Brewing Lambic

← An Overview of Lambic

Introduction

Lambic is brewed seasonally, with the brewing season extending roughly from October to May. The exact dates for beginning and ending the brewing season are determined by the nighttime temperature and the brewer’s preferences. Because traditional lambic is cooled overnight in a shallow pan called a coolship by exposure to outside air, cold temperatures are necessary to properly cool the wort. Additionally, there may either be undesirable bacteria or an undesirable microbe balance in the air in warmer months which can negatively influence the fermentation and the developing flavor profile of the lambic.

The hot side of traditional lambic production involves a time and labor-intensive mashing process known as turbid mashing, where cloudy or turbid wort is removed from the mash before it is allowed to completely convert. This turbid wort contributes complex carbohydrates and proteins to lambic wort which can feed a diverse community of yeast and bacteria during the long lambic fermentation process. Lambic then undergoes a long boil where hops which typically have been aged at least a couple of years are added. Finally the wort is transferred to the coolship for overnight cooling.

2014 Perle hops aging at Cantillon, May 2016.

Raw Ingredients

The Royal Decrees of May 20, 1965 and March 31, 1993 required that lambic brewers use at least 30% wheat. Today's modern lambic is brewed using a grain bill of roughly 30-40% raw (ungerminated) wheat and 60-70% malted barley (2-row or a combination of 2-row and 6-row). Recipes from the 1800s actually called for even more unmalted wheat. In most cases, both the wheat and the barley are coming from Belgian or German farms.

Aged hops also play an important role in lambic. Hops are necessary to regulate the growth of bacteria; however higher doses of fresh hops could add an unwanted level of bitterness. This is why hops over a year old are used; they have lost the majority of their bittering properties but not their bacteriostatic properties. Traditionally, hops containing low amounts of alpha acids are aged for anywhere between a year and three years; although some bales of hops wind up aging much longer. The hops are typically stored in an environment where they are susceptible to oxygen and drastic temperature changes, such as in sacks in an attic, rather than the vacuum sealed and cold storage common for beers using un-aged hops.

Equipment

Hot side equipment

Cantillon's mash tun

While some specialized equipment is used in the ‘hot side’ of lambic production, much of the equipment used in modern lambic breweries resembles the sort of equipment you would see in contemporaneous Belgian non-lambic breweries. The typical hot side equipment found in lambic breweries includes a mash tun with internal rakes, one or two boiling kettles, and a coolship. Additional necessary brewing equipment which may be more or less visible, depending on the brewery, includes a grain mill, access to hot water through either a dedicated vessel (termed a hot liquor tank) or through on-demand hot water, and pump(s) which are either belt-driven (e.g. Cantillon) or directly electrically powered (e.g. 3 Fonteinen). Significant variability exists between different producers in the specifics of this equipment based on size and when the brewery was built, but their function and general characteristics are basically the same.

The mash tuns used in lambic production deserve specific discussion before dealing with brewing process. A mash tun is the vessel that holds the mixture of grain and water (the mash) as enzymes in the grain are active to convert components of the grain into fermentable sugars and accessible nutrients for yeast and bacteria. Mash tuns have a false bottom made of a perforated or slotted screen which allows liquid to pass below while retaining the grain. Historically wooden baskets (called stuykmanden in Flemish) were also used to extract liquid from the mash. These baskets were pressed into the mash and turbid wort was withdrawn and transfered to a boil kettle. Mash tuns have internal rakes which aid in mixing the mash as well as draining the sweet wort after the mash is complete. Along with the rakes, some lambic breweries (e.g. Timmermans) have perforated copper disks called extractors inside the tun which were used to help withdraw liquid from the mash..

Barrels

Barrel cleaning at De Troch

While some larger producers are using stainless steel tanks, lambic is traditionally fermented and aged in wooden barrels and foeders. Lambic brewers and blenders prefer used barrels, which are often coming from red wine production, for fermenting and aging lambic. These barrels are preferred because most of the oak character has already been extracted from the barrel, and less character from the wood will come through in the final lambic. Barrels vary widely in size, including sizes such as 267 liter Tonnes, 550-650 liter Pipes, and 3,000 to 120,000+ liter Foedres. Each brewer has their preference for their ideal barrel size. These barrels are typically made from oak or chestnut.

Each individual barrel can have its own progression, even among well used barrels and different barrels from the brewing day, and some lambic brewers and blenders are experimenting with more distinctive barrels where the influence of the previous contents of the barrel are desired. Increasingly, lambic producers are releasing beers highlighting the unique role that different barrels or foeders can have. This includes sourcing specific barrels or foeders for their characteristics as noted above, as well as bottling the first lambics from recently-received used barrels as separate releases, and releases highlighting a single foeder or selection of older barrels. Some examples of this are:

Barrels used for spirits

• Boon Vat 110 Monoblend (Cognac)
• Boon/Mikkeler Oude Geuze (Calvados Aged) (Calvados)
• Cantillon 50N 4E (Cognac, Armagnac)
• Cantillon Chouke (Armagnac)

Barrels used for oxidative wines

• 3 Fonteinen Zenne Y Frontera (Sherry)
• Cantillon La Vie est Belge (Vin Jaune)
• Cantillon Brabantiae (Port)

First use(s) of wine barrels

• Cantillon Zwanze 2018 (Amarone, Chianti, Sangiovese)
• Oud Beersel Vandervelden 135 (Brunello di Montalcino)
• Oud Beersel Vandervelden 137 (Brunello di Montalcino)

Old barrels

• Boon Vat 79 Monoblend (from a foeder built in 1883), along with many of the other monoblend series
• Oud Beersel Oude Geuze Barrel Selection Oude Pijpen

Barrel cleaning is important for lambic production; however, the exact methods used vary among individual brewers and blenders. Some basic steps are fairly universal. First, any sediment is removed from the barrels by spraying with hot water and, in some cases, scrubbing. Some brewers (such as Cantillon) scrape barrels clean by putting sharpened chains in the barrels and spinning them. The barrels are then washed extensively with with very hot water and/or steamed to sanitize and prepare them for use. If they are to be stored empty rather than being reused promptly, the barrels are allowed to dry and sulfur is burned in them to preserve their sanitation. Even with this extensive cleaning, the barrels still carry microbes and contribute to the fermentation of subsequent batches of lambic and only superficial cleaning of barrels can alter the progression of lambic fermentation.

Turbid mashing

Introduction and brief history

Lambic production employs a time and labor-intensive mashing process known as turbid mashing. Belgian legal structure in the 1800s favored mashing procedures like turbid mashing as they allowed for a lower water to grain ratio to be used while more effectively extracting carbohydrates from the grain. Turbid mashing involves the removal of mash runnings before the mash is completed. These turbid runnings have not been fully converted in the mash and therefore they contribute complex carbohydrates and proteins to lambic wort which can feed a diverse community of yeast and bacteria during the long lambic fermentation process.

Although turbid mashing may be beneficial to the specific conditions of lambic fermentation, and lambic is one of the last remaining beers to use this process commercially, the method and similar mashing procedures were used historically for a variety of different beers in Belgium and northern France (e.g. bière de garde). Among Belgian beers using turbid mashing were low ABV beers which were not intended for long aging. In comparison to the single infusion system of mashing favored in England, or even multiple step infusion mashes without the removal of turbid wort, Belgian brewers around 1900 felt that turbid mashing resulted in beers with a fuller body and richer flavor development.

Process

The lambic grist of malted barley and raw wheat must be milled before they can be used for brewing. This may occur the day before brewing or on the morning of the brew. The brewing process begins when the milled grains are transferred into the mash tun and mixed with water. This mixture, termed the mash, is carried through multiple rests by infusion of hot water to reach different resting temperatures. The temperature rests of the mash are controlled to hit ranges where different enzymes within the malted barley are active on components in the grain, such as converting starches in the grain to fermentable sugars and breaking down proteins.

Turbid mashing begins with very a very thick (low water to grain ratio) and cool temperature rest compared to standard mashing. This helps the mash avoid becoming ‘set’ or solidified due to low water to grain ratio and high amount of ungelatinized raw grain traditionally used in lambic breweries. Subsequent rests are achieved by the addition of near boiling water (called infusions) to raise the temperature of the mixture. The exact number of steps and target temperatures of the steps varies among different brewers, but typical steps include a beta glucan rest, a protein rest, multiple saccharification rests and a mash out. These rests are discussed further in the example mash profile below.

Draining turbid wort from the mash at Cantillon

Turbid mashing derives its name from the cloudy or turbid wort which is drawn off at specific points during mashing process. This cloudy wort contains starches and proteins which have not been broken down by the enzymes in the mash into fermentable sugars, shorter peptides and amino acids. Turbid wort is transferred to a boiling kettle and heated to near boiling temperatures, denaturing the enzymes present in the liquid and preventing further conversion of starches or proteins. In most lambic breweries this is accomplished in a second boil kettle, but in some more modern breweries (e.g. 3 Fonteinen) where only one kettle is present, the turbid runnings are heated in the single boil kettle. Due to the starch and protein rich nature of this wort, care must be taken with this wort to avoid scorching during heating. In some breweries, kettles for turbid runnings have chains or propellers (e.g. Cantillon) to ensure the turbid wort is mixed and does not scorch. In some breweries, especially those using older equipment, the removal or turbid runnings is also necessary to provide sufficient space for additional infusions of water to reach the remaining steps of the mash.

Once the mash is complete the sweet wort is separated from the grain by draining through the false bottom. As with non-lambic breweries, the wort is recirculated back into the mash tun first to aid in clarification before collection of wort in the boiling kettle(s). The turbid runnings are then added back to the mash. In the case of breweries with two boil kettles this is done after the mash is drained for the first time. At breweries with only one boiling kettle the turbid wort is added back before recirculation and draining of the mash. After the mash and turbid runnings have been drained, the grain is rinsed with near-boiling water in a process called sparging. Sparging temperatures in lambic breweries are much higher than in conventional breweries. The sparging process ends at the discretion of the brewer, generally when the target pre-boil volume is reached or when the grains have almost no soluble material left to contribute to additional sparges. Wort collected from draining the mash, the turbid runnings, and from the sparging is combined into one or two boiling kettles (depending on the brewery) and the wort is boiled.

An example of a turbid mash schedule, adapted from Guinard (1990), Sparrow (2005) and Cantillon’s current process is as follows:

• Mix water and grain to reach a rest temperature of 45C/113F for 10 minutes. At this temperature rest enzymes are active to break down beta glucans in the raw wheat, helping the mash to be more fluid at later steps.
• Add near boiling water to reach a rest temperature of 58C/136F (protein rest). The enzymes active in this temperature range break down proteins. Rest for 5 minutes.

Cantillon's boil kettle with mixer to prevent scorching

• Extract a portion of turbid liquid from the mash and transfer to a kettle for heating to 80C/176F.
• Add near boiling water to reach a rest temperature of 65C/149F (saccharification step 1). The enzymes active at this step convert starches in the grain into fermentable sugars. There are two main enzymes active in the saccharification temperature range. At cooler temperatures, such as in this rest, the balance between these two enzymes favors the production of simpler sugars. This temperature is held for a rest of 30 minutes.
• Extract a portion of turbid liquid from the mash and combine with the previous turbid liquid. The mixture is heated to 80C/176F.
• Add near boiling water to reach a rest temperature of 72C/162F and rest for 20 minutes. This temperature also falls into the range of saccharification enzymes. The warmer temperatures of this rest favor the production of intermediate chain length saccharides which may be less fermentable to normal brewer’s yeast but may be accessible to certain bacteria and additional yeast found in lambic fermentations.
• Drain the wort into a separate kettle for boiling. This wort is heated toward a boil once enough wort is present in the boil kettle to allow heating without scorching. A boil may be reached before the final runnings are collected, or it may begin shortly after the final runnings are collected.
• Transfer the hot turbid wort back to mash and mix with the grain. This raises the temperature to near 78C/172 F. The mash is allowed to rest for roughly 20 minutes at this temperature. In the case of a brewery with only one boiling vessel, this step is done before draining the mash into the boiling kettle. In that case it is necessary to ensure that sufficient space remains in the mash tun for the turbid wort to be added back. This is then drained off into the boil kettle.
• Begin sparging (rinsing) the grain with water at 85C/185F. The wort collected from sparging is transferred to the boil kettle.

Boiling

Historically boiling for lambic could have lasted 12 or more hours, but modern practices generally lasts between about 2 hours and 5 hours. Boiling serves a few purposes, including:

• Sterilization of the wort

The split-level, 4 compartment coolship at 3 Fonteinen

• Extraction of hop antibacterial compounds.
• Reduction of hop aromatics. The aromatic compounds of hops are volatile and are driven off during the boil.
• Caramelization of the wort via to Maillard reactions.
• Reduction of volume. The extensive sparging (rinsing of the grain) during mashing dilutes the sugar content of the pre-boiled wort, and the extended lambic boil helps to concentrate the sugar content.

Hopping

Boiling is also when hops are added. The brewer will make a hop addition as the kettles are being filled, before the wort actually begins to boil. Other than being aged, there is a lot of room for variability in lambic hopping among producers. Hops grown in Belgium, the Czech Republic, Germany, the UK and North America are used (note that many modern Belgian grown hops are varieties which originated in the UK). It is important to use hops with low alpha acid content as brewers are not looking for bitterness or acid contents; only the antimicrobial properties contained within the hop.

Cooling and Inoculation

After boiling is complete, the wort is sent through a filter (often a simple metal screen) to clear the wort of major hop and trub debris. This slow process will eventually drain the wort into a vessel called a koelschip (coolship). Coolships often reside in the brewery's highest most point next to slatted windows so that the cool night air can deposit hosts of microorganisms that will ferment out the wort into lambic. This process can only happen during the cooler months of the year due to the fact that molds have a difficult time surviving the cold temperatures. It will take the wort a period of about 10 hours to cool to the desired temperature at which point it will be transferred to barrels.

Fermentation

Fermenting lambic with overflow tubes at Gueuzerie Tilquin, winter 13-14

Initial Fermentation

The wort is transferred via hose into the barrels through the top bung hole. Barrels are completely filled and loosely capped with a silicon or wooden cork. In some cases a tubing system will serve as an overflow into buckets for when initial fermentation begins; making it easier to clean up after the barrels. Fermentation will typically occur within a few days, but can take up to a couple of weeks to begin. Factors that can affect when fermentation begins include the temperatures during inoculation or the temperatures during those first few days in the barrel. Organisms work more quickly at higher temperatures.

Continued fermentation and aging

Lambic will develop and rest in the barrels for between a year and three years in most cases. Some experiments have led to lambic resting for upwards of five years though. As lambic ages in the barrel, it matures. It takes on a more complex profile as different yeasts and bacterias interact, die off, rearrange esters and fermentation byproducts, etc. The lambic's sugar content is decreased over time and it becomes drier. It will also take on more of the barrels character due to longer exposure time and will oxidize.

Topping Up/Maintenance

Most barrels are topped up only once after initial fermentation has completed and there is a significant airspace between the lambic and the bung. After most CO2 production has been completed, the barrels are hard-bunged and left to rest indefinitely.

Fruiting

Fruit Selection/Preparation

The most commonly used fruits in lambic production are cherries (Kriek) and raspberry (Framboise, Framboos). Many other fruits have been experimented with in the beers discussed on this site. Examples include plums, blueberries, gooseberries, apricots, currant, strawberries, apple, banana, and a variety of wine grapes. Traditionally whole fresh fruit was steeped in lambic of minimum one year but many brewers use frozen fruit or fruit extracts/juices in their modern processes.

Duration

Traditionally, fruit and lambic is racked into barrels. Today however, some brewers use stainless tanks for blending lambic and fruit. Whether in a barrel or a stainless tank, the fruit and lambic are usually stored together for between four and eight weeks. Most fruits are added whole without being crushed or pitted. Once fermentation is completed, the now fruited lambic is transferred to a bottling tank through a filter. The filter could be cellulose or any other type of filtering material.

Fruit ratios vary, but generally run between 200 and 400 grams of fruit per liter of barrel space (as opposed to 200 to 400 grams of fruit per liter of beer). For example, saying "300 g/l" in a 650 liter pipe, means that there is ~195kg of fruit added to the barrel.

Blending

Fruit Lambics

Fruit lambics are typically not blended with other fruit beers. In some events, if the lambic shows too much sign of fruit (over-fruiting), the brewer will blend in some unfruited lambic to mellow the flavor.

Gueuze

Gueuze is loosely defined as a blend of 1, 2, and 3 year old lambics. This ratio is very dependent on the blender's intentions, what barrels are available to choose from, and what those barrels provide in terms of flavor profile. Recently, more blenders have been experimenting with adding 4+ year old lambic to blends.

Generally speaking (and never a steadfast rule): 3 year lambic will be softer and more mellow, providing a nice base. This is used in lower proportions. A 2 year lambic will provide the most character and interesting nuances in a blend. This is used in slightly higher amounts. A 1 year lambic will provide fresh, active yeasts to further develop the blend once it is bottled, along with more fermentable sugars for bottle fermentation. This is used in the highest proportion. Again, this is not always the case. Sometimes a brewer may choose to use any age lambic in a much higher proportion than outlined here. The process is guided by tasting and smelling barrels.

The specific gravity of the final blend must be high enough to ensure that bottle refermentation occurs.

Pasteurization

In 1865 Louis Pasteur "discovered that heating beer and wine just enough to kill most of the bacteria that caused spoilage prevented these beverages from turning sour. This was achieved by eliminating pathogenic microbes and lowering microbial numbers to prolong the quality of the beverage."

Some lambic brewers choose to pasteurize their product prior to the completion of secondary fermentation. This allows for a sweeter product, retaining a lambic or gueuzes residual sugars and, in the case of a fruited lambic, the sweet fruit flavors. It also eliminates refermentation in the bottle and minimizes other changes to the beer, allowing industrial lambic producers to ensure a more consistent product that does not continue to develop.

Bottling

Depending on the sugar content (gravity) of the final blend/lambic, sucrose sugar may be added in small amounts to provide food for yeasts to feed upon in order to aid in the creation of carbon dioxide within the bottle. This is adjusted according to the level of desired carbonation.

During the bottling process, lambic is sent from the stainless steel bottling tank, typically fed by gravity. Bottling machines, technologies, and techniques vary widely from brewery to brewery. Unlike when other beer styles are bottled, lambic bottles are often not flushed with CO2 prior to bottling.

Lambic bottles are thick walled, reinforced and, Champagne-style. The bottles are generally green or brown in color. During bottling, bottles are filled to the arch of the neck and topped with either a wine or 'mushroom' styled cork. In the case of a wine cork, a metal crown cap is applied to help maintain the carbonation and to prevent the cork from popping out during the production of CO2 within the bottle.

Bottles are left unlabeled until time for sale. They are left for a minimum of three months, though most blenders prefer to age their bottles for minimum six months before sale, especially in the case of geuze. This will allow bottle conditioning to occur, and allow the beer to work through phases of viscosity that may occur (Pediococcus byproducts known as 'ropiness').

References

← An Overview of Lambic