As part of the Experimental Archaeology Conference EAC12 hosted by EXARC this spring, I ran a handful of gruit experiments. Many gruit-beer experiments concern themselves with flavor and herbal components. They do not consider how or why the gruit substance may contribute to a longer shelf life, nor the reason its reputation as an essential element in brewing persisted for centuries even after hops came into common use. The consistent occurrence of grain in the surviving medieval tax records indicates that the grain aspect of the malt could be considerably more important than previously thought.
My experiments examine how the gruit substance affects fermentation and alcohol content, and therefore shelf life, leading to greater economic possibilities. In this blog post I will show you behind the scenes, so to speak, and share with you a bit more context and explanation than I was able to squeeze into my 5-minute video poster presentation. The experiments do not discuss gruit in the modern obsession of brewing with whatever herb one can get their hands on; to capture the essence of terroir, preferably in defiance of the hops establishment. While being much fun in its own right, it is not a very historic practice. My interest is in the medieval product itself: the substance of gruit and its herbal additives, and how this relates to the increased economics of the produced beer.
Contrary to what many modern publications would like us to believe, the historical sources are quite persistent that gruit is something more than just a collection of regionally unique herbs. A closer look at the etymology of the word gruit indicates an intimate connection with malt, in the form of coarsely ground grain. Even with variable medieval spelling, the different variants of the word are consistent with each other, and mean either the substance gruit, the beer brewed with it, coarsely ground grain, and the porridge made with such. Several Latin deeds use the words frumentum and polenta to describe the substance gruit, both words indicating a grain product. (Doorman 1955, 72; Ebbing 1994, 26-27; Kieft 1964, 165; Verberg 2018, 69)
If Low Country gruit indeed consisted of a concentrated malt porridge fortified with preserving botanicals and possibly yeast-rich chaff, then this would also explain several other Latin terms associated with the gruit product. When concentrated malt is added to the wort at the time of pitching, the boost of fermentable sugars would significantly enhance yeast fermentation. This would result in visible fermentation signs, giving the impression the gruit caused the “ferment” to happen. This effect resulted in the term levarentur for gruit, which is the Latin for leaven, or rising, and is also used for leavened or risen bread. As the concentrated paste caramelizes during the cooking down, adding this concentrate could darken the color of the wort as well, as suggested with the term pigmentum. The increase in fermentable sugars would raise the alcohol by volume, which combined with the preserving herbs and postponed spoilage just long enough for local commerce to be possible.
Two of the term definitions — gruit from the Low Countries, and grout from the British Isles — are connected to brewing. In the case of Low Country gruit, its connection with herbal ingredients is undisputed, while its connection with malted grain is questioned. In the case of British grout, a partially fermented cooked malt extract used to strengthen wort, interestingly, its connection with malted grain is undisputed – it is a known yeast-malt concentrate. It is not clear whether herbs played a role in medieval production, but they are not mentioned in early-modern grout descriptions. (Dodoaeus 1644, 813; Karkeek 1877, 196-97; Verberg 2018, 52)
If the substance of gruit indeed consisted of two parts – something produced with malt and heating equipment, and a combination of preservative botanicals – then it would stand to reason the malt portion is comparable to the malt product of British grout. And while there are no medieval recipes or process descriptions for medieval gruit, we are lucky with a couple post-period instructions for a similar product with a shared background.
I had located three publications which shared recipes on how to make grout. (Know of any others? Please share!) The 17th century publication quotes the 16th century source, and all three are about British grout. This is not unexpected, as by the 16th century, although in some areas the taxation is still active, the production and sale of the gruit substance had just about died out without a trace.
The first to publish a recipe for grout is the Dutch botanist Matthias l’Obel, also known as Lobelius, in his herbal Kruydtboeck oft beschrijvinghe van allerleye ghewassen, kruyderen, hesteren ende gheboomten First published in 1551, the edition that is freely available today, and from which I quote, is from 1581.
“Graut wordt aldus ghemaeckt. Neemt ses of acht ponden ghemalen Mouts / siende heet water xij. oft xv. pont / de welcke tsaemen gheroert en wel onder een ghemengt zijnde ses mael sdaeghs / en met cleedere en stroo zeer we ghedeckt zijnde soo langhe tsaemen in een schoon vat sal staen weycken tot dat soo dicke wordt als een syroop. Daer nae salt voorts metten viere opghesoden worden / alleneen zeer neerstich roerende op dat niet aen en berne / tot dat soo dicke als pap gheworden is.” Graut is made thus. Take six or eight pounds of ground malt / seething hot water 12 to 15 pounds / the which is stirred together and is well mixed six times a day / and with cloths and straw well covered, shall soak so long in a barrel until it becomes thick as syrup. After that shall it quickly be heated with fire/ only stir very well as that it does not burn / until it is as thick as porridge.L’Obel 1581
This recipe is reiterated by another Dutch herbalist, Rembert Dodoens (latinized as Rembertus Dodonaeus) in his herbal Herbarius oft Cruydt-Boeck. The 1554 edition titled the Cruijdeboeckonly lists botanical detail, which in the 1644 edition is updated and expanded upon to include product history as well as the occasional practical recipes.
“Graut of Naerbier wordt aldus ghemaeckt / seyde Lobel: Neemt sex of acht ponden gemalen Mouts / twaelf oft vijftien ponded siedende heet water: Roert dit tsamen wel onder een / zes mael daegs: Decket seer well met cleederen ende stroo: ende laetet tsamen soo lange in een schoon vat staen weycken tot dattet soo dick wort als eenen Stroop. Daer nae suldij dat voorts metten viere opsieden / alleen seer naerstich roerende / op dat niet aen een berne / to dattet soo dick als pap geworden is.” Graut or Naerbier is made thus / said Lobel: Take six or eight pounds of ground malt / twelve or fifteen pounds seething hot water: Mix this together well / six times a day: Cover it very well with cloths and straw: and let it soak together for so long in a clean barrel that is becomes as thick as a syrup. After that cook it up again with fire / only stir very well / as that it does not burn / until it becomes as thick as porridge.Dodonaeus 1644, page 813
A much later version, associated with the infamous White Ale, is published by Samuel Gray in The Operative Chemist (1828):
“Pale ale wort 25 gall, hops 2 handfuls, yeast 3lb, grouts 6 or 8lb. When the fermentation is at its height, bottle in strong stone half pints, well corked and wired; it effervesces when opened. The grouts here mentioned are made by infusing 6 or 8lb of malt in a gallon and a half of water, covering it warm by the fire side, stirring it often: when in full fermentation it is to be boiled down to a thick paste.”Gray 1828
The etymology of the British word grout is very similar to that for continental gruit, and points back to the shared Latin term grut. It is entirely possible British grout and Low Country gruit shared common ancestry, but evolved separately. But how likely it would be for the two products, used in a similar way, to deviate so much, so quickly, is debatable. It is more likely the two shared more than their names, their use as additive in brewing, their reputation of a potent ferment – they probably also shared their base ingredient: the grain. Dutch historian Irsigler came to a similar conclusion: “What is certain is that a porridge was prepared from the various basic ingredients, especially from bog myrtle, ground malt, laurel berries and laserwort, which was heated, and then dried again.” (Alberts 2017, 52; Dodoaeus 1644, 813; Ebbing 1994, 29-30; Hornsey 2003, 530; Irsigler 1973, 84; Verberg 2018, 58-59)
With this in mind, I choose to run a small experiment and brew three interpretations of gruit to test several variables:
- Could the gruit paste and gruit porridge, as instructed by the post-period recipes, adequately emulate the medieval gruit substance descriptions?
- Does the addition of this gruit paste or porridge significantly change the specific gravity (SG) of the wort and thus the resulting alcohol by volume (ABV)?
- Does gruit-porridge & syrup wort sour less quickly than the herbed, and/or plain wort?
For this I needed four samples:
- Sample 1: plain wort
- Sample 2: wort, plus the herbal & resin additive
- Sample 3: wort, plus a malt syrup with the herbal & resin additives
- Sample 4: wort, plus a grain-in malt porridge, with the herbal & resin additives
The wort was made by diluting a can of brewing malt extract to a SG of 1.05 (as advised for the brewing of standard 5% beer) and dividing the resulting wort over 4 one-gallon glass carboys.
I used a bread yeast as the more period-appropriate kveik starter was delayed in activation (our wood heated house might be too cold for its liking).
Producing the gruit substance
Taking inspiration from the above-mentioned recipes, in specific the one by Lobelius (1554), I devised the following process for the first trial gruit: the porridge.
Process: Add 8 lbs of ground malt and 1.5 gallon of boiling water to my copper brewing kettle. Cover well, stir often, for a day. The next day, place on wood fired stove and slowly cook down to a thick porridge. Stir well to prevent burning.
Result: This indeed produces a sticky, dry porridge. It caramelizes well but is difficult not to burn at the bottom. It is easy to incorporate the crushed dry herbs and heated resin.
As none of the recipes indicate whether the mash would be lautered (the liquid wort is filtered off the spent grains) and the wording is ambiguous (is it a syrup, or a porridge), I opted to make two versions, a grain-in and a filtered extract. The recipe for the porridge version did not generate much liquid, so for the syrup version I slightly tweaked the liquid volume to make sure there would be enough volume to concentrate (as the instructions do not suggest to sparge). The additives added later were adjusted accordingly.
Process: Add 6 lbs of ground malt (contained within a brew-bag) and 15 lbs (nearly 1.5 gallon) boiling water to the copper brewing kettle. Cover well, stir often, for a day. The next day, remove the brew-bag and thereby the grains (in lieu of a lauter tun). Place the kettle and the drained wort on the wood fired stove, and slowly cook this down to the consistency of syrup.
Result: This process produced a beautiful thick caramelized syrup. The evaporation did not require a lot of attention (unlike version one) and anyone with experience making jams and maple syrup will have no trouble recreating this. Be aware that hot syrup is more liquid than syrup at room temperature, without experience one could be tempted to overcook and burn.
The herbal additives
As suggested by the medieval gruithuis purchase accounts, I used the following herbs in the herbal mixture:
- Bog myrtle; leaves and catkins
- Laurel berries
- Caraway (substituted for the unavailable laserwort)
- Pine resin (colophon)
There are nearly no records available for the specific amounts of these herbs and spices in the gruit mixture. The one post-period recipe for Gruytbier uses very small amounts of herbs, and no malt (it does mention chaff; a gruit grain alternative, and something for another experiment).
“Om Gruyt, ende Gruytbier te maken. Neemt tegen eenen pot een koren bakelaer, ende alsoo veel aipoys, ende wat haveren doppen, ende twee saykens van gagel. Ende maeckt dit bier alleen van gherstenmoute, ende set dit dan met ghiste.” To make gruit and gruit beer. Take against one pot (half a gallon) a laurel berry, and also much resin, and some oat bran, and two seeds of bog myrtle. And make this beer only of barley malt, and set it with yeast.
The gruithuis accounts seem to indicate bog myrtle to be used most, and that laserwort was the most expensive ingredient. Modern science found that 2 grams per liter would inhibit lactobacillus souring (introduced 20 minutes before flame-out). Bog myrtle can have an overpowering flavor. The amount of herbs is adjusted according to the amount of malt used for the base gruit.
Gruit 1 (porridge) adjuncts: 30 grams of bog myrtle (20 gr leaves and 10 gr catkins), 30 gr of laurel berries and 5 gr of caraway seeds; as well as 42.5 gr (1.5 oz) of distilled pine resin. The herbs were crushed using a mortar and pestle.
Gruit 2 (paste) adjuncts: 22.5 gr of bog myrtle (15/7.5), 22.5 gr of laurel berries and 3.75 gr of caraway; 42.5 gr (1.5 oz) of distilled pine resin. The herbs were crushed using a mortar and pestle.
The four fermentation vessels are started as follows:
- Wort 1 (porridge) includes a half gallon of plain wort, fortified with 9 ounces of gruit porridge.
- Wort 2 (paste) includes a half gallon of plain wort, fortified with 4.25 ounces of gruit paste.
- Wort 3 (herbed) was fortified with 3.75 gr of bog myrtle (2.5/1.25), 3.75 gr of laurel berries, and 0.6 gr of caraway seeds; 5 gr (? oz) of distilled pine resin. The herbs were crushed using a mortar and pestle.
- Wort 4 (plain tester) is not fortified.
The carboys are capped with airlocks filled with star-san which will create bubbles to indicate active fermentation. They are then placed on a heating mat and wrapped with a blanket as the ideal fermentation temperature for bread yeast is 70-80 F (21-27 C).
At regular intervals, the specific gravity (SG) of the wort was tested. The addition of the gruit paste and porridge significantly raised the amounts of sugars in solution, raising the specific gravity and thus the alcohol by volume (ABV). The addition of extra sugars to a grain wort is also found in Farmhouse brewing, and is thought to have originated with the brewing with oats instead of barley. Oats do not saccharify as efficiently as barley and wheat, and to still make a strong beer, the Farmhouse brewers would add extra sugars. Oats are easier to grow, and in much of the Low Countries oats were the norm.
The table below indicates the starting or original gravity of the four different wort samples, as well as the final gravity reading at three weeks. The alcohol by volume is calculated as follows: (FG – OG) x 131.25 = ABV % The readings of the herbed and plain samples are identical, as expected, while the porridge levels are slightly higher than the paste. This is likely due to the spent grains not being sparged, or rinsed.
Original Gravity Final Gravity ABV %
Porridge 1.068 1.024 5.775%
Paste 1.062 1.026 4.725%
Herbed 1.052 1.020 4.2%
Plain 1.052 1.020 4.2%
The readings of this proof-of-concept experiment indicates that, yes, adding gruit paste makes for a stronger beer. This supports the theory that the gruit substance positively affects fermentation including alcohol content and thus shelf life, leading to greater economic possibilities.
Question: If the shelf life of the brew is extended, either through raising the ABV % or by adding preservative herbs, can this be tasted in the resulting brew? How fast do the different samples sour?
- Day 1: Pitched the yeast.
- Day 6: all samples are effervescent, and sweet.
- Day 12: The plain sample went sour (badly).
- Day 16: The herbed sample is going (nicely) sour.
- Day 20: The two gruit paste/resinated samples are still going strong, but unclear if this is due to the increased ABV or the potent resin.
Question: Can chaff (grain hulls) function as a source of spontaneous fermentation?
My experiment was not able to answer this specific question at this time as the local mill used to source fresh chaff in the past was closed to walk-ins due to the pandemic. But: the significant difference in the ABV % between the porridge (which includes the naturally yeasty chaff) and syrup might indicate there is validity to this: instead of providing active yeast, perhaps the chaff provides yeast nutrients and promotes vigorous fermentation. Happy yeast results in a quicker and potentially higher sugar to alcohol conversion. English grout uses dead yeast for a similar purpose.
Unanticipated Question: Does resin alone have a noticeable preservative effect, does the manner how it is added to the gruit paste matter?
The gruit syrup had a slightly higher amount of resin than the porridge due to oversight (did not account for the 2lbs difference between the two). The syrup brew stopped showing signs of active fermentation (bubbles) within a few days, unlike the other two, and it also tasted much more resiny (an unpleasant, antiseptic, mouth numbing taste). The heated liquid resin was poured into all three samples, but unlike my previous brewing with resin experiences where it was added to room temperature wort, it now was added to hot porridge and syrup as well. Presumably, the resin dissolved much more completely, dispersed much more finely, which significantly enhanced its preservative effect, as well as its unusual flavor. The resin flavor, while initially very sharp, did mellow out over time (now, two months later, it still has not soured and while it does not drink well, it does work great as a cooking beer).
The addition of herbs to plain wort somewhat slowed down the souring process. The addition of grain paste to raise the SG slowed down souring even more, and the use of resin boosts this protection further. Concentrating gruit porridge takes more effort to prevent burning than concentrating into syrup, but unexpectedly, the benefits of a higher OG (no wort lost by removing the spent grains) and possible yeast nutrients could make up for this inconvenience. The addition of resin might be more important in connection to the preservative function of gruit than previously assumed.
Food Drinks for thought…
That the ABV percentage would be higher after adding concentrated malt (gruit paste) was assumed, but the difference is more significant than initially expected. Porridge gruit could be a viable option: syrup seemed to be the obvious choice but the experiment seems to indicate porridge to be more efficient. The difference in application between adding hot resin to cold substrate as opposed to adding hot resin to hot substrate is significant. The unexpected effect seems reminiscent of my wax comb mead experiments, where the hot wax dispersed into the wort but did not re-solidify when cooled, and further investigation is warranted.
Poster presentation at the Experimental Archaeology Conference #EAC12, Wednesday March 31st, Session 12. After the presentations follows a one-hour live session with Questions & Answers. Please Join us.
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