Wort separation and cooling are two steps in the fermentation process that can significantly impact the quality of the final product.
As the term implies, wort separation is about efficiently and cleanly separating the wort from the solid grains, ensuring maximum sugar retrieval. Wort cooling is all about swiftly bringing the wort’s temperature down to a level conducive for yeast activity. Both are important steps in ensuring a smooth fermentation process.
For new distillers looking to sharpen their techniques, understanding these processes in depth is key to making great whisky.
Here’s a quick run through of the process, what’s involved and what you’ll need (and need to focus on) to do it well.
Wort separation
The aim of wort separation is really simple. To efficiently and cleanly separate the wort from solid grains to retrieve the maximum amount of sugar.
To separate wort, you need a vessel that allows for accurate control over the grain and water amounts which facilitates the separation of wort from grain. This is not much of a bolt on from what you need to carry out a successful mash. In fact, in distilling, wort separation often happens in the same container where mashing occurs like the mash tun, semi-lauter or lauter tun.
It’s worth noting that how it works for brewers is slightly different to whisky. Namely brewers might have specialist equipment and vessels solely used for the job. This is part due to their need for clear wort and the fact that they boil the wort (distillers don’t).
The two items of equipment most frequently encountered are Mash Tuns, which feature a false bottom with perforated plates, or Lauter Tuns which feature rotating rakes and a sprinkler system to mix and rinse the grains. It’s also common to come across a semi-lauter tun (similar to the big version but with fewer functionalities).
Meanwhile a specialist Mash Filter is less common due to the price. Mash filters are highly effective pieces of equipment especially when dealing with fine grain sizes. Most distilleries with a mash filter use a hammer mill for very fine grists.
Types of Whisk(e)y and the impact on wort separation
The type of Whisk(e)y being made also dictates the ideal wort separation technique. For example, distilleries making Bourbon often opt for ‘all-grain-in’ fermentations. For them, almost no separation is required.
On the flip side, distilleries that choose to separate the grain entirely tend to be making whisky from 100% malted barley. Some use the husk from the barley (thus why control grist ratio is important during milling) to act as a natural filter during the wort separation process. Others have specific techniques to help get as clear wort as possible.
Separation techniques
It is easy to assume that separating the wort is a case of opening up the valve on a mash-tun and letting it flow out. After all, as the grain in a mash tun is placed over perforated plates that have a false bottom, there is a lot of the sugary wort is concentrated beneath and a barrier acting like a sieve. Right?
Not so much. If you just drain and do nothing else, it is hugely inefficient. You might not get the solid particles coming out in the wort, but much of the fermentable sugar would remain in the grains. You need to get that out too.
As always with whisky making – doing it efficiently and consistently is the name of the game. There are a few methods distillers use.
Vorlauf technique
The Vorlauf technique is a brewing step where the initial wort that’s taken from the bottom is recirculated back over the grain bed. It then trickles down once more before being collected once more.
The result is highly effective at extracting more sugars and clarifying the wort, preventing grain particles and other solids from entering the boil kettle.
In simple terms, think of Vorlauf as a “pre-filter” stage. The first time you drain the wort from the mashing vessel, the liquid contains tiny solid particles. By recycling this cloudy wort back over the top of the grain bed, the grains themselves act as a natural filter, helping to clean the wort. The result is a clearer, purer wort (that’s also extracted a little more sugar) ready for the boiling stage.
Sparging and if using the Vorlauf, further sparging
Sparging is the process of rinsing the grain bed with hot water to extract any remaining fermentable sugars after the initial wort has been drained from the mashing vessel. The aim is to maximise the efficiency of sugar extraction.
Sparging ensures that as much sugar as possible goes into the wort for fermentation.
In simple terms, think of the grain bed as a sugary sponge. After the first wort is drawn off, some sugars are still left in the grains. Sparging rinses these leftover sugars into the wort, which then goes on to be fermented. This makes the mashing process more efficient and cost-effective, as it extracts more fermentable material from the same amount of grain.
If you do it several times, it’s known as batch sparging. It’s also where the term Second Waters and Third Waters come from (literally second or third rinse). Sparging several times is based on the same idea as above – to get the most out of your grains.
Wort cooling
Once it’s been separated from the solids (or most of them) – it’s time to cool the wort.
The main objective is to reduce the wort’s temperature from its mashing temperature to a range suitable for yeast fermentation, ideally between 20-30˚C.
Typically, it’s carried out through a Plate Heat Exchanger, which consists of several metal plates where hot wort and cold-water pass in a counterflow manner. This design ensures the two liquids don’t mix, and heat is transferred efficiently from the wort to the cold water.
Not only does this cool the wort, but it can warm the water (thus the “exchange”). If collected, that warm water can be used in the next batch, having already been brought up in temperature considerably. This requires less energy (read cash and carbon) to get to temp. The design works most effectively when using grain-free wort.
Another method is by using a Shell and Tube Exchanger. These are mostly found mainly in larger grain distilleries where the cooling demand is higher. Here, wort flows inside tubes, and the cooling agent surrounds these tubes. This design is suitable for ‘all-grain-in’ systems since it doesn’t get blocked by solids.
The end result is wort, now cooled, that can be directed to the fermenter and mixed with yeast.
Key areas to focus on in the wort separation and cooling process
If you are a new distillery start-up – to succeed in wort separation and cooling, focus on investing in quality equipment, continuously training the team, and implementing a robust quality control system. Split your planning in two.
Efficient separation
- Understand the differences that the typical types of equipment bring to the process. What are you mashing with and what does that mean for your wort separation options. The most important elements are the different sparging techniques that need to be used to maximise extraction and separation.
- Appreciate why most new distilleries prioritise purchasing reliable and efficient equipment that factor in both wort separation and cooling processes. It ensures consistent quality and reduces long-term operational issues. There’e no point just looking at how the equipment works for the mashing stage. What happens down stream needs to be considered at the same time.
Effective cooling
- Understand the advantages and limitations of different cooling systems. While it is important to rapidly reduce the wort’s temperature to a range suitable for yeast fermentation, there’s an opportunity to make a cost and energy savings with well-designed heat exchange flows.
- Appreciate why distillers regularly monitor the efficiency of sugar extraction and the clarity of the wort. Look at how they go about implementing systems that provide real-time feedback on these processes. How will you do this too?
Wort separation and cooling is just one of the many parts of making whisky. If you are looking to get informed about other aspects, why not look at our articles on Storage & Milling, Mashing, Yeast and Whisky Specific Fermentation to continue your reading.
