AUTHOR: ALAN BISHOP
With the rise of the small craft distillery movement in the United States and the drive to find a competitive edge and differentiate products, many distillers have decided to look back at the history of whiskey production in order to determine their path into the future. Everything methodology wise is back on the table again regarding distillation philosophy, just as it should be, just as it was before a handful of industrial producers decided on the single “best” (read efficient) methodology to use across the industry. We recently took a look at the differences between a few types of distilling apparatus as the conversation about Pot Still Vs. Column had become such a hot button topic. In this article we will tackle, in much the same way, the debate about whether sour mash or sweet mash whiskey is decidedly “better” or simply a marketing slant. Just as in the pot vs. column debate, we will present evidence that even those within the marketing departments of companies making the product usually have a poor understanding of the method themselves, if they have any real understanding at all.
Before I go into the history of the two fermentation methodologies, I feel I should give a little basic explanation of what defines a modern “Sweet Mash” and “Sour Mash” fermentation. Here we are simply looking at the most basic understanding used in marketing to differentiate products, later we will break the two categories and their associated sciences and misconceptions down further.
Sour Mashing in the modern sense of the term, is used to define a process wherein a proportion of mash/beer/wine that has already been distilled and had ethanol stripped from it is added in a proportion from 10-35% into the next run of fresh, unfermented mash. The standard marketing tale told on all commercial tours is that this is done to correct the pH downward in order to create a hospitable environment for yeast and to buffer against bacterial contamination. The truth in modern times is a little different yet and as you will see the term prior to the industrialization of whiskey distilling is even more convoluted.
A “Sweet Mash” on the other hand is simply mash with no “backset” (the term which defines the spent mash or slop added to the beer in the sour mash method) or other pH adjustments made (via citric acid, malic acid, or malolactic bacteria). Sweet Mash begins fermentation as nothing more than the yeast working away at a fresh batch of beer or wine to be distilled. As you will see, nothing is ever as simple as this definition makes it appear to be.
Here I will explore the history and wide spread use of both methods and explain some of the theory behind the methods as we go.
In order to better understand the pros and the cons of each of the two methods we should probably take a deeper dive into the history of the two. Much has been written over the years of who the creator of the sour mash methodology was, and unfortunately every scrap of material written about the method has been written from the perspective of the Bourbon aficionado, putting only one category of distilled product to the forefront as ground zero of this valuable technique and ignoring most everything that existed before bourbon was recognized as a category. As well, the people who tend to write distilling articles tend not to be distillers themselves so have only and outsider’s perspective of the processes and the history.
There is no doubt of course that the man who single handedly brought the method to prominence and who “modernized” and standardized the practice was a distiller working for Oscar Pepper at what is now known as Woodford Reserve in the 1830’s. Scottish Dr. James Crow of “Old Crow” Bourbon fame, who used the sour mash method alongside a number of more “modern” tools to take Bourbon distilling from folk art to an industrial science and who subsequently built a legendary and bespoke career for himself. I have nothing but respect for the man (and nothing but disdain for the company who owns the brand but refuses to see its true historic value) and certainly value his contributions to the distilling world, even if he was not truly the originator of the Sour Mash methodology. Of Dr. Crow more than enough has been written so I won’t wax poetic of him here. Instead, I will post his “recipe” for Sour Mash taken from the law library of Mr. T. Noble Lindsey and given by William Mitchel (who worked for Crow) to Van Johnson:
Use in 100 bushels of bourbon mash, 12 to 15% of barley malt, ground, 8 to 10% rye, ground, and 75 to 80% corn, ground. In starting up the distillery and using small tubs, put say 80 lbs. of corn meal in the tub and cook with say 30 to 40 gallons of boiling water.
Let set for 4 to 5 hours, then stir and cool to 150 degrees to 160 degrees Fahrenheit and then add rye, say 8 to 10 lbs. Then cool down by stirring to 135-148 and then add malt, say 12 to 15 lbs. Then cool down to 115 degrees Fahrenheit and add cold water enough to bring it down to 68-78 according to the temperature of the weather.
Then fill the fermenter with water at same setting temperature, then add yeast which has been made say 1 1/2 to 3 1/2 lbs. to the bushel.
Continue the above for four days and thereafter cook the corn meal with boiling slop, then let stand from 12 to 24 hours, then break up and cool by stirring to 122-160. Then add rye, same percent as above, and cool to 120-130. Then add malt and hold for two hours. Then break up, run to fermenters and fill according to the weather, and add either fresh yeast, or yeast taken from the previous tubs.
The tubs for the first three days of the week are set at say 72-78 and the last three days say 66-72.
Then run the beer into the stills, copper preferred and boil until the spirit is practically exhausted. Then run this spirit obtained from first distillation, and which is held in tubs for the purpose, into the copper doubler and their boil until the whiskey so made would show above proof in the receiving room. The remainder being boiled until the whiskey is practically exhausted and which after cutting off is run into the low wine tub and distilled over again.
YEAST. Use proper proportions of rye, say 1 1/2 lbs. to the bushel, and cook same in 15 to 20 gallons of water to a temperature of say 160 to 175 for say 10 to 20 minutes; then follow with barley malt, same percent, and let stand 24 hours at least to sour and cool to 70-76 degrees. Then stock it with jug yeast previously prepared.
Here Dr. Crow is outlining a process for a typical production week or distillery to start up the sour mash process, starting by making what is clearly a sweet mash to start his production and then utilizing his spent mash (still boiling hot from the still) for cooking in the rest of the mash by the end of the week to create his sour mash process. As you can see, if this is what he practiced in his time, then not all the whiskey he made was indeed sour mash in the traditional sense. He may have also have simply been laying out a process for a week of production and if so, I would presume he was blending these sweet and sour mashed whiskeys together in the barrel, but it’s hard to say. What I can’t say either is why he wouldn’t have continuously used the process by making a batch of sweet mash initially and then subsequently always using a proportion of spent mash. I suppose it could be due to a day off in the production schedule since he is specifically using this spent mash to cook in fresh grains and cold spent mash would have held no interest for him. To put it simply it may have been a matter of industrial efficiency for him to use the spent mash in order to cook the new mash. He obviously notated the difference in pH between the spent material and a new unfermented mash as well and saw the same as beneficial to his process, but it’s truly had to tell how deep his “involvement” and “understanding” of all the facets of the process were without any first-hand notes or descriptors. This is important because there is so much more happening with sour mashing than just heat reclamation and pH adjustment, all of which we will come back to shortly after examining other earlier accounts of sour mashing.
Aside from the standard Doc. Crow legend, many writers in the Bourbon sphere have made much of the 1818 Catherine Spears Frye Carpenter recipes for “sweet” and “sour mash” whiskies respectively as a possible origin point for the sour mash method. These were originally brought to light by Historian Michael Veach and latter touted by writer Fred Minnick in his “Whiskey Women” book and associated engagements as “the first recorded sour mash recipe”. A notion, which while interesting, and true for the recipe in Kentucky, is not historically accurate. Catherine Spears Frye Carpenter, who lived from 1760-1848, inherited a Kentucky distillery from her late husband and recorded the methodology for both sweet and sour mash in the following:
“Receipt for Distilling Corn Meal Sweet Mash, 1818
To a hundred gallon tub put in a Bushel and a half of hot water then a half bushel of meal Stir it well then one bushel of water & then a half Bushel of meal & so on until(sic) you have mashed one bushel and a half of corn meal – Stir it all effectively then sprinkle a double handful of meal over the mash let it stand two hours then pour over the mash 2 gallons of warm water put in a half a gallon of malt stir that well into the mash then stir in a half Bushel of Rye or wheat meal. Stir it well for 15 minutes put in another half-gallon of malt. Stir it well and very frequently until (sic) you can bear your hand in the mash up to your wrist then put in three Bushels of cold slop or one gallon of good yeast then fill up with cold water. If you use yeast put in the cold water first and then the yeast. If you have neither yeast nor Slop put in three peck of Beer from the Bottom of a tub.”
“Receipt for Distilling by a Sour Mash
Put into the mash tub Six busheles (sic) of very hot slop then put in one Bushel of corn meal ground pretty course (sic) Stir well then sprinkle a little meal over the mash let it stand 5 days that is 3 full days betwist the Day you mash and the Day you cool off – on the fifth day put in 3 gallons of warm water then put in one gallon of Rye Meal and one gallon of malt work it well into the malt and Stir for 3 quarters of an hour then fill the tub half full of Luke warm water. Stir it well and with a fine sieve or otherwise Break all the lumps fine then let it stand three hours then fill up the tub with luke warm water.
For warm weather – five Bushels of Slop Instead of Six let it stand an hour and a half Instead of three hours and cold water Instead of warm.
A Receipt for Destilling (sic)
By Sweet and Sour Mash May 18, 1818”
Interestingly both of these recipes are actually forms of sour mash with similar and yet quite different aims. The notated “sour mash” recipe does resemble closely what is done in Kentucky in modernity and is very similar to what Dr. Crow was notable for doing above. The sweet mash recipe however is similar to distilling methodologies practiced by moonshiners and distillers the world over who are reliant on using wild yeast or reusing the same yeast strain repeatedly for consistency or practicality purposes.
In many old sour and sweet mash recipes you will see reference to the use of “Slop” or spent mash/stillage as a replacement for yeast and some recipes even call for the slop to be held in tubs for several days at a time giving it time to cool off before being added to a newly made fermentation. Here is where having an understanding of what spent mash/beer is capable of and actually does in a fermentation becomes paramount to having a true understanding of “Sour Mash” whiskey production. The key to opening the door on both methodologies is related to both yeast and the conditions that govern their health and allow them to propagate efficiently and quickly and also allow for other reactions caused by beneficial bacteria (and the conditions they are propagated within). All of which we will come back to, but first, let us right a historical wrong.
While Catherine Carpenters “Sour mash” recipe is the earliest recorded in Kentucky, it is in fact not the first recorded in the United States. That honor as of this writing goes to Michael Krafft in his book “The American distiller, or, the theory and practice of distilling where he lays the method out in Chapter 11, Of mashing and fermentation as follows:
“Various deviations have been adopted with tolerable success. The plan of cooling off with the liquid part of the returns, or what is termed pot ale, has advantages, it serves the purpose of producing a powerful and rapid fermentation, though tolerably perfect: this practice has been adopted under an idea, (and I think a just one) that the still does not throw off all the spirit.”
This account, a full 14 years prior to Catherine Carpenter, was published in 1804. Shortly thereafter SAMUEL McHARRY, OF LANCASTER COUNTY, PENN penned a similar account in 1809 (a full 9 years prior to Catherine’s notation) from his book The Practical Distiller. As follows:
To make four gallons from the bushel.
This is a method of mashing that I much approve of, and recommend to all whiskey distillers to try it—it is easy in process, and is very little more trouble than the common method, and may be done in every way of mashing, as well with corn or rye, as also a mixture of each, for eight months in the year; and for the other four is worth the trouble of following. I do not mean to say that the quantity of four gallons can be made at an average, in every distillery, with every sort of grain, and water, or during every vicissitude of weather, and by every distiller, but this far I will venture to say, that a still house that is kept in complete order, with good water, grain well chopped, good malt, hops, and above all good yeast; together with an apt, careful and industrious distiller, cannot fail to produce at an average for eight months in the year, three and three quarter gallons from the bushel at a moderate calculation. I have known it sometimes produce four and a half gallons to the bushel, for two or three days, and sometimes for as many weeks, when perhaps, the third or fourth day, or week, it would scarcely yield three gallons; a change we must account for, in a change of weather, the water or the neglect or ignorance of the distiller. For instance, we know that four gallons of whiskey is in the bushel of rye or corn—certain, that this quantity has been made from the bushel; then why not always? Because, is the answer, there is something wrong, sour yeast or hogsheads, neglect of duty in the distiller, change of grain, or change of weather—then of course it is the duty of the distiller to guard against all these causes as near as he can. The following method, if it does not produce in every distillery the quantity above mentioned, will certainly produce more whiskey from the bushel, than any other mode I have ever known pursued.
Mash your grain in the method that you find will yield you most whiskey—the day before you intend mashing, have a clean hogshead set in a convenient part of the distillery; when your singling still is run off, take the head off and fill her up with clean water, let her stand half an hour, to let the thick part settle to the bottom, which it will do when settled, dip out with a gallon or pail, and fill the clean hogshead half full, let the hogshead stand until it cools a little, so that when you fill it up with cool water, it will be about milk-warm, then yeast it off with the yeast for making 4 gallons to the bushel, then cover it close, and let it work or ferment until the day following, when you are going to cool off; when the cold water is running into your hogshead of mashed stuff, take the one third of this hogshead to every hogshead, (the above being calculated for three hogsheads) to be mashed every day, stirring the hogsheads well before you yeast them off. This process is simple, and I flatter myself will be found worthy of the trouble.
Here lies the key to understanding “Sour Mashing” as it was originally conceived and for all of its uses and it tries again directly to yeast, but also to the inefficiency of starch to sugar conversion in old farm distilleries. As McHarry notes above, he is adding water back to the spent mash and allowing many of the solids to settle and is then transferring this spent “wash” into a clean fermenter (hogshead) wherein he utilizes it as a yeast starter for freshly made sweet mash after allowing the yeast to propagate. If in fact the beer was spent then how was yeast able to propagate itself in this hogshead of lower pH spent wash? Well, the beer was spent, and all alcohol was extracted from the spent wash during distillation, however due to the inefficiency of mashing in during challenging climatic conditions and generally in absence of a good thermometer, coupled with the fact that most if not all farm distillers of the time (Including most likely Catherine Carpenter) in the U.S were making their own and using their own corn malt as opposed to rye or barley malt (which was both much harder to procure and to produce on a small scale) and since corn malt has far less Diastatic Power (the ability to convert starch to sugar in grain) then the cooked mash retained a large proportion of unconverted starch which would subsequently be converted during its use in the succeeding fermentation and add to the yield which he accounts for. This also speaks for how inefficient fermentation by way of a standard “Sweet Mash” was at that time due to either weak yeast (we are getting close to explaining the remedy!) due to a lack of nutrients or an off kilter pH or due to the lack of temperature control on fermentation at the time (perhaps the yeast went dormant during a cold spell or died during high temperatures, or simply wasn’t attenuated to the higher specific gravity of the mash). Whatever the cause, there is more than enough sugar left in the matrix to create a yeast starter. The remaining starch in the water isn’t simply enough to account for the gain in yield from the subsequent fermentation, however the health of the subsequent generations of yeast is!
One of the biggest constituents found within spent mash is autolyzed yeast, essentially dead yeast husks. These dead yeasts are excellent sources of nitrogen which yeast needs to thrive but also create an environment conductive to yeast propagation as they provide surface area for the yeast to cluster and then bud. They represent a source of yeast nutrition that is not often available (at least not in large amounts) in simple sweet mash whiskies and which give the yeast a major boost in metabolism to make their way through those sugars in order to convert them into alcohol and C02 and which accounts, at least in part, for the gain in yield experienced by the distiller. In fact, modern pre-prepared yeast regiments are made primarily from these dead yeast “hulls” and if push came to shove and marketing departments were truthful, most of the current crop of “sweet mash” producers are probably using some of these alternatives.
It is of course unlikely that McHarry or Carpenter or Krafft at the very least knew this is what was happening in their fermenters, but what they certainly knew was that fermentations utilizing this method were far more productive and likely were infected by unwanted bacteria far less often. The other thing they were certainly well aware of (just like Dr. Crow) was just how inefficient their mashing was at converting starch to sugar. Using some proportion of the spent mash (I’ve seen examples up to 50%) made simple economic sense as it allowed them to recover some of the lost and unconverted starches in the next batch, but it also did a lot of other things.
One of the effects would have been the buildup of complex esters and long chain fatty acids caused by chemical breakdown facilitated by heat in the wood fired pot stills. Subsequently and arguable leading to the most important factor in distilling: More Flavor!
Of course, this would have also have corrected the pH to something more suitable for the yeast as well (although yeast can do this themselves which we will talk about with sweet mash momentarily).
Now, on occasion I have seen reference to this spent beer/mash being “suffered” as they call it to stand in a tub for many days before it is added “cold” back to a newly mashed in fermenter in place of yeast, in fact this was very common up until prohibition. Usually in these accounts small amounts of fresh beer/wash are “fed” to the spent wash in order to facilitate its “fermentative prowess”. What is happening here is still a form of sour mash, but the level of complexity and subsequently the “involvement/understanding” of the distiller is heightened. This is very similar in point of fact to how a yeast jug (or Dona Jug) was used to propagate yeast and subsequently dose fermentations with an active live culture, it’s also very close to a sour dough bread methodology and probably where “sour mash” got its name and connotation from.
In these cases, you are creating vats of low pH spent mash in your distillery and allowing them to hang around and pick up only the absolutely strongest strains of yeast and beneficial bacteria that will survive in that environment. You are in essence creating a self-selecting yeast starter that favors the organisms you want to both ferment and subsequently transmute your raw material into the finished beer/wine for the still. These conditions are incredibly efficient for picking up highly selected and efficient yeast strains but also malolactic bacteria. Malolactic bacteria are used by many distillers for the conversion of malic acid which can be “sharp” to lactic acid which is considered softer and “creamier” on the palate. Malolactic bacteria are also incredibly adept at going dormant in low pH environments and coming back to “life” when the pH is increased. In many other distilling cultures (rum, Scotch) these “co-inoculants” are much better understood and utilized as a part of terroir and spirit “character” than they currently are in the U.S., but if you went back to the 1800’s in the U.S. each distillery using this sour mash method (or a Dona jug for yeast propagation even in sweet mash) would have certainly have had their own unique strain of yeast and malolactic bacteria.
So common were these methods that I would have no doubt that the very yeast strain that Jim Beam captured from his porch in Bardstown Kentucky during prohibition and that was subsequently divided between Heaven Hill and Makers Mark in later years most likely evolved in and was a product of one of these distilleries. Nothing about the environment of Kentucky or Indiana or Pennsylvania, or Maryland is unique for the production of yeast specific to distilling other than the fact that all have a distilling tradition with some parallel that makes the selection and propagation of wild yeast with specific traits incredibly efficient and would have made such strains far more prevalent (dormant or not) in the surrounding air, water, wood, etc.
While I have not yet discovered evidence for the earliest of “sour mashing” in grain distillation I do have every honest belief that like many of our distilling methodologies it too can be traced back to the old world. Many of our grain whiskey practices are analogous to what Dutch and German distillers were practicing with raw and unmalted grain whiskey productions and I fully suspect that we Americans simply brought those methodologies with us into our distilleries via heritage or adoption.
Now, before moving on to “Sweet Mash”, there is yet another version of sour mash we need to explore. This sour mash is related again to yeast propagation, yeast nutrient, and pH levels but is handled a little differently and is commonly only used in current practice by home distillers. This version of sour mash sees distillers who distill only from a “wash” (liquid only, no solids) remove said wash from their fermenter to their still and subsequently distill it in whatever way they prefer. The “trub” or “lees” left behind in the fermenter is full of both dead yeast as well as dormant yeast (who stopped performing due to a lack of fermentable sugar) and leftover grain (sometimes already nearly exhausted and sometimes never converted to begin with in the case of a “sugar head” whiskey). From this bed is removed an amount of grain and to it is added new grain and water (and sugar quite often). The bed provided the needed yeast that was once dormant as well as unconverted sugar and helps again to lower the pH for the subsequent fermentation. In an uncooked mash (a mash that relies on refined sugar for alcohol) the unconverted grain is slowly “cold” hydrolyzed and releases flavor into the liquid matrix. If enzymes are added in the form of exogenous or malt derived sources the starches slowly convert to sugar. Sometimes these mashes are carried on for many generations by simply scooping out some amount of spent “trub” and adding new grain.
Many folk distillers would perform a similar task during prohibition. They knew their starch to sugar conversion was poor when making a whiskey the traditional way with a cooked mash so would take the spent grains and wash and put them back in a fermenter while hot and into which they would add refined sugar and malt to extract the remainder of what was left for a subsequent run.
The advent of yeast nutrients, temperature control, exogenous enzymes, lab standardized yeast, and standard chemistry equipment in many modern distilleries has led many to give up the traditional sour mash method, and of those who still practice it I’m not sure how many of them truly have an understanding of its original intended uses. Many have switched to the use of citric acid for souring and of the larger distilleries that use the sour mash method I would place a bet that it is done from an energy saving perspective as opposed to a true quality control perspective, as using the reclaimed heat from the spent mash to cook a fresh mash makes a lot of economic sense and represents a valuable resource. That said, the tradition does live on in many small distilleries and home distilleries. The other branch of sour mashing I didn’t mention previously is involved in the production of fruit brandies. Although brandy doesn’t have the marketing association with sour mash that American Whiskies obviously do, many traditional European folk distillers will add 10-15 percent or more spent wash into their new make fruit wines for all of the reasons mentioned above. This drops the pH as mentioned and is known to create a more aromatic wine for distilling with a sharper and more fruit forward nose and acidic “bite” on the palate of clear brandies.
Many modern distillers will also use selected strains of lactobacillus to sour their whiskey mash as well, similar to what was discussed above in the old methodology. In early distilleries there were a handful of other methods for souring a mash as well that were non-reliant on spent mash, including the use of citrus juices (where available) and hops. Many times, hops were used for their antimicrobial properties in conjunction with the pH of liquid yeast cultures but in some distilleries, they were also a viable component of water for mashing in. The hops would be added to the water boiler as the water was heated and would imbue the “strike” water to be used in the cooking process. This would also create a slight flavor variation in the finished whiskey as the volatile components of the hops would distill over into the product.
Now onto sweet mash. As classified above any whiskey made without the addition of backset (or other pH corrections) or not fermented on a bed of spent grain/trub/lees would be considered a sweet mash. In the days before temperature control in fermentation and intense sanitation sweet mash whiskeys could certainly be a true challenge to make due to the threat/risk of bacterial contamination, this is still a problem with many home distillers. The modern distillery is equipped with any number of ways to combat such issues and the risk in most current settings is quite mitigated.
Prior to prohibition many “sweet mash” whiskeys were sold at a premium as the issue at hand and the challenges of creating a sweet mash were very well understood. The taste, as one might imagine is a little different as well. Usually a sweet mash whiskey will be a little cleaner and less heavy bodied than a sour mash whiskey and will subsequently drink a little more linear, with a clearer and sharper focus on the raw material in the fermentation and its virtues, although there are exceptions. Some will use the various methods of correcting pH above (citric, malic, lactobacillus) to stave off bacterial infections, but many will run a true sweet mash. There is no set pH that all distilleries abide by as a starting point as all grains and water sources as well as the amount of grain in the matrix will allow pH to vary but these whiskeys usually start between 5.2 and 5.5. Of this we will return for discussion momentarily after a little historical aside.
Everyone, I presume, is aware of the “Lincoln County Process” and its most famous practitioner Jack Daniels. Jack Daniels of course itself is a “sour mash” whiskey from Tennessee, but were you aware that the Sour Mash process was an important signifier alongside filtration through maple charcoal of the “Lincoln County Process”? What most don’t know is that there was another wide spread process named after yet another county in Tennessee as well that relied on using a “sweet mash”; The Robertson County Process. All things being equal, the R.C. process relied on sweet mash and charcoal filtration and the whiskey subsequently made herein was often sold and served unaged. This style of whiskey was actually pretty preeminent in Kentucky and Tennessee overtop of the more common aged bourbon and Lincoln County Process whiskey prior to prohibition. Prohibition of course virtually wiped its production off the map except upon moonshiners of the region who often made sweet mash whiskeys that were filtered through charcoal before sale.
Coming back around to the science of sweet mash there are a few notations worth mentioning. Typically beer fermentations for whiskey production are fairly short at 3-6 days (although I do know of instances in less than ideal conditions requiring 10-14 days), this is a fairly short window of time and good selected yeast will ferment hard during most of this period, meaning that enough C02 is being pushed from out of the top of an open topped fermenter that very little in the way of bacteria ever has a chance to inhabit the vessel and the subsequent ferment and ruin it. The yeast of course as well, if it has good nutrition, is typically of a strong type and outcompetes most any wild yeast or bacteria (although there are exceptions), but the process of fermentation itself will actually sour a mash of its own accord. As the yeast breaks down sugar and turns it into ethanol it begins to become stressed by its own waste material (alcohol) and will actually begin to turn that alcohol (without the presence of acetobacter) into volatile acidity, lowering the pH, in a last-ditch effort to survive the “yeastpocalypse” that is coming. Effectively creating its own “sour mash” These acids of course make up a large percentage of the flavor profile of any distilled spirit.
Going back into the history of the sweet mash methodology we will also take note of the methodology mentioned above of pitching yeast from a previous ferment which would have also have historically have played at role in adjusting the pH of the fresh mash depending of course on how much volume was added from the previous fermentation. This in itself would to me be considered still yet a form of making a sour mash. In a previous article we discussed the use of the old-fashioned Dona Jug (Yeast Jug) amongst distillers. These yeast jugs always relied on a portion of spent mash or finished/fermented mash to be a carrier for yeast nutrients and viable cells in order to keep the yeast strain alive and healthy across countless generations by way of pH adjustment, depending on the pitch rate of this liquid yeast (between 2-6% amongst traditional distillers) and how far into fermentation the liquid yeast was, it is arguable that a pH adjustment was also affected by this method.
It is also important to remember that one of the most viable natural sources of lactobacillus bacteria is present in nearly every distillery and every whiskey mash; malt. Since we don’t typically add malt to a mash until the cooldown side of the cooking process between 135-148 and since this isn’t hot enough to kill the culture, it is likely that some level of lactobacillus bacteria survives the cook and also contributes to the drop in pH seen in sweet mashes.
I have made and drank many fantastic sweet mash and sour mash whiskeys and truthfully I think both are valuable tools in the distillers arsenal, I couldn’t say with any amount of certainty that I believe that either method makes a better product, much like the discussion of differing types of stills it truly depends on the raw material and the preference of the distiller in terms of the type of product that they wish to make at that moment in time. I do think that the large distillers and many undereducated distillers have made far too much of the sour mash process in terms of quality in their marketing materials over the years and I do think that most have only a vague understanding of the historical use of the process as anything other than a way to adjust pH or to regain/reclaim heat for the cooking process. I hope this article has shed some light on both methodologies and their history for readers, there are some other distilling parallels in the world that have some interesting similarities including the use of “muck” and of dunder in the rum world which I believe that whiskey distillers could easily draw some knowledge and application from as some of the process are far more developed that our current understanding of the use of spent stillage and hold the potential to unlocking some amazing flavor profiles that we have not yet experienced.
Distilling is a humbling art and the more I learn the less I seem to know. I hope that never changes on my behalf.