Distilling Craft: Ep 004

Gleaming Scales with Lukas Smith

In this episode, we are talking about load cells. Later in the podcast, I bring in Lukas Smith out of Cotton & Reed out of Washington D.C. and we talk about how creating herbal flavors in spirits and cocktails.

Due to the temperature fluctuations that are intrinsic to the distilling measuring volume and using it to make changes can be very difficult. One thing that is consistent though is weight or mass and as long as you aren’t moving your distillery around the world weight is just as good as mass. Since the weight doesn’t change it becomes much easier to be consistent if everything is measured by weight rather than volume so adding pounds of corn to your gallons of water for mashing becomes adding pounds of corn to pounds of water or your pint of yeast nutrient becomes a pound of nutrient. That way you’ll be adding the same amount of everything weather it’s the middle of summer and it is 80 in your distillery or the middle of winter and it’s 60. In order to weigh everything out, you’ll need to have your tanks on load cells and then appropriately size scales for your other operations.

The easiest way to see this work is the example of making rum. If you’re adding molasses to water it will mix up much quicker if everything is about 100°F If you put in 500 gallons of 100°F water it will weigh about 4144 lbs but if you put in 500 gallons of 60°F water then warmed it up to 100°F it would weight 4165 lbs if it was the middle of winter and your cold water was coming out at 40 then it would weight 4173 lbs. If you are adding the same two 50-gallon drums of blackstrap molasses each time your degrees Plato would vary from 12.65 to 12.57 which is basically equivalent to leaving half a gallon of molasses in the drum. This, unfortunately, scales up linearly so a small problem at 500 gallons can turn into a much larger problem as you grow. On a related note, you should be using degrees Plato to measure your fermentations and it is a weight/weight ratio. With yeast, pitch rates need to be consistent as that will affect the flavors that are produced. Rule of thumb guidelines are typically given at ¾ million cells per mL per degree Plato for most distiller’s yeast or about 17.9-17.8 trillion cells or 1.8 Kg (dry) for our ferment above. It would be best to weigh out your yeast prior to pitching but it would also work to just pitch a 2-kg block at you preferred temp as well. The scales are mainly there to make the fermentations more consistent.

Where fermentations get interesting with load cells is in monitoring the fermentation. In our example above we’ve put 1,200 pounds of molasses into out 4,173 pounds of water and assumed that our molasses was 50% fermentable. Since we won’t need any other nutrients our final weight in the fermenter should be (1,200+4,173+4) 5,377 pounds. Since this is a pretty easy fermentation we should convert all of the sugar to ethanol and after all of the CO2 has bubbled off the fermenter should weigh (306+600+4173+4) 5,084 pounds and be 6% ABW. To figure that out we assumed that nothing leaves the fermenter except for the CO2 and used the basic fermentation equation:

2 sucrose = 2 ethanol + 2 CO2

Or 180 pounds of sucrose will create 92 pounds of ethanol and 88 pounds of CO2. If nothing leaves the fermenter except the CO2 then the rest of the weight will still be there and we just have to convert the sucrose weight into ethanol and remove the CO2. This won’t happen linearly but if your fermenter weights 5,250 pounds you can say that you are 43% of the way done with your fermentation. One masking agent to this will be how completely your CO2 vents but after a couple of runs on a recipe you’ll know your finishing weight pretty exactly. The other side of this is for distillery safety where you need to monitor the amount of CO2 that is being vented into your distillery. Going back to our Episode 2 example this 500 gallon fermenter could create a dangerous situation in a 400 sqft fermentation room with 20 ft ceilings after only a third of the fermentation (about 1 day) is complete assuming no ventilation but with 0.6 CFM (assuming a bunch of things, please, don’t use this number for safety) you would be able to ventilate faster than the fermenter could produce CO2 until you expand and run three fermenters simultaneously.

When pumping out your fermenter it’s useful to know how much is being left behind either because you want to minimize the amount of fluid above the trub or you are pulling out of the same fermenter multiple times to fill you still. Since you are monitoring the density of your fermenters, either way, Plato, SG, or Brix, you can use the weight to determine volume exactly without needing to be consistent in the temperature that you drain your fermenter at. Simply take your “final” gravity right before each pump out and then monitor the weight decrease in the fermenter. If you are running a 1,000-gallon fermenter with a 1,500 L still (400 gallons) and are having foaming problem so you don’t want to completely fill your still you could do three equal pulls (say one per 8-hour shift) of 3,389 pounds and know that even as your fermenter cooled over the course of the day you were getting the same amount of wash in each pull.

This system works even better if you also have you still on load cells. If we know that 3,389 pounds of 6% ABW wash was pulled out of your fermenter but manage to leave 6 gallons in your hose you’ll see that 60 pounds didn’t make it into your still (3,328 lbs.). Where this is most important is in calculating your distillation yield. If you’ve captured 603 pounds at 30 proof (24.67% ABW) did you do a good job of stripping? If you’re just assuming everything that comes out of your fermenter is distilled then you’ll find that you yielded (603*.2467)/(3389*.06)=73.2% of your ethanol where in reality you got out (603*.2467)/(3328*.06) =74.5% and while still not a great run you did better than you thought. As with fermentation, we can also track the percent completion of our distillation and also like our fermentation this isn’t linear since the molecules that come off later will be heavier than the earlier ones. That being said if our 1,500-liter still starts out at 3,328 pounds and we capture 603 pounds then we’ve left 2,725 pounds in the still and you can check your still weight and at 3,000 pounds say that you’re 54% of the way done. Also, like the fermenter, you can plot the weight change over time and discover the rate of change and use that to be more exact in your predictions. I find this to be helpful in running the distillery where I can tell a vendor that they can show up for a sales call in 2 ¾ hours knowing that I’ve got 46% of my distillation left.

Just so we can track the numbers all of the way through let’s distill out the rest of our fermenter and capture the same thing each time and then load 1,809 pounds of 60 proof low wines into our 1,000 L still and then capture 770 pounds of 120 proof (52.15% ABW) rum. Now if we’re going to be diluting this rum to bottle our white spirit we need several things. We need to know the proof of our rum, the temperature of our rum the volume captured and the temperature of our dilution water. From there we can use out gauging manuals and calculate the correct volume. Typically, this is an iterative process due to inaccuracies in volume and temperature measurements. On the other hand, if you can stick the rum into a sealed tank then you just need to weigh it, find the proof and then add your 433.7 pounds of water slowly enough to the tank to get the proper weight addition. From here you can fill each 750 mL with 1.57 pounds of rum and fill almost 64 9-L cases.

Where all this tracking becomes useful is that once you know that you are getting the exact same recipe each time and are then able to follow that booze all of the way through the process including where you are losing what you are creating you are then able to come back and understand where it is valuable to focus. The 18 gallons that you lost in the hose cost you 7.1 pounds of booze so that’s about 3 bottles worth that easy to capture but considering that 153 pounds of ethanol were lost stripping it is probably a better place to focus by bumping the percent alcohol that you put into your still.

Outside of the rum world, I’ve been using load cells a lot in dealing with grain delivery systems. With the milling regulations that are coming into play across the country more and more, craft distilleries are opting to have their grain delivered to their mash tun in a slurry form. In order to create these slurries load cells are very helpful in correlating the rpm of the rotary valve to the weight loss on the load cells and then matching that to the influx rate of the strike water, the other way is in ensuring that the total amount of grain mixed is correct. This system can be seen in the drawing below. Similar to the rum example above, 1-ton super sacks from Briess are plus or minus 250 pounds (12% variation) but their ½-ton super sacks are also plus or minus 250 pounds (19% variation) so just dumping a 1,500 pound super sack into a 500 gallon fermenter can adjust your yield by 15.9%. The load cells will help make sure that you’re mixing the right amount of water into your slurry so that it stays pumpable but when you have a high proof or low proof batch you can trace back and figure out why. Load cells will also enable you to verify how much grain is in you silos so that reorders can be made at the appropriate intervals.

Another place where this variation can occur is in you barrel house we’re all required to track how much goes into a barrel and what we get out and typically we’ll average that over say a two-year aging period and say that the losses occur constantly over that time. If you mount load cells either in the form of scales below your stacked pallets or on your racks then you can monitor that loss (averaged over several barrels) over the life time of your aging. To go back to safety if you are losing large amounts of angel’s share in the summer we’ll need to bump your ventilation in the summer to prevent build up to a higher level than we would just by looking at the annual average. That’s not strictly true because we over engineer our systems to account for this so maybe you could save money on a smaller system. Also, parts of the warehouse are having more evaporation than other parts maybe by a warm South facing wall you might want to have the barrels that were then last summer move over to the North side for their second summer to help maintain product consistency.

While I love data and it’s easy for the guy not spending money to recommend putting load cells every where and tout their amazing benefits the question for everyone with a fixed budget is where is the most useful place to put them or where should I start. Everyone should be proofing with a scale if you not it will make you life a million times better over night and decrease the time you spend proofing and iterating to a half or a third of what it is now. The fermenters are very useful from a safety perspective and ensuring that you have a good handle on what your recipe is and ensuring consistency at the start. Due to the safety concern, I’d probably move the fermenters slightly ahead of proofing but either one is a good choice. Tracking your barrel warehouse is probably next but it is a distant third to the first two since you can use it for both safety and to improve the consistency of your product. The still tracking is nice in a data nerd way and I’d recommend at least weighing your low wines and hearts so that yield tracking can be more accurate regardless of their temperature but it’s certainly not required.

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