Lambic Brewing

Lambic is a traditional Belgian style of sour beer. After boiling the wort —made from pale malt and 30–40% unmalted wheat — the brewers expose it to airborne yeast and bacteria overnight. Then it is pumped to casks (where it is likely inoculated with more microorganisms). The fermentation by many different wild yeasts and bacteria produce a beer that is not only sour, but shows a variety of other characters, including a horse blanket or barnyard character that varies from subtle to pronounced.

There is no detectable hop contribution in a lambic. Sorry, it just isn’t a style for hop heads. Lambics range from nearly flat to effervescent. The beer may be cloudy or clear, the head may be strong to weak to non-existent. The color may be straw or pale gold, but I have also noticed some subtle hints of pink in some well-aged examples of straight lambic and gueuze. Fruit is added to some lambics to make fruit lambics, including kriek (cherry) and framboise (raspberry).

I have won several medals for my homebrewed lambic, so people often ask me about how I brew them. Although the traditional wort production techniques involve some unusual aspects — including using unmalted wheat in the mash and large doses of aged hops in the boil — the distinct character of lambic comes mostly from what occurs after the wort has been boiled.

The Lambic Family

The starting point for the family is the traditional (straight or unblended) lambic — a complex, dry, sour, yellow or deep gold colored beer. A gueuze is a blend of young and old lambic, typically containing from 15% to 70% old lambic in the blend. Some, however, like the Boon Mariage Parfait, are much closer to 100% old lambic.

Various fruits are used to flavor some lambic styles. The original fruit lambic was probably the kriek (Flemish for cherry). A kriek lambic is traditionally made using the tart Shaarbeek cherries that are only grown in Belgium in a region to the northeast of Brussels. Now days the Shaarbeek cheery is fairly hard to find and expensive so some brewers also use the Moreno or Northern cherry as part of the fruit addition. Tradition calls for the use of whole cherries including pits. The belief is the pits add to the flavor depth. The framboise (French for raspberry), which apparently originated in the 20th century, is made from red raspberries.

The lambic family is the only one still in commercial production that uses spontaneous fermentation — the brewer does not pitch a cultured yeast strain into the wort. A spontaneous fermentation that produces the flavor characteristics of a lambic is said to only work in a small area around Brussels, where the proper microbiota exists in the air between October and May. Some writers claim the microbiota is in the brewery’s equipment rather than the air. Major organisms involved in the spontaneous fermentation include the traditional brewer’s yeast Saccharomyces cerevesiae, the “wild” yeasts Brettanomyces lambicus, Brettanomyces bruxellinsis and Kloeckera apiculata, the bacteria Pediococcus and Lactobacillus and various enteric bacteria such as Enterobacter, Klebsiella, and Hafnia. The Brettanomyces strains produce the signature horse blanket, leathery or barn-like aroma. Pediococcus and Lactobacillus produce lactic acid.

The acidity of a lambic can range from mild in commercial examples such as Lindemans or Timmermans to extremely sharp as in examples such as Hanssens or Cantillon. I assume that there is also a significant impact on the acidity from the brewer’s barrels, since they are impregnated with the cultures from previous batches. In young lambic, the sourness is mostly from lactic and acetic acids. As the age of the lambic increases the acidity becomes more complex and balanced.

In many ways a lambic is a varietal product — even if the brewer was able to exactly control the brewing session and get exactly equivalent ingredients, each batch will vary due to the variation in the environment within the brewery over the several years between when the wort leaves the kettle and when the bottles leave the brewery. Most lambic breweries do not heat or cool the bulk of the brewery. The changes in the temperature and the humidity will change the growth rates of the various organisms that contribute to the flavors. Temperatures in the brewery can range from the mid 30s Fahrenheit (~2 °C) to the upper 70s (~25 °C). In addition, the atmosphere contains varying amounts of the various relevant organisms on different brewing days.

Finally, since the barrels are not coated on the inside, there can be barrel-to-barrel variation due to the organisms that have permeated the barrels. When it comes time to bottle, the commercial lambic brewer blends the product from various barrels and batches to achieve the desired character. The palate of the brewer or blender is really what determines the “house” character of a lambic brewery.

Contrary to what you may read in many articles, lambic is not fermented in large, open-air fermenters. After boiling, the wort is pumped into the traditional shallow coolship that is usually in the top floor or attic of the brewery. The wort typically stays in the coolship overnight where there is a limited exposure to the atmosphere. Within 24 hours, the wort is typically transferred to wooden (continental oak or chestnut) barrels.

Advanced Planning Details

Brewing a lambic does take a little advanced planning as lambic is the only style that needs well-aged hops. There should be no hop aroma, flavor or bitterness in a lambic, but you do need the hops for their preservative properties. You want old hops that have aged beyond the “cheesy” state. Since pellets don’t age as rapidly, you should plan on using one to three year old whole hops. I store my hops for lambics in paper bags in the attic of the uninsulated garage. On sunny summer days it gets well over 120 °F (49 °C) in the attic, so the hops age rapidly.

You also need to acquire the proper brewing yeasts and other organisms. You can and should buy pure cultures of the main lambic cultures, including a Brettanomyces strain, Lactobacillus delbrükii, and probably Pediococcus damnosus. As additional research into the style, and as a source of some of the other microbiota found in a lambic, it will be necessary to drink some commercial examples of the style. Yes, it is hard work but it is research that must be repeated over and over again. I keep a starter that I add the dregs of the bottle to after pouring the beer into a glass. Beware that some of the less traditional examples seem to be pasteurized and therefore have nothing left to culture. You need to use a little care to avoid contaminating the dregs. I wipe the neck down with vodka before opening and then flame the neck with a small butane lighter after pouring the beer into the glass. The starter will probably develop a pellicle (skin) from the Brettanomyces and Pediococcus. If you see green floating mats, however, you have probably collected some undesirable mold. I also save the dregs from a batch when I bottle it and use those dregs in the next batch.

Fermentation Peculiarities

Traditional lambic is brewed in wood (continental oak or chestnut) barrels. Wood is somewhat porous and will allow a slow penetration of oxygen into the fermenting beer. I use the plastic bucket fermenters available in homebrew supply stores. Like the wood barrels, most plastic is also slightly porous to oxygen. I have taken to placing a small, approximately 1 by 3 by 6 inch, piece of American oak in barrel to become a home for the microorganisms. Initially, the oak pieces were soaked in water treated with sulfite (1 Campden tablet per gallon) for a few months, soaked until no color or flavor was extracted from the wood. The wood is rinsed in hot water between batches, but is not sanitized since that would evict all the microorganisms.

In Belgium, the barrels and even the bottles in aging are subjected to some temperature variations with the seasonal changes though the changes are probably gradual due to the large size of the barrels and the large numbers of bottles stacked in the brewery. Many of the best examples of the styles are aged for extended periods in the bottles. The wall of bottles on their side aging is impressive to see.

While the beer is in the fermenter, the pellicle provides some protection from oxygen. There are indications that barrels stored near vibrating machinery can end up more vinegary due to the vibration breaking the pellicle allowing more activity by acetic acid bacteria.

Brewing Specifics

You can brew a lambic with an all-grain process or with extract, but I take the easy approach — I brew extract versions. (For all the details on a traditional lambic mash, see Jean-Xavier Guinard’s book, “Lambic,” 1990, Brewers Publications).


My fermenters are normally in the basement that ranges from the upper 50s in the coldest part of winter to the upper 70s in late summer. The beer is never transferred or racked until it is time to bottle. In commercial lambic breweries, the beer might be coarse filtered on the way to the bottling line. For a homebrewer, a racking a day or so prior to bottling should be sufficient to remove most of the sediment. Priming can be with the typical corn sugar dose. However, it is a good idea to prime your lambic with the addition of a package of dried yeast just to improve the likelihood of getting some carbonation in the bottle. Since the pH is out of the norm for brewers yeast there is always a chance that the beer will never carbonate. I have had some batches carbonate with no problem and other batches that haven’t carbonated after several years.

If the lambic is to become a fruit lambic, the fruit will go in sometime around one to two years after brewing and the beer will sit on the fruit from three months to a year or more. If trying a kriek, a few months on the fruit should be sufficient. Some people claim the lambic will pick up too much bitterness from the pits if left in contact with them more than a few months. Other authors claim that kriek is left on the cherries and pits until the pits dissolve. In Belgium, after a beer sits on the cherries for a few months, it will be racked off the pulp and pits and a second batch will be racked onto the remaining fruit.

Of the fruit lambics, the framboise is the easiest for US homebrewers to approximate. Raspberries in the US are very similar to those used in Belgian lambics.

The cherries we are able to obtain in the United States don’t really do justice to the kriek style. If you want to try making a kriek, tradition calls for a kilogram or more of whole cherries per 5 L (~1.6 lbs./gallon) of lambic. Given the time required to produce a lambic, I would avoid the bottled fruit flavors sold in most of the homebrew shops.

For a batch of framboise, I typically use three cans (just over nine pounds) of Oregon Fruit Product’s Raspberry Puree. Since the puree is seedless, Oregon claims you can use 10 percent less puree than whole fruit. So, the three cans are equivalent to just over ten pounds of fresh raspberries. My most recent framboise used 20 pounds of frozen raspberries. I think the presence of the seeds in the frozen raspberries may also help provide some of the astringency noted in some of the classic commercial framboise examples.

I have just started a couple batches of fruit lambic using fresh wine grape juice, but at this point I have not determined the proper amount of juice for the best results. I have also tried blending several different (young and older) batches of lambics to produce a true gueuze. It is interesting to see how the flavors and aromas meld. Blending is an area of experimentation that could last a lifetime.

There are other opinions on how to produce a homebrewed lambic. All I have provided is a technique that seems to produce a decent homebrewed lambic for me. My process isn’t quite the same as the brewers at Cantillon, De Cam or Boon use. There is no one tried and proven correct way to produce a homebrewed lambic-style beer. Remember the commercial examples have a pretty broad range. Please feel free to experiment and share your results with other lambic homebrewers.


Piatz’s Basic Lambic
(5 gallons/19 L, extract only)

OG = 1.056 FG = 1.016 or lower
IBU = 0 SRM = 3 ABV = up to 5.2%


  • 3.0 lbs. (1.4 kg) light dried malt extract
  • 3.0 lbs. (1.4 kg) wheat dried malt extract
  • 0.25 lbs. (0.11 kg) malto-dextrin powder
  • 3 oz. (85 g) well-aged hops
  • mix of brewers yeast, “wild” yeasts and bacteria
  • (Wyeast 3278 (Lambic Blend) or mixture of commercial cultures and microbes cultured from commercial lambics)

Step by Step

The malto-dextrin is to be sure there are a few complex sugars left for the extra organisms to eat after the brewers yeast gets finished with its work. I use the dried extract since lambic is a very light colored beer and most liquid extracts seem to be too dark for the style. The wheat extract is a poor man’s approximation of the unmalted wheat used in the commercial lambic breweries. I don’t know of an extract equivalent of unmalted wheat.

The water is brought to a boil and the extract and malto-dextrin are added. After re-establishing the boil, the hops are added and the boil is held for 90 to 120 minutes. I don’t bother with Irish moss in a lambic, but you can use it if you feel the need. I run the hot wort directly from the kettle to the plastic bucket without chilling and will leave the wort in the bucket for a day or so with the lid partially open to the kitchen air, which is typically full of enteric bacteria. This exposure will allow the enteric bacteria present in the air to add their components to the beer. After the exposure to the air, I place the lid on the bucket and wait a few days before I pitch a normal brewers yeast. The variety doesn’t matter very much; I either use yeast from a prior “normal” beer or a packet of dried yeast. By this time the beer is starting to get a little “funky” and the surface may look a little oily. At this point I also add the treated piece of oak back into the bucket — do not run the hot wort onto it or you will be sanitizing it. The brewers yeast will rapidly change the pH and generate ethanol, both of which will help kill off the enteric bacteria but their byproducts will still be there. After a few weeks I add the other organisms, the Brettanomyces, Pediococcus, Lactobacillus and the dregs from commercial lambics and prior batches of homebrewed lambic.

Issue: October 2004