I'm Afraid It's Terminal

My most recent attempt at propagating a yeast starter has proved disastrous. I had hoped to produce a large cell mass and use my nerdy beer equipment to do a cell count and pitch a known number of cells per mililitre of wort, but this plan came to an abrupt end when I removed the foil from the flask to take a sample for counting and was met with the unmistakable smell of contamination. In case you don't know, this smell is identical to the phenolic fluid that the local council use to wash out lanes and such that have been used as a communal urinal by non community minded individuals. If you have been spared the unpleasant experience of passing a lane that has been washed out thusly, the classic association with this smell is hospitals in the old days when everything was scrubbed with phenol and super bugs gave them a wide birth.

I was miffed with this turn of events because I have never suffered a spoiled yeast starter before, but know exactly where the contamination crept in. My usual method of aeration is to vigorously shake the flask of wort in much the same way I strenuously shake the 25 litre carboy of wort before fermentation kicks off. This time, however, I took the advice of an American website which suggested shaking smaller volumes in a separate vessel and pouring into the primary flask. I was keen to get as much oxygen into the wort as possible, but was all too aware that this method required the wort contacting far more surfaces and atmosphere than I like. I'll be sticking to the tried and tested next time.

The pictures with this post are microscope shots of the contaminated starter. I must admit to being a little confused by it all because my experience with yeast morphology is limited. What we are looking at is either the smaller desired yeast strain along with a typically larger wild yeast strain that caused the nasty smell, or we are looking at the larger desired yeast strain accompanied with smaller bacterial cells. I'm not certain, but there's definitely something in there that shouldn't be.

Stir it up

As I mentioned in my last post I used a liquid yeast to ferment my latest brew. I had stayed away from liquid yeast for the last while because I didn't think I was getting the best from them. Coupled with this was the extra expense involved because liquid yeast strains are up to four times the cost of dried yeast sachets so I wanted to make the most of the investment. To this end I invested in some equipment which should help in the propagation of yeast from starter packs. Working in a lab brings to my attention all manner of equipment that is of great use for home brewing but might seem a little excessive to the home brewer who is not familiar with them. The simplest of this equipment is a selection of flasks that are well suited to yeast propagation, which when coupled with a magnetic stirring plate are a very effective way of persuading yeast to grow.

To see why these pieces of equipment are useful in propagating yeast we must venture into a little yeast biochemistry and metabolism for an explanation. Yeast are wonderful survival machines with the ability to survive in both aerobic and anaerobic environments. In an anaerobic environment such as brewers wort yeast use the sugars to produce energy with ethanol produced as a glorious waste product. If however yeast find themselves in an aerobic environment they respire much like us producing carbon dioxide and water. With this is mind we can see that it is very important that the environment that yeast finds itself in during beer fermentation must be anaerobic otherwise we would have the horrifying situation of no ethanol production, vast amounts of yeast cells and a strange liquid that couldn't really be described as beer. Thankfully, there is no way that brewers can accidentally aerate to such as extent that ethanol production is completely inhibited. However at the beginning of fermentation a certain degree of oxygenation is essential to set the yeast up for the work they have ahead. Before pitching, yeast is usually stored for a period during which it has to rely upon its own reserves to survive. These reserves are rapidly depleted during storage and yeast is in no position to effectively ferment beer when it is pitched. A ready supply of oxygen at the beginning of fermentation is necessary for the yeast to replenish itself and and produce sterols to make the cell wall permeable to the wort constituents. Also during this period there is an increase in the number of cells, as cell proliferation occurs at the expense of ethanol production in the aerobic environment. It is after this stage that things kick off and a vigorous fermentation ensues with lots of gas production accompanied by copious foam and ethanol, of course.

With this little bit of information in mind the objective of yeast propagation can be laid out. Liquid yeast for home brewing is in a depleted state, ready and waiting for a chance to grow. The number of cells in the average yeast pouch is insufficient to pitch, so a propagation step is needed. This step is essentially the same as the first aerobic stage of fermentation and this is where my equipment comes into use. Sterile aerated wort is placed in a flask and the depleted yeast pouch is added to the wort where it is continually mixed on the magnetic stirrer. The aim of this exercise is to produce as many yeast cells as possible to meet the pitching rate required for the gravity of the beer, which is easily done in an aerobic environment where the yeast will proliferate rather than produce ethanol. The mixing plate keeps the cells in contact with the wort ensuring maximum use of the sugar available, and also mixes the oxygen making it available to the yeast. Studies suggest that greater cell counts can be achieved with this method and it is also a hell of a lot handier than having to shake the flask every time you walk by it.

Generally a much faster start to fermentations can be had this way because the yeast is ready to go when pitched which has many advantages in the home brew environment, the main one of which is not having a big bucket of nutritious sweet wort laying about the place just screaming out for some opportunistic bug to come along and ruin. Once the fermentation kicks off the pH starts to drop rapidly creating an acidic environment that suits only the hardiest of bugs (and they sadly are quite common) and the increase production of ethanol contributes further to the inhospitable environment.

I'll leave it at that because the other great aspect to using liquid yeast is the complexity they bring to beers, which is often greater than that of dried strains. But this is a touchy subject with home brewers because some believe that dried strains are just as good. I don't agree, and that debate is worthy of its own post at a later time.

Industrial Stout

Every so often I get an urge to brew a dark beer. Usually this desire stems from a commercial beer that tickles me, and so it was with this stout. The impetus came from supping upon Black Pearl Stout brewed my Messrs. McMaguire here in Dublin. It is a proper stout with decent roasted and bitter notes and offers so much more than the nitrogentated stouts produced by the big brewers. As I said before, I don't really try to clone commercial beer, but I was certainly looking for the rich flavour that Black Pearl offered, so I upped the amount of roasted barley I usually add and threw in a measure of black malt, which may well be the undoing of this beer, and I also increased the bittering hops and made small aroma addition too. The flaked barley should give a voluminous frothy head, which is something I have always enjoyed about bottled Guinness and think every stout should have.

4.6 kg Maris Otter
600g Roasted Barley
500g Flaked Barley
250g Black Malt

Mashed at 68 C

12.5 Plato

45g 9% AA Target 60 mins
20g First Gold 20 mins

48 IBU

White Labs Irish Ale Yeast

It looked and smelled delicious during the whole process, particularly the black malt which had a distinct coffee aroma. Mashing in is one of my favourite steps during the brew because of the wholesome smell that develops when the malt hits the hot water. It smells so damn nutritious, but this mash was better then most because of the roasted grains. The boil was beautiful too with an almost cappuccino like foam forming on the top of the wort. I don't think I have come across a process that offers quite so much intrinsic worth to me. The brewing process itself is very fulfilling even without the invariably tasty end product.

I used a liquid yeast for the first time in quite a while having brewed a spell using only dried yeast. I nursed a yeast starter of Irish ale yeast all week long that I grew from an old vial from White Labs. I bought some equipment to aid me in this process which I'll post about soon, but the end result was a fabulous fermentation that started in a matter of hours and spilled from bottle I put the blow off tube into. Haven't had one of those in a while, though I did fill the carboy to the brim. The carboy is jet black with a fabulous tan head trapped inside bubbling away very satisfactorily. I'm looking forward to sampling this, and I can think of a few others who might be equally excited at the prospect.

Go forth and Flocculate

This is the first of the technical posts I warned you about. Depending on the depth of your geekery you will either stop reading very shortly indeed, or lap up the wonderful information I am about to pour forth with.

I read up on flocculation recently in order to write an assignment for my brewing course and learned a number of interesting things in the process. I knew little of the mechanism of yeast flocculation, and was interested to learn that it appears to one of those things that is of little use to the yeast themselves, but crucial to the production of the beer we all love so much. First of all, flocculation was mistakenly attributed to individual yeast cells merely falling from suspension under the action of gravity and collecting in a smelly mass at the bottom of the fermenter. Studies have shown that flocculation actually involves complex interaction between groups of cells that clump together at very specific times in the fermentation cycle. Usually this is during the stationary phase of yeast growth when they have carried out the sterling work of transforming the sugars into ethanol.

In order to understand why the yeast decide to flocculate during this phase of fermentation we must turn to the yeast cell wall and look at the manner in which the cells stick together. The current thinking in yeast studies refers to the 'lectin theory of flocculation'. Lectins are long chain like molecules that stick out from the cell and bind to receptors on neighbouring cells. The receptors are also binding points for sugars, which wort is awash with. This is why most yeast strains will not flocculate before all the sugars are gone; the receptors are tied up with sugars and the long lectin molecules cannot gain access and hook up with the neighbouring cell. From a practical point of view this might explain why that beer you want for the stag night next weekend is refusing to clear; there is just too much priming sugar floating around and the yeast hasn't managed to get through it all yet.

Further practical issues with flocculation involve either premature flocculation, or a stubborn refusal to flocculate at all. Flocculation too early in the fermentation process results in under attenuation of the beer, with resultant alteration to expected character through excess residual extract and drop in ABV. Refusal to flocculate causes over attenuation, and a hazy beer if you're a home brewer, or a massive load on the filtration system if you are a commercial brewer.

There are a number of ways to reduce possible problems with flocculation, the most obvious of which is to avoid those strains of yeast that are known to hang about longer in the beer than is perhaps useful, or drop like a stone at the first opportunity. Certain beer styles require very specific flocculation characteristics to achieve distinctive flavour and body. The strain used by Fuller's for their ESB comes to mind because it flocculates very readily, and this gives the familiar full body caused by high residual extract.

A further way to maintain expected flocculation patterns is to ensure there is sufficient calcium present in the wort. Calcium is absolutely critical for all flocculation as well as mashing and break production, so add it to the brewing liquor if it's in short supply.