeast additions, yeast blends
 ferment step: impact of yeast addition size
-package step: kegging, krausen and other carbonation methods
+