Stiff starter hydration check (#80)

This adds an explanation and enhanced guidelines on what to look out for
when making a stiff starter.

book/sourdough-starter/sourdough-starter-types.tex

@@ -186,8 +186,24 @@ The stiff starter is the driest of all the starters. It has a hydration of
 around 50 to 60 percent. So for 100 grams of flour you are using around 50 to
 60 grams of water. If you can't mix flour and water because the
 mixture is too dry you need to increase the water quantity. This is often
-the case when using whole wheat flour to make your starter. The stiff
+the case when using whole wheat/rye flour to make your starter. The
-starter should have the consistency of pasta or pizza dough.
+more bran your flour contains, the more water your flour can absorb. The stiff
+starter should have a comparable consistency to pasta or pizza dough. When
+mixing the starter there should be no chunks of flour left. Test placing
+the starter on your kitchen counter. When lifting it should slightly stick
+to your counter's surface. This test indicates that you hydrated the flour sufficiently.
+When the mixture is too dry, the fermentation speed is greatly reduced and
+the starter will seem inactive. The starter should be much drier
+than a regular starter, but also not too dry. Refer to figure \ref{fig:stiff-starter-dry-check}
+for a visual example of the starter's required hydration level. 
+
+\begin{figure}[!htb]
+  \includegraphics[width=\textwidth]{stiff-starter-dry-check.jpg}
+  \caption{An image showing you a stiff starter that is too dry and one that is perfectly hydrated.
+  The starter shouldn't contain chunks of flour and slightly stick to your counter top. The
+  starter in the picture is made with whole wheat flour.}
+  \label{fig:stiff-starter-dry-check}
+\end{figure}
 
 \begin{figure}[!htb]
   \includegraphics{figures/fig-stiff-starter-conversion.pdf}