Distillery Practice—Mashing

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A very unique mimeographed manuscript crossed my desk that was penned by a Seagram employee, likely in the late 1930’s or early 1940’s, but before the famous 1943 Seagram text called “Fundamentals of Distillery Practice” (abbreviated here as FODP) written by Herman F. Willkie and Joseph A. Prochaska. The manuscript came to me from an individual who wanted to contribute to the education of the new generation of distillers.

The manuscript contains a much different framing than the widely read 1943 text and represents an information gathering phase before much of Seagram’s own research was conducted. We see rye only being infusion mashed which was the tradition the author likely observed in the industry before the idea that rye could be pressure cooked like corn as presented in FODP. The author notes right away that mashing is about to see a revolution in both understanding and practice. Concepts are outlined, but many specific parameters are left out and I tried to add them as best I could from FODP so readers can get a sense of numbers that frame the processes.

pH is frequently discussed, but it is also just an emerging concept at the time and no doubt key to understanding the active components of pre-prohibition techniques, especially regarding the handling of rye which is known to become overly viscous and foamy to the point it can be unworkable. The author presents what I think is the earliest description of what is now discussed as SSF or simultaneous saccharification and fermentation which in this particular context relates to the idea that 10-20% of the potential fermentable sugar needs to undergo saccharification during the fermentation stage and this will have a bearing on mashing strategy.

Something absent is description of specific mashing processes for yeast mash which is the percentage of the of the total grain bill devoted to growing yeast and traditionally made up of small grains like rye and malt for their nutritive properties. This is not widely discussed in our current direct pitch era. It may also have been somewhat forgotten because of other practices that came about mid century such as growing yeast via line mashes that are the same as the total mash bill. However, the old practices may be key to high value congener formation and worth revisiting.

Something brilliant that many may rationalize away as obsolete for favor of easy to use exogenous enzymes is the idea that you can carefully step mash rye to first induce protein splitting followed by further temperature steps with rests that target one amylase enzyme before the other to pull maltose from the starch in an order that somehow leads to a lower viscosity than if both enzymes are active simultaneously. When this is coupled with an ideal pH, the process may sum up the majority of the pre-prohibition wisdom on mashing rye. What isn’t spelled out is the practical magnitude. Does this still need to be processed on a three chamber still or can you achieve a mash of nothing but rye and malt that can be run through a typical continuous beer still?

To be honest, I am no expert on this topic and am not currently too aware of what exactly large producers or small new American producers practice as rye is having a revival. My understanding is that nearly all producers favor exogenous enzymes and there is probably no going back even if traditional practiced are better understood. I wold love some feedback if anyone finds any information here novel, especially if you’ve already tried to digest FODP.

Many passages I deemed important are in bold as well as my own comments so that if you are skimming the text, you may quickly find some good stuff.


Mashing is in a greater state of flux, both with regard to practice and theory, than any other distillery operation. Indeed, we may speak with less assurance with regard to mashing than to any other phase of the process. This is a rather strong statement when we consider that it is made in connection with an industry which at present, especially in our case, is undergoing constant and drastic revision. However, with regard to mashing we are faced with the possibility of such drastic change both in practice and theory that many of our present concepts may be out-moded within the short period of perhaps a year. Much of the theory in regard to mashing which is now considered axiomatic and which has been incorporated into practice for generations, will unquestionably be proved entirely, or in part, false.

Mashing consists of two essential steps designed to change the grain starches into sugars which will undergo fermentation. The results of the fermentation, both as to yield and quality of spirits produced, is to a considerable extent, dependent on the success attained in the mashing operation. The raw starch as it exists in the grain will not undergo fermentation. In fact, in this state the grain starches will not undergo the bio-chemical conversion to fermentable sugar without first bringing about a change in the physical state of the starch itself. We are obliged then to consider the physical preparation of the grain starches as well as the bio-chemical reactions which then become possible.

Mechanical disintegration of the whole grain, by milling, produces a course subdivision of the kernel, but, no matter how fine the grind, the starch particles are still far too large in size to permit successful conversion. The grinding of the grain to meal is merely a step in preparation for a more severe physical change of the grain starches to a much higher state of subdivision. This alteration is brought about by subjecting the meal, in the presence of water, to a temperature which is sufficiently high to cause the starch granules to expand and burst. The bursting of the starch granules is called gelatinization temperature. In the whole grains and ground meal each tiny starch packet or granule is separated from its neighbors by a cellulose-like material which surrounds it. Upon gelatinization the protective membranes are broken and a large starch surface area is exposed. Thus, our purpose in cooking becomes apparent, that is, to achieve as high a degree of starch fineness as possible in order that the saccharification reaction will take place readily. Some idea as to our success in achieving this objective may be gained from an example which is not meant to be accurate quantitatively, but merely to illustrate this point. Let us assume that it would be possible to measure the surface area of all the starch granules in a grain of ground meal. We should probably find that the combined surface area would total less than a square yard. However, if we then gelatinized the same quantity of starch it is probable that the exposed surface area would then be sufficient to cover an acre or so. This simple example illustrates the magnitude of the physical changes which occur to the starch granules on cooking.

The second step in mashing, conversion, is more spectacular than cooking since it involves bio-chemical reaction rather than physical change. The principal change, saccharification of sugar formation, involves the reaction between starch and water. Such a change, that is a reaction with water, is known as hydrolysis. We write the reaction:

The sugar, maltose, which is the principal product, may itself react with water to give the sugar glucose, C6H12O6, and from this we infer that starch is composed of a large number of glucose molecules chemically combined to form a large molecule of varying molecular weight. For each 162×2 pounds of starch, 18 pounds of water react chemically to give 342 pounds of maltose. The sugar, maltose, is related chemically to table sugar, sucrose, and in pure form has much the same appearance as well as a similar taste.

The reaction of starch with water may be brought about by the catalytic action of dilute acids or under the influence of hydrolytic enzymes. When dilute acids are used to catalyze the reaction, maltose or glucose may be formed depending on the conditions. Since in the production of whiskey and grain neutral spirits enzymes are used exclusively, we will confine our discussion to enzymatic hydrolysis.

Enzymes may be regarded as catalysts of biological origin which are formed in all living cells. They enable the cell to carry out the chemical processes necessary for its existence at a sufficient speed and at temperatures much below those that would be required in the laboratory. A given enzyme will react only on a single substance or group of closely related substances. In the case of enzymes acting on carbohydrates, this specificity is extreme, one enzyme acting on one carbohydrate only. The quantity of enzyme necessary to bring about a reaction is usually very small. In the case of some enzymes, over a million time its weight may be acted on by the enzyme.

In mashing the principal enzyme involved is called amylase. This enzyme acts on starch to give fermentable sugars.

The necessary enzymes for conversion are supplied by malted grains with malted barley being by far the most commonly used. However, any cereal grain may be malted and utilized for this purpose. In fact, an extract containing the necessary enzymes would serve the purpose just as well. Even unmalted cereals exhibit a certain degree of enzyme activity. However, after malting this property is greatly increased.


There are two general methods of carrying out the mashing process. The first consists in cooking the meal in water at a high temperature to bring about gelatization, cooling to the conversion temperature, and adding the malt. This is the usual procedure in mashing corn. In the second procedure, the gelatinization and conversion are brought about at the same time without resorting to high temperatures. In other words, the meal and malted grain are added together and heated to the conversion temperature and held for a suitable period. In this method the mash is not subjected to a boiling temperature. Such grains as rye, wheat, and mixtures of malted grains are usually mashed in this way. [This lower temp process, I believe, years later gets called infusion mashing]

Presumably, in either case, the purpose is to achieve the greatest degree of starch conversion. By conversion is meant the hydrolysis of starch to maltose and dextrines. However, it is somewhat difficult to define a purpose for mashing which is not correlated with the major objective, that is, the production of alcohol from the fermented mash. In other words, we should not consider a conversion good merely because a major portion of the starch has been converted to sugar. After all, we are not marketing maltose and it is merely an intermediate in the process. It might be better to speak of a good conversion as one which has contributed to a maximum yield of alcohol of high quality. Using this definition, we could logically speak of a conversion as being good in which the percentage of maltose is quite low. This reasoning hold throughout the process. A grind, for example, may give a screen analysis in exact accordance with production instructions but unless this grind is the most satisfactory so far as alcohol production goes, we should not be justified in calling it good.

Utilizing our present procedures, there appears to be a maximum of maltose which may be formed from the starch. This highest quantity of maltose is in the neighborhood of 90%. The remaining converted material is in the form of dextrines. The dextrines may be considered to be intermediate between maltose and starch. That is, the dextrines represent an incomplete or partial hydrolysis of the starch molecule.

Starches and dextrines will not undergo fermentation and it is essential that they be converted first to maltose before fermentation can take place. Since in even a complete conversion approximately 10% of the starch remains as dextrines, we must consider a so-called “secondary conversion” which in reality is the conversion of dextrines to maltose within the fermentation tubs. Hence, 10% of the starch, in the form of dextrines, undergoes conversion to maltose in the fermenters. This conversion must, of necessity, take place at a much lower temperature, from 65-90°F., and the conversion must be completed within a period of 72 hours. Also, since the conversion of starch or dextrines takes place under the influence of enzymes furnished by the malted grain it is essential that an excess of amylase be present in the fermenter to bring this hydrolysis about. The fact that such a high percentage of hydrolysis does take place within the fermenters is highly suggestive and thought-provoking.

[Is this the first time in American whiskey literature it is recognized that over 10% of the dextrines need to be converted during fermentation? Present day, this territory is called SSF or simultaneous saccharification and fermentation. The author is confining fermentation to 72 hours which may just regard economy bourbon. Many ferments surveyed in the 1960’s were going as long as 120 hours (5 days). My understanding is that some of these long durations were mashes that were let go through the weekend. Some present day rye whiskey ferments are dragged out to 5 to 7 days to minimize foaming.]

Besides the enzymes which bring about the conversion of starch to maltose and dextrines, the amylases, there are also innumerable other enzymes which bring about the hydrolysis of protein material with the resulting formation of a considerable number of nitrogen-containing materials. This splitting of the protein by enzymatic action furnishes soluble nitrogen substances which serve as yeast food during fermentation. These nitrogen products also have a decided effect on the quality of the product. Here is another case where we may be led into a blind belief, based on logic, that the greater the protein splitting the better. This may be true; however, there is surely some limit to the insatiable appetite of even a yeast cell. For this reason we should certainly consider the advisability of controlling protein hydrolysis with the same care that we attempt to control amylase activity. Could it not be that we should really inhibit rather than encourage proteolysis or protein splitting?

[I would love to learn present day thought on this topic. Would the idea equally apply to corn and rye mashes? Regarding corn, the author could be suggesting that protein splitting be avoided as an objective because it requires energy intensive high temperature pressure cooking and instead ammonia salts could simply be added. This could suggest that like traditional Jamaica rum, no ammonia should be added to pre-prohibition styles of Bourbon.]

Mashing should not be considered as merely a means of changing starch into fermentable sugars and protein into soluble materials since it also furnishes the means of sterilizing and pasteurizing the mash. Our present grain specifications allow bacteria counts as follows:

Grain                    Bacterial Count

Corn                           500,000
Rye                          2,000,000
Malted Barley          5,000,000

These figures represent maximum allowable bacterial counts for these grains. From them we infer that malted barely contains in the neighborhood of ten times as much bacteria as corn. Grain which has been pressure-cooked will be free from bacteria. The temperature achieved in pressure cooking is sufficiently high to destroy all vegetative forms of bacteria as well as their spores. The hot, sterile corn mash is then cooled to the converting temperature and the malted barley added. In a spirits mash about 10% of malted barley is used having approximately ten times as many bacterium as the corn meal. The conversion temperature may in no case be considered sufficiently high for sterilization. Therefore, our gain starting with sterile corn mash may not be considered of overly great consequence. However, of this, we cannot be too certain since our present knowledge of the effect of certain types of bacteria is not extensive. In fact, the Research Department currently is carrying on work to determine the types of these bacteria and their effects on spirit production. The results of this work may have considerable influence on both future grain specification and processing methods.

[It will be interesting to see if we can find signs in the later literature of changing thoughts here. It appears we can say that certain grains are more important to establishing microbial terroir than others.]

A similar problem arises in the second method of mashing customarily used in converting such grains as rye and wheat. In this method the maximum temperature is equivalent to the conversion temperature used in mashing corn. This temperature, 145°F, is just sufficiently high for pasteurization but does not approach the minimum temperature for sterilizing. For this reason none of the grain is made sterile using this process. We must therefore, in all cases, depend upon pasteurization to destroy, if possible, all vegetative forms of bacteria but not their spores.

[Don’t forget that lower temperature pasteurization is a function of temperature and time, so sufficient duration at temperature is important. At 145°F I’ve seen data that claims a 5 log reduction in microorganisms in as short as 3 minutes and vaguer data that claims 30 minutes.]

In addition to these problems, the viscosity of the mash must be taken into account. In order to facilitate such subsequent operations as pumping and cooling, it is desirable to obtain the greatest possible lowering of the viscosity. The preparation of the mash should also be such as to eliminate, so far as possible, foaming during fermentation. These problems are particularly obnoxious in rye mashing. Most of the factors mentioned above are influenced by the degree of acidity or pH. Therefore this factor must be taken into account.

The principal mashing objectives may then listed as follows:

1. Control of amylase activity in order to obtain a good conversion.
2. An excess of free amylase must be present in the converted mash to take care of conversion of dextrines in the fermenter.
3. Control of proteolytic or protein-splitting enzymes.
4. Control of bacteria in the fermented mash.
5. Lowest possible viscosity essential.
6. Lessing of foaming characteristics.
7. Control of pH.

[Limiting protein splitting may also be considered from the perspective of the dried grains as a valuable byproduct.]

Gelatinization – The temperature at which gelatinization takes place is of considerable importance. Gelatinization occurs upon the bursting of the starch granule due to subjecting the meal to sufficiently high temperatures. Gelatinized starch undergoes rapid conversion while conversion of raw starch is extremely slow. Approximate gelatinization temperatures for various types of starch are given below:

Amylases – The enzyme amylase consists in reality of more than one enzyme. For the sake of simplicity we shall refer to this group of enzymes as amylase (the term “diastase” is also used). Amylase has two principal properties due to individual amylase enzymes. The first property is the so-called “solubilizing effect” which alters the gelatinized starch to a soluble form. The second property is the ability of amylase to bring about the saccharification of starch. The liquefying power of amylase is at an optimum at 158°F. While the optimum temperature for saccharifying is at 120-131°F. As the temperature is increased the action of all enzymes increases. This increase in temperature, along with the increased action of the enzymes brings about their deterioration. For example, the amylase in barley malt completely loses its saccharifying power at 158°F. and its liquefying power at 180°F. For this reason the optimum temperature should be considered as the temperature at which the deterioration of the enzyme is balanced by the hastened splitting of the material undergoing hydrolysis. However, in fixing the conversion temperature another factor must be taken into account. That is, the inhibiting of bacterial growth. For this reason the conversion temperature is usually fixed at about 145°F., which is high for saccharification, but which does permit pasteurization of the mash. Hence, we may consider this temperature as the best compromise between time of conversion, enzyme destruction, and suitable pasteurization temperature.

[The idea of “pre-malt” is presented on page 38 of FODP and harnesses the fact that the liquifying temperature of amylase is higher than the saccharifying temperature. A small amount of malt is used to maximize solublizing to reduce viscosity, but avoid saccharification which would eventually lose sugars to carmelization during pressure cooking. Amylase is used in this narrow context then sacrificed during cooking. I have a feeling this is for economy practices with more concentrated mashes where volume and steam savings outweigh the cost of the malt. I have heard that easy to use solubilizing enzymes are commonly used instead of pre-malt for both small scale and large scale productions. I’m not aware if they operate on the same temperature guidelines.]

Protein splitting – The splitting of proteins is referred to as proteolysis. Insoluble proteins have little value as yeast food. The more soluble proteins do have value as yeast food while the amino acids and ammonia and its salts are excellent for this purpose. Certain enzymes present in the grain cause the splitting of protein into forms which may be utilized by the yeast cell. Suitable conditions for splitting of various materials present in grain are listed below:

Cooking procedure

Two general methods are used in cooking depending upon the type of grain mashed. The first procedure involves heating the meal and water under pressure to a high temperature prior to conversion. Any mash heated above the boiling temperature of water should be considered as belonging to this class. Corn is most commonly mashed under these conditions.

The second general method consists in heating the meal and water together with the malted grain to a temperature below boiling. Obviously, in this case, gelatinization and conversion take place simultaneously. Rye, and other small grains are usually mashed in this way. However, it is possible, and feasible to mash small grains using higher temperatures as in the first method, though not common in practice.

[In FODP on page 42, it is presented that small grains like rye can be pressure cooked which may result in protein denaturation creating a lower viscosity and absence of foaming in the ferment. However, enzymes are destroyed and it has substantial steam requirements. It is also mentioned that the same thing is not observed for wheat and for some reason pressure cooking increases viscosity.]

Pressure cooking – The procedure followed in cooking any grain under pressure involves a similar cycle. The desired quantity of water is drawn into the cooker and the meal added. During the addition of meal and subsequent mashing operations, agitation must be supplied continually. The mixture is then heated rapidly, under pressure, to the maximum cooking temperature which is merely the highest temperature to which the mash is subjected. The mash is held at this temperature for a pre-determined time and then cooled by releasing the pressure to atmospheric followed by the application of vacuum to still further reduce the temperature. The vacuum is released upon reaching the proper temperature and the malted grain added. The addition of malted grain, usually barley malt, takes place in one of two ways. The malted grain may be placed in a pony masher containing water and held at a temperature of about 90°-100°F. prior to adding to the cooker or it may be added by means of a suitable mixer depending upon the equipment in use at the plant. After addition of the malted grain the cook is immediately transferred to a drop tub or converter where it is held during the conversion period.

[On page 40 of FODP, it is mentioned that the pH of converted corn mash cooked in a batch pressure cooker is pH 5.0-5.8 as opposed to 5.8 at atmospheric pressure and 6.0 in a continuous pressure cooker. In the appendix, page 171 of FODP the high temp is held for five minutes and other parameters are shared.]

Atmospheric cooking – Ordinarily such grains as rye are cooked at atmospheric pressure. The desired quantity of water is drawn into the cooker at a temperature between 95°F. and 100°F. The agitator is started and the malted barley added and held for from 15 to 30 minutes. The rye is then added slowly to prevent ball formation. The temperature is raised to about 130°F and held for a period of time after which it is heated to 145°F. and then transferred to a drop tub or converter for the conversion period which is about equivalent to the combined holding time of the mash in the cooker.

[Some timing hints are given here and we see that the step mashing may have three phases. Barley by itself starting at 100°F, then with rye at 130°F (30 minutes FODP), then finally at 145°F followed by a duration in a drop tub. These numbers differ from what many modern beer brewers are using for their “protein rests” where a duration at 98–113°F is used to break down beta-glucans which cause a degree of the gumminess.]

[Another unique hint to reducing viscosity, FODP page 44, is that if beta amylase is targeted at 130°F and removes maltose units from the starch molecule, dextrines produced at later conversion at 145°F by alpha amylase may be smaller in size and of lower viscosity. So just like pre-malt harnesses a differential of activity, another can be harnessed here and no doubt modern temperature control gives us an advantage in harnessing it.]

[Another unique idea to consider regarding bacteria counts is presented on page 42 of FODP:

Because a great many bacteria are destroyed during the extended heating period in mashing, the bacterial count in wheat and rye mashes may be lower than in pressure cooks converted by malt.

This is slightly counter intuitive.] 

Conversion procedure

There is very little to say with regard to conversion procedure. Where the grain is pressure-cooked the mash is transferred to a drop tub or converter immediately after the addition of malt. This means that the greater share of conversion take place within the cooker rather than in the converter. In either case, the purpose of the converter or drop tub is merely to relieve the cooker for further use.

Mashing variables

The factors influencing the mashing of corn and rye will be considered separately. Corn, as pointed out previously, is heated to a high temperature under pressure prior to saccharification with malted barley while rye is not subjected to such treatment.

The chief variable factors to be considered in the mashing of corn are:

1. Particle size of meal [FODP provides no particle size but lots of equipment parameters, especially in the appendix.]
2. Maximum cooking temperature [308°F. is noted earlier. 310°F. is specified in Fundamentals of Distillery Practice page 38.]
3. Cooking times [These are not spelled out and no doubt related to the abilities of equipment.]
(A) Time of heating to maximum temperature
(B) Time of holding at maximum temperature [5 minutes if as high as 310°F.]
(C) Time of cooling to conversion temperature [“Blown” down to 212°F by releasing pressure, then reduced to 152°F by pulling a vacuum. Based on how long it takes to release the pressure safely in an autoclave, I assume this takes 15+ minutes.]
4. Conversion temperature [FODP 145°F]
5. Conversion holding time [FODP page 41 introduces the idea of “flash conversion” where the minimum time is used to juggle both pasteurizing the malt while preserving enzymes for secondary conversion.]
6. Amylase activity
7. Dilution [Historic 1960’s data for gallons/bushel]
8. Protein splitting
9. pH [FODP 5.3-5.6 which is between optima for both amylases.]

[Here, we are considering a pressure cooked process, but just as a contemporary reference, I have seen description of a 40 minute cook time for corn at 190F. I have no specific first hand experience with pressure cooked corn, but a colleague who does feels it produces off aroma.]

Particle size of meal – The ease with which gelatinization takes place is partly dependent on the particle size of the meal. A larger particle size may be used when high temperatures are employed. A coarse grind has the advantage of allowing easier dried grain recovery.

Maximum cooking temperature – The highest temperature used in cooking is called the maximum cooking temperature. This temperature, which is above 308°F., greatly exceeds the temperature required for the gelatinization of corn starch. An increase in the cooking temperature results in a lowering of pH, the pH being lowered by about 0.1 for each 15°-20° F. rise. We are unable to state definitely whether the maximum cooking temperature or the length of time that the mash is maintained above a certain datum temperature is the more important.

[On page 40 of FODP, it is mentioned that the pH drops because of protein decomposition and resultant acid formation. It is also mentioned that this pH drop should be monitored because if too significant it may interfere later with malt conversion.]

[The 308°F. pressure cooking temperature figure is noted by J.A. Wathen in Distillery Operation and Control, 1909 so it is a pre-prohibition concept.]

Cooking times – The cooking times are the time of heating to the maximum cooking temperature, the time held at this temperature, and the time of cooling to the conversion temperature. If the maximum cooking temperature is sufficiently high no holding is required at this temperature.

Conversion temperature – The conversion temperature is a compromise between the optimum temperature for liquefying and saccharifying of starch and the minimum temperature required for pasteurization. The corn mash, after pressure cooking, is sterile. However, upon cooking to about 145° F., the non-sterile malted barley is added. Hence, the conversion temperature must be sufficiently high for pasteurization of the malted grain.

Conversion holding time – The time of holding for conversion unquestionably is open to debate. No matter how long a period the mash is held at this temperature, complete conversion to maltose will not take place. About 20% of the starch remains as dextrines and must be converted during fermentation. Apparently, an equilibrium exists between maltose and dextrines and final conversion of the dextrines will not take place until part of the maltose has been changed by fermentation to alcohol and carbon dioxide.

[The earlier 10% estimate appears to have risen to 20%? Would it be correct to say that the duration of a bourbon ferment has evolved to, at its shortest, be as long as it takes for that 20% to be converted during fermentation and then utilized (without extraneous enzymes)? In FODP page 41, it is mentioned that protection of amylase for secondary conversion is prioritized over high initial conversion.]

Amylase activity – The malted barley furnishing amylase activity should possess this property to a very high degree. In the first place there should be sufficient amylase in the converter to bring about maximum liquefaction and saccharification in the converter, together with an excess of amylase required for the conversion of dextrines in the fermenter.

Dilution – The dilution or concentration of meal per unit of water determines the concentration of sugar in the converted mash. Amylase activity is not affected over a wide range of concentration. For this reason, considerations of economy usually determine the quantity of water used per bushel of grain mashed. Obviously, steam consumption is decreased with decrease in mash volume. However, difficulties in pumping, cooling, and agitation are increased with increased concentration and these factors must also be considered.

[Gallons/bushel data is presented in this spreadsheet taken from a late 1960’s IRS paper.]

Protein splitting – Hydrolysis, or splitting of proteins, has been discussed.

pH – The pH has a decided influence on both protein-splitting enzymes and amylase. For this reason, it must be carefully controlled.

There are a number of reasons for not pressure-cooking rye before conversion. Firstly, rye mashes have a much higher viscosity and lower surface tension than corn mashes, properties which necessitate a different mashing procedure. Furthermore, even unmalted rye grain contains a very considerable diastatic power. Hence rye is seldom heated above the conversion temperature during mashing since high temperatures would destroy its diastatic power and would also result in foaming during fermentation. The variable factors to be considered in the mashing of rye are seven in number.

1. Particle size of meal [Much smaller than corn, especially if lower temperatures are used.]
2. Holding temperature [A step mash working up to a maximum temperature of 145° to pasteurize but not destroy enzymes.]
3. Holding times [Step mash starts with heating the malt, then a protein rest, then being raised to pasteurization temp. FODP page 46, notes that rye yeast mash may only be held at 145° for 20-45 minutes.]
4. Amylase activity
5. Dilution [Historic 1960’s data for gallons/bushel, but not clear pattern is established despite being recommended as higher than Bourbon]
6. Protein splitting [Practiced to reduce viscosity by holding at certain temperatures such as 98–113°F recommended by brewers. FODP, page 44, mentions “proteolytic enzymes” are active at 110-115°F and then that holding at 130°F for 30 minutes is practiced because other protein splitting enzymes are active at that temperature.]
7. pH [FODP notes the unadjusted pH of rye mashes is 6.0 and adjustment with stillage is desirable but not necessary.]

Particle size of meal – Due to lower mashing temperatures, rye is usually ground to a greater degree of fineness than corn. This greater fineness of grind, compensates, in part, for the lower mashing temperature.

Holding temperatures – As previously pointed out, the rye and malted mixture is heated to certain specified temperatures and held for varying times as the mash is raised to the maximum mashing temperature. This treatment, for some reason, results in a mash having a lower viscosity. The rather large time lapse between initial application of heat and final maximum temperature presumably is required in order to obtain complete conversion.

Amylase activity – Unmalted rye contains considerable amylase and, indeed, conversion will take place without addition of any malted grain. As in the case of corn mashing, an excess of free amylase must remain after conversion to take care of residual dextrines in the fermenter.

Dilution -Rye must be mashed with more water than corn because of its greater viscosity.

Protein splitting – Rye, among all grains, contains the highest percentage of soluble protein material. From this we may infer that in mashing rye greater control over proteolysis or protein splitting is necessary.

pH – The pH has a considerable effect on both viscosity and foaming properties of the mash. Hence, rigid control over pH must be observed. [Something to note here is that rye is better buffered than other grains so may require more backset to hit a desired pH.]

[We have been given hints about lowering the viscosity of rye whiskey mashes and transposed some parameters from FODP to the outline shown here, but what we haven’t seen is differentiation for regular mash and yeast mash which often represented 3-4% of the total grains used. Does yeast mash, optimized for growing yeast, see different parameters? If rye has enough enzymes for its own conversion, was malt featured in mash bills likely used primarily for yeast mash? Many pre-prohibition bourbons featured small grains like rye and wheat in their yeast mash before Seagram started developing economy processing utilizing “line mash” which paralleled the regular mash bill. Barley is a major feature of yeast mash because of its nutrient value. Other small grains are often featured because they provide nutrients that help natural souring of the grains. The initial pH may also have started higher than typical mash (before the addition of backset) to create suitable conditions for lactic acid bacteria growth.

An example of altered rye yeast mash processes is shown on page 47 of FODP. After being held at 145°F, the temperature is raise to 152°F for additional conversion with the strategy of having a high sugar content to suppress action by undesirably bacteria. There is enzyme loss, but that is not a problem because the temperature is often further raised to 160°F after souring to kill bacteria for a higher log reduction.]

[Something to note when comparing heavy rum fermentation to bourbon or rye where there is countless parallels is that grain ferments should not be conducted lower than a pH range of 4.7-5.0 because too low a pH would inactivate enzymes that must still convert a substantial amount of dextrines into fermentable sugar during fermentation (10-20%).]

[To return to J.A. Wathen in Distillery Operation and Control, 1909 (page 115), it is mentioned that yeast for Eastern rye’s are produced with a sweet mash of rye and malt that employs hops instead of lactic souring. If we go back to the historic 1960’s survey of mash bills, that would mean that only four of the ten rye’s are Eastern in style in terms of how yeast is grown. Numerous historic lectures follow Wathen’s that are worth knowing about and another from a Pennsylvania distiller operating a three chambered still contradicts Wathen and advocates for lactic souring of yeast mash. After American whiskey distillers started learning pure culture yeast growth at the very beginning of the 20th century, all of their traditional practices rapidly evolved and consolidated to a basic sour mash.]


Sanitation cannot be stressed too much. Cleanliness is an absolute essential of good distillery practice. For this reason great care must be exercised in the construction of the distillery so that no focal points for possible contamination will exist. This means all vessels, pumps, piping and fittings used in the process have smooth surfaces, free from projections or cavities. All joints must be made in gentle curves rather than at right angles. This requirement eliminates the possibility of the mash lodging in places which are hard to reach during cleaning.

For these reasons exaggerated knuckle joints should be used in construction of round vessels, sweeping bends should be employed in pipe lines instead of ordinary elbows, and plug valves and “streamline” fittings should be utilized. Where centrifugal pumps are used in mash transportation, they should be of the “dairy” type in which part of the housing is removable for cleaning purposes. Furthermore, all pumps, pipe lines and coolers must have small steam lines provided so that when the equipment is not in use it may be sterilized at atmospheric pressure.

The methods used in sterilizing mashing equipment differ slightly from plant to plant; however, the essential features are similar. Whenever operations cease for any considerable period of time, such as over the week-end, a dilute solution of caustic (sodium hydroxide) is placed in the cookers and heated to about 150°F. and allowed to stand until operations are to be resumed. The purpose of the caustic is to aid in the complete removal of any caramelized material in the cookers. Before starting up the caustic solution is again heated and then pumped through the entire system of mash lines and cookers and followed with hot water to remove the caustic. This cleans the system thoroughly. When mash lines, cookers, and converters are not in use, steam is supplied continually.

[Elizabeth Rhoades has a fantastic article on mashing in the Oxford Companion to Spirits and Cocktails that draws attention to pentosans which only get the most cursory mention here in a data table on splitting various materials including starches, proteins, and pentosans. It is also mentioned that the release of ferulic acid from the grain is important because yeast convert it into 4-vinyl guaiacol which is clove-like and contributes to rye’s spicy character. In a note below, we learn about acid resting steps in step mashing that release ferulic acid.

It is well worth checking out Liz Rhoades article on rye that tracks ferulic acid and offers some hints. An idea presented is thermally driven transformation of ferulic acid as an alternative to yeast driven transformation and may inform the benefits of the three chambered still which is known for thermal decomposition of the beer relative to a typical continuous beer still, especially after a less thermally intensive traditional step mash. The low volatility of 4-vinyl guaiacol is also noted and the three chambered still would maximize it because the upper chambers are essentially driven by flavored steam from below like a lagged retort pot still as opposed to nothing but clean direct injection steam. The lower chambers may have been exhausted of alcohol but they are still blowing 4-vinyl guaiacol upwards!]

[A valuable note on foaming, presumably during fermentation, turns up in the laboratory control chapter of FODP. Fat content of grain is most typically tied to the quality of distillers dried grains, but a higher fat content may also reduce foaming and may be a consideration when evaluating various grain types. It would be interesting to know if any particularly high fat content corns were added in small amounts to pre-prohibition rye mashes to harness any anti-foaming properties. It is known that during distillation additives like lard, turkey red oil, etc. have been historically added before modern anti-foam agents were invented. Silicon based anti-foams are under increased scrutiny for being toxic to effluent streams.]

[This fantastic article on Mash: Chemistry 101 by Matt Strickland gives a really helpful differentiation of alpha and beta amylase. It is not mentioned how optimizing for one enzyme class at a time in sequence could reduce viscosity, but it does help clarify how things function.]

[If you are interested in learning more about Pentosans related to foaming, I would read: Foam-Resilient Distillation Processes—Influence of Pentosan and Thermal Energy Input on Foam Accumulation in Rye Mash Distillation.]

[If you want to maximize the potential of endogenous enzymes, this is a great read with a thorough framing, but from a brewers perspective. I have been hoping for a term that may describe sequencing one amylase enzyme before the other to maximize viscosity reduction but I have not found one, however we find some related information worth quoting:

Beta-amylase attacks the ends of starch molecules and “snips” off the final two sugar residues, producing maltose. One noteworthy aspect to this is that starch molecules can be very long. If you want beta-amylase as your primary starch converter, then your mash will need a long rest in its optimal range. A 1–2 hour rest in the 140–145 °F (60–63 °C) range is, in fact, one way for brewers produce a highly-fermentable wort for drier beers.

Alpha-amylase is the second enzyme that is used for starch conversion. The optimal temperature range of alpha-amylase is around 155–162 °F (68–72 °C), although it is still active to a lesser degree at lower temperatures. Alpha-amylase attacks starch molecules at random points along their chains. It is bulky enough that it is not able to attack the starch molecules around branching points. A rest in the high end of the alpha range will result in a less fermentable wort, resulting in a sweeter, more full-bodied beer. In particular, a short (20 minute) rest at 158–162 °F (70–72 °C), in a relatively thick mash (around 1.0 qt./lb. or ~2 L/kg) will produce a very thick, full-bodied beer.

And then a note on water that may be relevant:

Alpha-amylase is less active and less stable in worts with low levels of calcium ions. This instability is increased in thin mashes and mashes in which the pH is above the recommended range.


[This wonderful youtube video describes a second stage of acid rest (104-122°F) in step mashing (before the protein rest which is runs right into) where a fairly low temperature rest is used to release acidity from the grain to drop pH naturally as opposed to adding acidity which is sometimes prohibited in beer production. This is probably much more significant to the nuance of direct consumption beers, but for the distiller, can release ferulic acid acid which is a precursor to clove aroma.]

[A group that is pushing the boundaries of maximizing the potential of less than ideal endogenous enzymes are people making gluten free beers where gluten containing malt cannot be added and they want to avoid exogenous enzymes.]

[A great reference is S.A. Wright’s chapter of The Alcohol Textbook 6th edition on pages 203/204. The author outlines multiple cooking options, but I’ll just quote 2 and 3. The first uses exogenous enzymes:

Low temperature cook, with or without malt

Rye, barley and wheat mashes may be produced using low temperature mashing for the production of American straight whiskies and blending distillates for American and Canadian blended whiskies. The grains are cooked as low as 85°C with or without a pre-liquification rest on the heat cycle. After the cook hold, temperature is reduced for conversion if malt is being used. High levels of wheat, rye or unmalted barley can add substantial viscosity to the mash and this can be addressed by adding one of the specialty enzymes xylanase, pentosanase or β-glucanase, either on the heat-up or the cool down of the mash. Users should refer to their enzyme supplier for the appropriate enzyme and usage instructions.

The third option seems more old school and embraces the pre-prohibition wisdom:

Whole grain infusion mash

Infusion mashing can also be used to describe a low temperature whole grain mashing process that is used on rye, wheat, malted barley and malted rye in the production of straight whiskies and various blending distillates for American and Canadian whiskies. Grains are slurried with water and malted grain(s) and backset is added in some cases. The mash is brought up to the gelatinisation temperature of the grains with protein rests along the way at temperatures to encourage the proteolytic activities of the malt to generate dipeptides and free amino acids for yeast nutrition and glucanase activity to reduce mash viscosity and help release bound starch. The low temperature of this mashing process conserves most of the amylolytic activities of the malt, which will remain active after cooling to fermentation temperature. The low heat exposure allows also for the survival of much of the bacterial flora of the grains which will also carry into the fermentation. The activities of this background level of bacteria during fermentation is generally considered beneficial to flavour development and will typically result in increased flavour complexity in the final spirits. The heating parameters of an infusion mash are often considered proprietary to the distiller, as they can have considerable impact on the profile of the end product.

Quite the paragraph! No doubt this means the old school is alive somewhere and the author has met a few people with opinions on it! When you compare the two options, the second with its naturalness somehow also invokes terroir to me with its tolerance of bacteria.


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