Continuous Fermentation!


Whiskey production consists of mashing, fermenting and distilling. Rum and brandy production do not need mashing, but still need fermentation and distillation capacity. Making your own alcohol is a multi-step process and in multi-step processes, there is always a bottle-neck. Guess what the bottle neck is for rum, brandy, and whiskey production? Yes, fermentation.

Where mashing can be done in like 4 hours, and distillation takes a about 8 hours, it is the fermentation part of spirits production that is the slowest. Depending on product and procedure, fermentation can take 3 to 4 days.

The traditional approach in the distilling industry, in order to overcome the fermentation bottle-neck, is to add more fermenters. For instance, 5 or 6 fermenters for each masher or still.

Even though this is the standard way to deal with the fermentation bottle-neck, there are severe draw-backs to this solution. To name a few:

  • Expensive: six new fermenters … that’s a lot of money;
  • Floor space: six new fermenters … that takes a chunk out of your distillery space;
  • Workforce: pumping, cleaning, managing multiple fermenters is more work;
  • Versatility: if you grow, do you buy more fermenters or bigger ones?

Since iStill likes to challenge traditional approaches, here is another take on fermentation. I hope it broadens your horizon and helps you design your perfect distillery with more ease.


Let’s call the solution I propose “Continuous Fermentation”. The thinking is as follows: “If fermentation is the bottle-neck in alcohol production, that’s the one step we want to do continuously”. The question now becomes: “Can we do so while limiting the number of fermenters, thus limiting capital investment, occupation of floor space, the number of staff needed, while simultaneously boosting flexibility?”

That’s a long question, but luckily the answer is short. One. You just need one fermenter. How’s that for disrupting things, right? And more importantly: how would that work?

If fermentation is the bottle-neck and multiple fermenters isn’t the solution, how do we solve the puzzle? Well, if we limit ourselves to just one fermenter, we make it bigger. Imagine that you have an iStill 500 to distill your whiskey, rum, or brandy in. As a fermenter you’d need one 2000 liter version. One 2000 liter version instead of 5 or 6 smaller ones. Do you run an iStill 2000? In that case consider purchasing an iStill Fermenter 5000.

Now, I hear you thinking: “So I have to wait for 3 or 4 days to ferment 5000 liters … and then I need to do 3 runs in my iStill 2000 to process that? Where’s the gain?” Stay with me, and read my proposed change in procedure:

  1. Ferment 5000 liter;
  2. Take up to 2000 liter out of your f5000 and put it in your i2000 for distillation;
  3. Fill-up the fermenter with fresh substrate and water to 5000 liter;
  4. Do the distillation run in the iStill 2000;
  5. Next day? Take up to 2000 liter out of your f5000 and put in in your i2000;
  6. Fill-up the fermenter with fresh substrate and water to 5000 liter;
  7. Do the distillation run in the iStill 2000;
  8. Etcetera.

If a full fermentation takes 3 days, what happens, if we take out (around) 1/3rd for distillation, and we fill-up the fermenter again with new substrate and water? Well, the substrate and water will mix with the (already fermented) beer or wine in the f5000. The introduction of new fermentable sugars will kick-off fermentation again, but since you only add 1/3rd of the “normal” amount of sugars in, fermentation will now only take one day!

By adding just one oversized iStill Fermenter to your distillery, you can start continuous fermentation. In the above examples this continuous fermentation cycle helps you perform one iStill 2000 distillation per day. Five days a week, six days per week, or seven days per week. However often you want to.

Need more capacity? An iStill 2000 can do two runs per 24 hours, so maybe add a fermenter? Two f5000’s allow you to basically distill twice a day. No need for 6 fermenters, and certainly no need for 12.

Implementing continuous fermentation for rum and brandy

The substrates for rum and brandy are liquid instead of particle based, like grains, and do not need mashing. If you want to move towards continuous fermentation, just draw-off 1500 to 2000 liters every day, and add more molasses or fruit juice with water to top-up your f5000.

Since yeast is already present, there is no need to add more. Just make sure you mix in the new substrates and water. That’s all. You need a big iStill Fermenter and a (smaller) iStill distillery.

Fermenter 5000 and iStill 2000 for continuous fermentation and distillation …


Implementing continuous fermentation for whiskey

Continuous fermentation for whiskey introduces two minor challenges:

  1. Grains need mashing in order to convert starches into fermentable sugars;
  2. Grains are particles and not fluids like molasses or fruit juice.

So in order to to make whiskey on a continuous fermentation basis, you either need to buy an iStill Masher. In the above example the iStill Masher 2000 will do, because that is the amount you need to add every day.

Or you can use the iStill 2000 for mashing. If you use the i2000 for instance for one distillation run per day, you could use it for overnight mashing.

What you don’t want is to leave the spent grain parts in the fermenter. So you either strain the mash and ferment off the grain, or you mix the fermenter before discharging 2000 liters to your iStill 2000, so that as many spent grains are taken out as you add with each new fill-up.

The optional two additional drains allow for very easy filling …


Innovation: Mashing made easy!


Today, let’s go back to what’s basically the first step in the alcohol production process: mashing. Spoiler alert: we are not just going to talk about mashing, but also about the iStill Masher! You know what? Let’s start with a picture of that amazing machine …


What is mashing?

Mashing is where we turn grain starch into fermentable sugars. We do so by heating-up water, adding the grains, and then adding enzymes (or malted barley) to help the starch to sugar conversion.

Steps and rests

Various steps can be distinguished, where various enzymes do their work. Most importantly:

  • Beta Amylase rest at 62c;
  • Alpha Amylase rest at 72c.

Depending on the grain bill and enzymes each rest can take 30 to 90 minutes. Sometimes additional steps are needed. Corn, for instance, needs much higher temperatures to give up its starch. This makes a boil or high temperature rest at 90c necessary.

When the enzymes have converted the starch into sugar, mashing is done. Before the next step in the alcohol production step can start – fermenting – the mash needs to be cooled down to 25-28c. A cool down is therefore always the last step of any mash process.

Two basic procedures

There are two basic mash procedures:

  1. Step-up mashing;
  2. Step-down mashing.

In a step-up procedure, water and grain is mixed and heated-up and taken through the various mash steps. Enzymes or malted barley (a grain with excess enzymes for starch to sugar conversion) are added along the way.

Basically, in a step-down mash, water is brought to the highest needed temperature (given the specific grain bill), grains and enzymes or malted barley are added, cooling the mash down and taking the process through its various steps and rests.

Step-up mashing is mostly used in the beer industry. Given that step-down mashing is easier, faster, and takes less energy, for the distilling industry most choose a step-down procedure.

What’s important in a masher or mash tun?

Given the above, what masher or mash tun do you need to buy? What’s important to consider? Let’s dive in deeper.

Mashing is a process. What process steps should your mash tun support? Well, mashing takes place at high temperatures, so heating efficiency is important.  And since different enzymes achieve conversion at different temperatures, so is control. Finally, because fermenting – the next step in the alcohol production process – takes place at much lower temperatures than mashing, cooling efficiency is important.

Functionally, it is the craft distiller that does the mashing. So how should the masher support you in your daily operation? Ease of operation for sure is important. The less time you spend mashing, the more time you can spend doing other stuff. And since no whiskey can be made without mashing, longevity is crucial too. Your mash tun needs to be build to last, so it will never become the weakest link in the production proces.

The iStill Masher

With the goal of making mashing easier, iStill introduces next generation mashers. In 5,000 and 2,000 liter net capacity. Here is a picture of the 5,000 liter model:


And here’s what makes them unique:

  1. Efficiency;
  2. Control;
  3. Ease of operation;
  4. Longevity.


Due to its compact design, unique indirect heaters, and insulation, the all new iStill Masher is the most efficient mash tun in the world. A 5,000 liter Bourbon mash costs 360 kWh. At 0.15 Euro or Dollar per kWh, the total costs of mashing are only EUR 54,- or USD 54,-. A single malt whisky mash uses only 240 kWh, which adds up to 36 Euro’s or Dollars.

A Bourbon mash in the iStill Masher 2000 costs 140 kWh, which translates to 21 Euro’s or Dollars. A single malt mash, which takes place at lower temperatures, uses 100 kWh and costs only 14 Euro’s or Dollars.

Both iStill Mashers come with the patented Jet Propulsion Agitator System (J-PAS). Together with the flush square boiler design, it helps limit shearing, which leads to better mixing efficiency, better particle distribution, and optimal heat distribution in your mash. The system counteracts vortex formation too, resulting in both higher fill grades and easier cleaning.


With only 0.1 degree temperature tolerance, the new iStill mashers offer total and unmatched control over the starch to sugar conversion process. Here’s a mash tun that puts you in charge!

Up to 40 individual mash programs can be dialed in. Each program gives the craft distiller control over the number of mash steps (up to 9), the temperatures and power settings during those steps, how fast the agitator should mix, and how long the conversion rests should take.

Ease of operation

The iStill Mashers come fully automated. After you dial in your mash procedure, you just press “Start” and the machine does the mashing for you.

The iStill mashers are connected to the internet. This way you can remotely supervise and control your masher. It also allows us to upload new software or perform remote checks.

The iMasher has auto-start. This enables you to pre-heat your mash water and shave off a few hours of your workday.

Our masher comes with automated programs for Bourbon and single malt whisky mashing. You simply select the program and use our experience to help you mash.

The iStill Masher comes with two big manholes. One at the top (for grain filling) and one near the bottom (for easy access). The PLC is operated via a touch screen or via your smartphone or computer.

Another unique feature the new iStill Masher has, is the Easy Discharge Center. The unit sits, as it were, on stalks. This creates a high and easy access discharge exit. You can easily forklift a receiver/container under the actual boiler for easy cleaning and grain handling. Lastly, it has Easy Filling Connect. Just connect a hose to the connect and you can start filling your masher.


Most mashers out there are made out of 1 or 2 mm thick steel. Since we feel mashing is an essential step to your production process, we decided to beef-up design specifications.

Our mashers use 4 to 5 mm thick stainless steel. They are build to last! The sides are insulated and the insulation is armored for heavy duty use.

The actual boiler is suspended in a strong, stainless steel skid. The skid acts as an exoskeleton that protects your mash tun, and that allows for side-by-side operation of multiple mashers and/or fermenters.


iStill Masher 5000:

  • 5,000 liter net capacity;
  • Insulated flush square boiler design;
  • Weight: 1,000 kilo;
  • Sizes: 170x170x360 (wide, deep, high, in centimeters)
  • Power: 90 kW;
  • Heat-up time Bourbon mash: < 3 hours;
  • Heat-up time Single Malt Whisky mash: <2 hours;
  • Total mash time Bourbon: < 3 hours;
  • Total mash time Single Malt Whisky: <2 hours;
  • iStill Boiler Radiator for direct (instead of indirect) cooling;
  • Manholes: 40/60 cm diameter, one at top, one near bottom;
  • Supports grain as well as potato mashing;
  • Can be used as a cooker as well as a masher;
  • Patented indirect heater system;
  • PLC system and touch screen computer;
  • Automated mashing programs;
  • Internet connectivity, smartphone & computer management and control;
  • Easy Fill Connect and Easy Discharge Center;
  • J-PAS variable speed mixing technology;
  • Optional: WiFi.

iStill Masher 2000:

  • 2,000 liter net capacity;
  • Insulated flush square boiler design;
  • 650 kilo;
  • Sizes: 130x130x270 (wide, deep, high, in centimeters);
  • Power: 36 kW;
  • Heat-up time Bourbon mash: < 3 hours;
  • Heat-up time Single Malt Whisky mash: <2 hours;
  • Total mash time Bourbon: < 3 hours;
  • Total mash time Single Malt Whisky: <2 hours;
  • iStill Boiler Radiator for direct (instead of indirect) cooling;
  • Manholes: 30/50 cm diameter, one at top, one hear bottom;
  • Supports grain as well as potato mashing;
  • Can be used as a cooker as well as a masher;
  • Patented indirect heater system;
  • PLC system and touch screen computer;
  • Automated mashing programs;
  • Internet connectivity, smartphone & computer management and control;
  • Easy Fill Connect and Easy Discharge Center;
  • J-PAS variable speed mixing technology:
  • Optional: WiFi.


The iStill Masher 5000 costs EUR 50,000. The iStill Masher 2000 costs EUR 35.000. Both units come fully pre-assembled. Immediately after being connected to water (in/out) and electricity, it is ready to run your first mash.


The iStill Masher comes in the sizes 2,000 and 5,000 liters. We could probably build it smaller, but why would you want that? Pricing will only go down marginally, and in order to make a living out of producing your own alcohol … well … there is no substitute for cubic inches.

This is the first of a new line of innovations. The iStill Masher performs the first step of your alcohol production process. Expect us to release new products, like an iStill certified pump for easy mash transfer for example, in the very near future! Again, to make mashing easier, to make your  life as a craft distiller easier. This is the first of a wide range of new innovations. Stay tuned! Follow the iStill Blog and follow us on Facebook.

Delivery and availability

Orders or requests for information can be placed via Current lead time is 3 months.

We are building the revolutionary iStill Mashers right now. Wanna buy … ?

Copper is medicine for a bad ferment!

Whiskey making: the procedure

If we exclude grain handling and aging, traditionally, whiskey is made in three steps:

  1. Mashing (converting starches into fermentable sugars by using enzymes);
  2. Fermenting (converting the fermentable sugars into alcohol with yeast);
  3. Distilling (concentrating the alcohol and harvesting the right flavors).

In order to create the best possible whiskey, both in terms of yield and taste, all steps need to be optimized. The end product is the sum of how the various parts are performed.

If mashing is sub-optimal, the major loss you face, as a craft distiller, is yield. You will create less alcohol. A failing fermentation will, above all, have impact on flavor creation. That’s because over 80% (as a rule of thumb) of taste molecules are made during fermentation. Bad distilling procedures can affect both yield and flavor composition of your new make spirit.

Whiskey making: historically

Historically, whiskey was made in small batches. Small mashes are easy to handle. Small ferments do not generate a lot of heat. Small, copper stills were the norm, because copper was available, affordable, and bendable.

In the 1870’s the industrial revolution found its way into the distilling industry. A lot of the whiskey production became bigger and more centralized. A declining number of remaining distilleries that, each on their own, saw a steep increase in production output.

Small batch traditionally allows for good control and therefore good whiskey …

Schermafbeelding 2019-10-02 om 08.59.24

Batch size growth associated problems

As distilleries grew bigger, mashing basically scaled up from small batch to big batch, and yield didn’t suffer. Fermentation scaled up from small batch to big batch as well, and this did created a major problem.

Fermentation creates heat, and the bigger ferments created more heat. The warmer fermentations stressed out the yeast and produced multiple unwanted flavor compounds in the base beer, of which sulfur was (and is) the most important.

In short? As distilleries got bigger, mashing didn’t get compromised, but fermentation did. Yield didn’t suffer, but flavors did. Interestingly enough, it took a few more decades for distillers to realize they actually had a problem.

Bigger, uncontrolled ferments generate bad flavors that copper catalyses …

Schermafbeelding 2019-10-02 om 09.00.19

Houston, we have a problem!

In the 1960’s new metallurgic innovations found their way into the distilling industry. As growing distilleries needed bigger stills, traditional copper stills were replaced with more modern stainless steel set-ups. And guess what? All of a sudden the whiskey they produced had bad, sulfur associated flavors in them!

What had happened, was the following: copper reacts with sulfer. The traditional copper stills had managed to polish-up the bigger, overheated, sulfur-rich whiskey beer! Copper, it turned out, was a really good medicine for a bad ferment.

With SS stills, sulfurs no longer got catalyzed, and bad ferments got exposed …

Schermafbeelding 2019-10-02 om 09.00.29

The traditional solution

The switch from copper to stainless steel stills brought to light a major problem: bigger ferments created off-flavors. The solution the industry rallied toward, was to switch back to copper stills. The copper catalyzed the sulfuric compounds to below the taste threshold, and the problem was solved. Or wasn’t it?

Bigger ferments, left unchallenged, grow too hot, stressing the yeast into making multiple unwanted flavor. Sulfur is the most significant of those and copper does a good job at cleaning up these sulfuric flavors, and at hiding the poorly managed ferments.

So the distilling industry switched back to copper stills …

Schermafbeelding 2019-10-02 om 09.00.38

Compromised solution

Using copper stills, to counter bad ferments, is a treatment of effects, not a root cause solution. By allowing for non-optimized whiskey production via copper stills, the following set of new problems occurs:

  1. Uncontrolled, overheating fermentations create more bad flavors than just sulfur;
  2. The copper clean-up during distillation does not polish-up all of those;
  3. Copper stills oxidize, creating copper contaminated whiskey;
  4. Copper stills need extensive cleaning, making for longer working days;
  5. Due to oxidation and cleaning, copper stills need to be replaced in 10 to 15 years.

Even though copper stills are a medicine for bad ferments, they are not the ultimate solution. Bad ferments create bad flavors, and copper does not counter all of them. More so, copper is a heavy metal that is toxic to humans. Due to the reactive qualities of copper, the distillation equipment needs extensive cleaning. This cleaning, as well as the general levels of oxidation, severely hamper a copper still’s longevity.

The iStill solution

That’s why we started proposing a different approach. Here it is. Let’s call it the iStill solution:

  1. Mash in a controlled environment, to achieve maximum yield;
  2. Ferment in a controlled way, to achieve maximum flavor;
  3. Distill in a controlled way, to achieve maximum yield and flavor.

Our iStills are designed to mash with 0.1 degree temperature tolerance. This gives the distiller the opportunity to maximize yield, which helps optimize production quantities.

During fermentation, our technology brings temperature, pH, and SG under control. This ensures that the distiller maximizes the desired flavor development.

Finally, the iStills have perfect control over the distillation process. This helps the distiller in optimizing both flavor profiles and yield in the most efficient and repeatable way.

iStill gives you the control to make better whiskies …

Schermafbeelding 2019-10-02 om 09.00.46

Design choices

Because we optimize fermentation, the creation of undesired, bad flavors is minimized. As a result, we do not have to build our stills out of copper. This way, we can deliver a still that is easy to clean, does not cause copper particle contamination in your spirits, and has tremendous longevity.

But if you decide you are going to do your fermentation quick & dirty anyhow, well, please know we have copper waffles that you can insert at the bottom of the column. It takes less than a minute to put them in place. It takes less than 10 seconds to take them out, when the run is done. They have the same surface area as a complete copper column, without the hassle.

iStill copper waffles: well-used …






Craft Distilling Training in the Netherlands!

We just started another 4-day iStill University Distillers Training here at iStill HQ in the Netherlands. With 15 participants from Denmark, Norway, the UK, Spain, India, Ukraine, Far Oer Islands, and Japan. Our Japanese students brought presents!


Would you like to be trained at the industry’s best educational facilities? Please know we still have a few places available at our USA and Australian classes. For more information, please check out:

Building Big iStill Distilleries (3)!

Yesterday, we have put two more 5000 liter iStill Fermenters on transport to our Rotterdam Harbor based crater. And guess what we’ll be doing tomorrow? Two more f5000’s will leave us to be shipped to distilleries all over the world.

Do you want to see how you can set-up your own iStill Distillery? Please click on this link:

Do you want to learn more about the amazingly innovative new line of fermenters we developed? Please click here:

iStill Fermenters 5000 being loaded on trucks …

Muscovado and Molasses Rum (4)!

Rum production is ramping up! First, we played around with the Muscovado Rum. We have samples at 45, 48, and 51% and are currently also testing various back sugar levels.

Proofing and back sugaring the Muscovado Rum …


And since the molasses fermentation is doing well, we decided to scale up from the 200 liter test batch size to a full-scale fermentation and distillation on the iStill 2000.

Here is a picture of the iStill 2000 being filled with water and molasses …


We are currently thoroughly mixing the water and molasses. To make sure everything is mixed perfectly fine. A total of around 1950 liters, to which we will add around 1500 grams of yeast. We’ll start fermenting at 22c and will let the temperature go up to 32c before the cooling kicks in. Molasse is a tropical product, and fermenting at higher temperatures helps create a great flavor profile.

When the fermentation is done, we’ll use the iStills unique distillation technology to turn the molasse wine into rum in one go. A single distillation will take the hearts cut to any pre-defined ABV. We’ll probably shoot for 60 – 65%. The advantage of the iStill fermentation and distillation technology in the rum making process?

  1. Perfect control over fermentation pH, temperature, and SG allows for perfect control over flavor composition;
  2. Perfect control over the distillation process allows for a fuller bodied style rum (at 60-65%) or a purer, lighter version (at 90-95%) in one go. The flavor intensity you want, while saving time and energy, instead of wasting it on an additional stripping run.

Automated mixing and heating-up prior to starting fermentation …


Shipping Huge iStill Distilleries!

We are seeing more and more orders. Not just for individual (multi-role) stills, but for complete distillery set-ups as well. Here are pictures of an order (pre-packaging) of an iStill 5000 and an iFermenter 5000. That’s 5000 liter of total mashing capacity, 10.000 liter of fermentation capacity, and 5000 liter of distilling capacity. On a weekly basis, applied to whiskey production, this set-up can produce 6 1/2 barrels (55 gallon each) of 120 proof New Make per week …

Wanna design your own distillery? Here you go:

Building More iStills Nano!

We are currently building a batch of 36 iStills Nano. The iStill Nano is the one liter gin school still that you can order in batches of six. Interested in setting up a gin school to intensify your distillery’s customer experience, please read this thread:

And here is a picture of us building them little boilers …