iStill Whisky Mashing: Grain to Water Proportions!


The iStill is not just a still, it is a complete distillery in itself. The iStills can mash, ferment, and distill. No more need for mashers, fermenters, and/or stripping runs? How’s that for flexibility and ease of use? Quite the game-changer, yes, we know, but that’s not the topic of today’s iStill Blog post. What is? Well, let’s dive deeper into grain to water proportions. How much grain can one dump into the iStill? We’ll use the iStill 2000 as a reference. If you want to translate that to your i500, just divide by four. Do you run an iStill 5000 instead? Multiply the examples underneath by 2.5.

What is your goal?

Mashing is the first step in making spirits. It’s where you break-up starches into fermentable sugars, so that – in the second step of making spirits – yeast can convert those sugars into alcohol.

The more grain you mash-in, the higher the sugar content of the fermentation will be, and the more yield you’ll get. The less grain you mash-in, the lower the sugar content will be. High sugar content washes are best for lighter spirit profiles. Lower sugar content washes result in lower yield but provide higher relative flavor content in the end-product. Lower sugar washes are best for heavier spirit profiles.

Rule of thumb

Here’s an easy to remember rule of thumb: use four liters of water for every kilo of grain. Or, going imperial, 2 pounds of grain per gallon of water. How this translates to the iStill 2000? Use 1600 liter of water and about 400 kilograms of grain. It will get you to about 8% after fermentation.

Beginner protocol

As a beginning distiller, or a distiller working with new (iStill) equipment, we always advise caution. A good start builds confidence. Overcharging or overfilling your still will create a mess, and takes away confidence.

On a first mash, we advise a grain dump of 375 kilos on 1600 liters of water. Use the agitator to the max, dump the grain slowly, and preferably use a hydrator to make sure the grain is wetted before it enters the kettle. Why the lower than 400 kilo grain dump? Because even with imperfect mixing, conversion, etc. you are still well within the threshold of the still’s filling and heating capacity.

What to expect from a 375 kilo grain dump on 1600 liters of water? An SG of 1.069. With a FG of 1.010, this results in a theoretical yield of 7.61%, when fermentation is done. Taking some losses due to CO2 vent-off released alcohol and yeast propagation at the earliest fermentation stage, expect a net yield of 7.1 to 7.2%. Did everything work out okay? Move up a bit and go towards maybe 400 kilo’s of grain on your next run.

Advanced protocol

As you grow experience and confidence, here’s a protocol that pushes it to the limits. 1600 liters of water and 440 kilos of grain. On this mash protocol, you need to use both the agitator to the max, and bring the iStill Mash Pump into play. How? Recirculate the mash via the drain and iStill Pump back into the boiler, while you mix and add more grain. This makes sure that – even at the higher grain dump levels – all grains are dissolved and wetted perfectly. Essential for maximized yield.

What to expect from a 440 kilo grain dump on 1600 liters of water? An SG of 1.081. With a FG of 1.010, the result is a theoretical yield of 9.158%. Considering that yeast propagation – in the early fermentation stages – and CO2 release result in some losses, expect a net yield of 8.5 to 8.6% for your whisky.

Here’s the complete calculation (thanks Richard!)