Saturday, 1 October 2016

Ester synthesis during brewery fermentation

Of late I've been reading Brewing Yeast Fermentation Performace by Katherine Smart*. It's full of fascinating facts and I found it a surprisingly easy read. This may have been helped by skipping the bits where it got into too much detail about genetics. Even I have my limits.

On chapter I particularly enjoyed was Control of Ester Synthesis During Brewery Fermenation. Just look at the start to the introduction:
"The synthesis of volatile aliphatic esters by yeast is of major industrial interest because the presence of these compounts determines the fruity aroma of fermented beverages. Esters represent the largest group of flavour compounds in alcoholic beverages. In beer, the major esters are ethyl acetate, isobutyl acetate, isoamyl acetate, phenylethyl acetate and the C6-C10 medium chain-fatty acid (MCFA) ethyl esters"
Isn't it gripping? And it keeps getting better. One important thing is the concentration of individual esters, rather than the total ester level. Of the esters mentioned only one of them is above the flavour threshold in most lager beers. Now that didn't come as much of a surprise, as I knew the cold fermentations of lagers produce less esters than warm ale fermentations. But who'd have thought that the ester that can be tasted in lagers in isoamyl acetate? That's right, the one that tastes of banana and is particularly known for its high levels in German wheat beer. I'm almost tempted to go an buy a lager just to see if I can notice it.  Almost, I said.

Esters ares synthesised from two substrates: an alcohol and a carboxylic acid, and a number of factors can influence this. They can be divided into: yeast characteristics, medium composition and fermentation parameters.

Selection of yeast strain is important as each yeast strain produces a specific ester profile. Though higher levels of esters are found in ales than lagers this is due to higher fermentation temperature and "there is no conclusive evidence to support the idea of higher production of esters by ale yeast, all other conditions being kept constant". Who'd have thought it?

Contradictory results have been found in studies on pitching rate and yeast performances are variable and can change through successive fermentations.

Here's a handy table about the wort composition and fermentation conditions:

Long chain unsaturated fatty acids (such as oleic acid), which mainly come from trub, decrease ester synthesis. As you'd expect from that aeration/oxygenation also decreases ester levels. Zinc stimulates yeast growth and the production of higher alcohols and their corresponding esters.

Stirring stimulates yeast growth as it increases access to nutrients and decreases carbon dioxide supersaturation. This increases higher alcohol production but decreases ester production. Increased CO2 pressure also increases higher alcohols but decreases esters.

Fermenter size and shape has a large influence on higher alcohol and ester levels. The greater liquid height in large fermenters increases dissolved CO2 with increasing hydrostatic pressure, and the shape of cyclindro-conical vessels encourages stirring. These factors decrease ester levels. Successive additions of wort during fermentation (drauflassen) can increase ester production, particularly if the added wort is not or only minimally aerated.

Increasing fermentation temperature not only increases ester levels, but changes the ester profile. Acetate esters are increased but medium chain fatty acid esters are not. Finally yeast esterases could play a significant role in the final ester profile, particularly with bottle conditioned beers (and in fact even more so if they're conditioned with Brettanomcyes but that's another story).

* The wife of one of my many bosses so I'll have to say nice things about it. But to be honest I have really enjoyed it.

Friday, 30 September 2016

The first stock pale ale in 70 years, again.

Obsessive beer nerd that I am I wouldn't normally go to the same lecture twice. But when I was invited to hear Ron Pattinson talk about stock ales in London I couldn't say no, despite having already heard him give that talk in Amsterdam. It just combined too many of my interests: history, Brettanomyces, and free beer.

I had high hopes about the last one. This event was being run by Goose Island (ABInBev), and their marketing budget easily covers providing enough free beer to make me regret it in the morning. In fact the budget clearly stretches considerable further than that, as they'd flown over a brewer from Chicago again, and Ron got to go over there himself, as well as visit London.

There's definitely something to be said for big breweries with big budgets. It's amazing to see the amount of effort that went into making this beer, and no way are they going to get their costs back from the amount of beer they have to sell.

I'm not going to go into more detail about the beer, as I did that back in July, and anyway, Bryan and Martyn have already written up the night. I will say I had a cracking time though. Long may breweries with big budgets put great efforts into re-creating historic beers, and giving me free samples!

Saturday, 24 September 2016

The past and future of hops

The latest IBD meeting I attended was about the perennial favourite hops. First we had Dr Peter Darby of Wye Hops showing us round the hop collection at Queen Court Farm. 

There are 250 varieties growing here, historic varieties and interesting breeding lines.

It's a whopper
All dwarf varieties are descended from this male
 We got to hear about hop history too, including I'm pleased to say the importance of Farnham.

Mathon may be in the midlands but this plant originated in Farnham
Then it was back to Shepherd Neame brewery to hear some more fascinating facts.

Several topics were covered in the talk.

When Wye College was closed down by the institution I studied microbiology at great efforts were made to save the hop collection.

The main site is at China Farm, and Queen Court acts as a back up.

The changing taste in hops has led to a re-evaluation of the varieties in the national hop collection.

Already Keyworths have been returned to production, and we can now add OZ97a, now known as Ernest. It's named after Ernest Salmon, the great hop breeder, as it's one of his varieties.

As every hop seedling is a new variety there has been a proliferation of new varieties in recent years, not just from hop breeders but also hop growers and hop merchants.

At Wye Hops they changed direction to start breeding for flavour in 2011, taking Cascade as their starting point. In England it crops very late so it was bred with early males to try and bring this forward. Breeding for specific oil and inbreeding to increase desired characteristics was then carried out. Cascade itself the result of a lot of Fuggle inbreeding (and Citra is a result of Hallertauer mittelfrüh inbreeding). Hop merchants Charles Faram have open pollinated Cascade  to get Jester and Olicana.

Efforts to breed a wilt-resistant Fuggle have also continued and after at least 60 years finally seems to be bearing fruit. Or should that be cones?

The English hop breeding programme has beer based on Goldings, as though they're susceptible to wilt they carry genes (presumably recessive) for wilt resistance. Fuggles have no resistance at all but it has finally reached the stage that three Fuggle seedlings have been bred with wilt resistance. 

They are now undergoing farm trials and look very promising.

Resistance to aphids has been a continuing focus, as apart from Boadicea, (which only makes up 3% of the crop) all English hops need spraying for aphids. A problem is that Boadicea and its progeny have a very distinctive smell, which many dislike. In 2014 a selection was finally made of a seedling without this characteristic. 

Advances in genetics have allowed precision breeding using marker assisted selection to start taking place.

Early genetic investigations into hops were too crude to be of use to hop breeders.

But over the years techniques have become more sensitive to the point that known genetic markers can be tied to traits seen in the phenotype.

SNP (Single Nucleotide Polymorphisms) can now be used to screen seedlings for traits as early as six weeks after sowing, greatly increasing the speed and efficiency of hop breeding.

It is not however without its problems, and is still to expensive to use for all seedlings.

A series of crosses have been made from four hops varieties to find markers for four types of characteristics: Fuggle (traditional), Cascade (new), Pilgrim (disease resistance) and Boadicea (aphid resistance)

This is being carried with a number of different institutions, and it is possible that it is from one of these places that Peter Darby's successor will come.

New challenges are still affecting the hop industry and climate change is one of them. People are now looking for drought resistance and it is now not just Bramling cross that is failing to thrive due to Winters being too mild. After this excellent talk no-one could argue with the final point that more hop research is essential!

Friday, 16 September 2016

Some clarity on finings

Once again it's clear there is still a lot of confusion about finings. Finings are used to help make beer clear by causing haze forming particles to clump together and thus drop out of suspension faster.

The confusion comes because there are different types of particles that cause different types of hazes and different types of finings are used to remove them.

  • Copper finings originate from seaweed (irish moss), have a negative charge and are added in the copper (kettle) to help remove protein.
  • Auxiliary finings can also originate from seaweed or can be silicate based. They have a negative charge and are added to the fermenter, conditioning tank or cask to help remove protein.
  • Isinglass finings originate from the swim bladders of some tropical fish. They have a positive charge and are added in the conditioning tank or cask to help remove yeast.

A large reason for the action of the finings is due to the charge they have. Opposite charges attract so negatively charge finings attract proteins (which are positively charged), and positively charged finings attract yeast (which is negatively charged). This is why finings cannot be used interchangeably and finings made from seaweed will not help remove yeast. Neither will PVPP so don't start on that. Or silica gels either. If you're after more information I recently posted at great length about hazes caused by non-microbiological particles, and part two on microbiological hazes is in the latest issue of the SIBA journal and will be posted here in due course. 

Thursday, 15 September 2016

Dealing with beer haze part one

Beer hazes can be divided into microbial (i.e. caused by bacteria or yeast) and non-microbial. There are also various types of non-microbial hazes, but the most common is that caused by protein-polyphenol complexes and I will focus on that in this article.

Protein-polyphenol complexes are a major component of trub, hot break, cold break, chill haze and some permanent hazes. They are formed when haze forming proteins bind with haze forming polyphenols (tanninogens). When these complexes form particles large enough to precipitate they cause a haze. At first these particles are less soluble at lower temperatures so reversible chill hazes can appear when beer is cooled.

Predominantly they originate from the malt but a number of factors at various stages of the brewing process can contribute to their existence. This goes to the very start of the brewing process, as the correct mineral composition of brewing liquor is important to prevent their formation. Calcium levels in brewing liquor should be greater than100mg/l and the residual alkalinity as carbonate should be less than 50mg/l. Calcium has the effect of lowering the pH of the mash, and carbonate will keep the pH high. You should aim for a mash pH of around 5.2 to 5.4. If the pH is too high more polyphenols will be extracted from the malt and the beer is more likely to be hazy. The most common way of removing carbonate is to add food grade acid to the Hot Liquor Tank, and calcium salts can be added by mixing them in with the grist. The choice of acids and salts used will affect the chloride/sulphate ratio of the beer which will have some effect on the flavour.

The protein component of hazes will come from the malt and if the total nitrogen content is over 1.65% haze is more likely to form. Protein content can be lowered by using a proportion of low protein adjuncts, such as sugar or rice, to make up some of the extract. It is also possible to get malt from barley varieties that have been bred to remove the haze forming polyphenol proanthocyanidin. The use of “ProAnt” free malt will reduce the formation of haze in beer.

Over sparging of the mash will cause more polyphenols to be extracted into the wort. The more the mash is sparged the more it will lose its buffering capacity and the pH will start to rise. To prevent high levels of tannins being extracted stop sparging when the gravity of the last runnings has dropped to 1.005.

During the boil the hot break will form as proteins coagulate, which can be removed as trub with the hops. Copper finings, a polysaccharide derived from seaweed, should be added towards the end of the boil to aid cold break formation and the subsequent removal of more protein-polyphenol complexes. The addition rate for copper finings should be optimised as over or under addition will give poor fining action. Ideally the addition rate is optimised for each batch of malt.

Polyphenols from hops will be extracted during the boil and can contribute to haze, particularly in highly hopped beers.

Protease enzymes can be added to the fermenter to break down haze forming proteins. This also has the benefit of making the beer gluten free! Auxiliary finings, polysaccharide or silicate based, can also be added to the fermenter or conditioning tank and will also help with protein removal. They can even be added to the cask, but should not be added at the same time as isinglass finings or they will bind to each other!

Other processing aids available to brewers can also help reduce haze. Silica hydrogel or xerogel will also help remove haze forming proteins, and PVPP can be used to remove haze forming polyphenols. These products are available in a mix containing both of them, which is usually added prior to filtration, though they can be used without filtration and left to settle in a tank. Rather counter intuitively tannins can also be added to beer to help clarify it. Adding an excess of polyphenols in the form of tannic acid means more protein-polyphenol complexes are formed and can be removed in the brewery.

The fact that more haze forming particles come out of suspension at lower temperatures can be used to our advantage. Cold conditioning prior to filtration, at a temperature of 0ºC or lower, will maximise the amount of haze particles removed and make a clearer and more stable beer.

This post comes from a talk I gave at the SIBA conference that I then wrote up for their magazine.

Sunday, 4 September 2016

Brettanomyces flavour

The trouble with serious writing is it's bloody hard work. I've been doing some serious writing on Brettanomyces of late and it's been a painfully slow process grinding out the words. Still, I have found some fascinating facts. 

Whilst looking into the Brettanomyces flavour wheel I came across some slides of a study into whether the flavours produced by 83 strains of Brett. were thought to have a positive or negative effect on wine. No admittedly Brett. has a worse effect on the flavour of wine than it does beer* but the study highlights a problem of brewing with Brettanomyces: a lot of the flavours it can produce don't taste very good.

* Ha!

Friday, 26 August 2016

Beer in a bad state

I'm trying to get together a list of how state controls have shaped what we drink in Britain. Of the top of my head there was:

  • Tax on malt and hops, which came with a ban on other ingredients and so killed off some beer styles. 
  • The Free Mash Tun act which deristricted ingredients but moved tax to the beer Original Gravity, the higher the gravity the higher the tax. The minimum tax was set at 1.030 so you didn't really get beers weaker than this.
  • The horrors of WWI, which aside from the mass imperialist slaughter, brought in restrictions on pub hours and beer strength.
  • The horrors of WWII, which aside from the mass imperialist slaughter, again had restrictions on beer strength and made the use of oats compulsory for several years.
  • Progresive Beer Duty, which has helped microbreweries boom, but has made some regional breweries cut production.
  • High Strength Beer Duty, which has wiped out beers from 7.5-8.5% ABV as far as I can seen. The corresponding low strenght beer duty relief for beers at 2.8% ABV has made this the strength of choice for bargain beer brands.  
  • The awful cultural vandalism that killed off Black beer by removing its tax ememption.
There are a few from other countries I might work in too, such as the German Reinheitsgebot; prohibition in the US, and their beer tax being on volume not strength; tax on mash tun size in Belgium; and the beer ban in Iceland. If there's anything I've missed please let me know.