Dr Cecilia HegartyDr Cecilia Hegarty is a lecturer in Entrepreneurship and works at the Northern Ireland Centre for Entrepreneurship (NICENT). NICENT is a partnership between the University of Ulster, Queen's University Belfast and the College of Agriculture, Food and Rural Enterprise (CAFRE). NICENT is committed to leading the development of entrepreneurship education in higher education in Northern Ireland. NICENT was established in 2000, and funded by the Office of Science and Technology (OST) and Invest Northern Ireland. It is one of 13 Science Enterprise Centres across the UK.



Range of flavoured ice creams

Ice cream and gelato manufacturers produce products with a range of favours. There are often significant variations in sweetness and hardness between flavours. This article provides an explanation of sweetness, how it is measured and how it can be controlled.

Relative sweetness and the Potere Dolcificante method are discussed and calculations are used to explain the differences. The limitations and disadvantages of using numerical values of sweetness are explained. Since sweetness and hardness are closely related the reader is also referred to the article on controlling hardness or resistance to scooping.

Cakes are classified as intermediate moisture foods and may be subject to spoilage by moulds. Water activity (aw), the water that is available, unbound or free, for chemical reactions and microbial growth is a major factor that can be utilised to limit or prevent microbial growth. Cakes generally have aw values ranging from 0.65-0.9.

Mould spoilage on cakes tend to occur on the surface and work has been done to model the water vapour pressure above cakes with temperature to derive models for the mould free shelf life (MFSL) of these products. The water vapour pressure above a food is determined by several factors including temperature, the water content of the food, the solutes present and the water activity in the food.

All foods have their own equilibrium relative humidity (ERH). This is the humidity at a given temperature at which the food will neither lose nor absorb moisture to or from the atmosphere.

If the food is held below its ERH it will lose moisture and become drier; above this value, it will absorb moisture from the atmosphere.  The gain or loss of water can have a major effect on a food and can influence shelf life significantly. The EHR is determined by exposing the food to carefully controlled atmospheres containing defined water vapour pressures generated using for example standard solutions of salts.

EHR and water activity (aw) are closely related. Water activity represents the ratio of the water vapour pressure of a food to the water vapour pressure of pure water under the same conditions.  Water activity is expressed as a fraction. If this is multiplied by 100 then ERH is obtained.  Most bacteria cannot grow below an aw of 0.86 (86 % ERH).

Cauvain and Seiler (1992) found that the logarithm of the MFSL had a linear relationship with EHR over the range 74-90% at 21° and 27°C.  The equations derived (equations 1 and 2):

Equation 1. Log10 (MFSL, days at 27°C) =6.42 - (0.065 x ERH%)

Equation 2. Log10 (MFSL, days at 21°C) =7.91 - (0.081 x ERH%)

can be used to determine the shelf life of new cake products rapidly and inexpensively. These equations are available in expensive commercial software for determining the MFSL of cakes.

Determine the mould free shelf life of cakes.

Literature Cited

Cauvain, S.P. and Seiler, D.A.L. (1992). Equilibrium relative humidity and the shelf life of cakes. FMBRA Report No. 150, CCFRA, Chipping Campden, UK.

How to cite this article

Mullan, W.M.A. (2015). [On-line]. Available from: https://www.dairyscience.info/index.php/cheese-starters/209-articles.html?start=60 . Accessed: 18 June, 2021.  

Many students have problems in understanding the mathematics describing the destruction of microorganisms by heat. Log reductions of pathogens and equivalent time-temperature treatments along with the associated lethalities account for a large part of the harder to understand topics. The quiz below is a simple test of of some of the basic concepts. Note Z value is not dealt with in this quiz. If there is sufficient interest I will provide the answers.

Heat Processing Quiz

The infection of a growing bacterial culture with phage is initiated by the adsorption of the phage to the host cell. The specificity of adsorption of lactococcal phages and the location of phage receptor substances have been studied and has been reviewed (Lawrence et. al., 1976).

Characteristics (Denomination of Protected Origin 12 June 1996) - Grana Padano is a cylindrical cheese with a diameter of 35-40 cm, an edge of 18-25 cm and a weight of 24-40 kg. Ripening lasts at least 270 days. The crust is hard, regular with a dark beige colour. The dough is white or pale-yellow with very small and sparse holes. The texture is solid, granular and the odour aromatic with almond characteristics. The taste is very savoury and mainly salty.

What are starter concentrates?

Traditionally 'bulk starter' in liquid form was used to inoculate the milk used in the manufacture of cheese, yoghurt, buttermilk and other fermented products. Over the past 15-20 years, the use of starter cell concentrates designated as either Direct Vat Set (DVS) or Direct Vat Inoculation (DVI) cultures are increasing being used, particularly in small plants, to replace bulk starter in cheese manufacture.  DVI / DVS cultures for cheese manufacture normally contain defined blends of lactococci and Streptococcus thermophilus. These organisms respond different to salt and temperature and these differences, if not understood, can impact on cheese quality.

Note that the terms DVI and DVS are used interchangeably although particular culture suppliers will tend to use only one term.

In addition to these high activity cell concentrates, lower activity commercial cell concentrates have been used for many years to inoculate milk for bulk starter manufacture, and in the manufacture of 'long set products' that require extended incubation.

Milk is an excellent source of well balanced nutrients and also exhibits a range of biological activities that influence digestion, metabolic responses to absorbed nutrients, growth and development of specific organs, and resistance to disease. These biological activities are mainly due to the peptides and proteins in milk. However, some of the biological activity of milk protein components is latent, and is released only upon proteolytic action. Bioactive peptides are produced during digestion of milk in the gastrointestinal tract, and also during fermentation and food processing.

Bioactive peptides have been defined as specific protein fragments that have a positive impact on body functions or conditions and may ultimately influence health. Upon oral administration, bioactive peptides, may affect the major body systems—namely, the cardiovascular, digestive, immune and nervous systems. The beneficial health effects may be classified as antimicrobial, antioxidative, antithrombotic, antihypertensive, antimicrobial or immunomodulatory (FitzGerald and Meisel, 2003; Korhonen and Pihlanto, 2003a).

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I have included a range of calculators e.g. aids for determining yield, milk component retention in cheese manufacture, ice-cream mix composition and the F-value of thermal processes. Wizards to help students produce correctly cited references have also been included. These aids are included for the use of students and trainees and are not intended for commercial use or to replace support from lecturers and tutors.

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The views expressed are either mine or those of the other contributors. Note contributing authors, including those posting in the forum, are solely responsible for the content of their articles including all views and statements made. 

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Dr Michael Mullan, FIFST
Dairy Science and Food Technology website


The purpose of this section is to provide some advice on how the nutrient density or energy content of foods is calculated and displayed on food labels. A calculator is also included to enable students producing new products to calculate the energy density using the chemical constituents of the food. The calculator can also be used as a food calorie calculator.

Food manufacturers in most countries are legally obliged to make several declarations on food labels. The UK Food Standards Agency has a very good overview of labelling from a consumer perspective including an interesting review of public perception of labels .


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